ISSN NUMBER: 1938-7172
Issue 5.9 VOLUME 5 | NUMBER 9

Editor:
Michael A. Fiedler, PhD, CRNA

Contributing Editors:
Penelope S Benedik, PhD, CRNA, RRT
Mary A Golinski, PhD, CRNA
Gerard Hogan Jr., DNSc, CRNA
Alfred E Lupien, PhD, CRNA
Lisa Osborne, PhD, CRNA
Dennis Spence, PhD, CRNA
Cassy Taylor, DNP, DMP, CRNA
Steven R Wooden, DNP, CRNA

Assistant Editor
Jessica Floyd, BS

A Publication of Lifelong Learning, LLC © Copyright 2011

New health information becomes available constantly. While we strive to provide accurate information, factual and typographical errors may occur. The authors, editors, publisher, and Lifelong Learning, LLC is/are not responsible for any errors or omissions in the information presented. We endeavor to provide accurate information helpful in your clinical practice. Remember, though, that there is a lot of information out there and we are only presenting some of it here. Also, the comments of contributors represent their personal views, colored by their knowledge, understanding, experience, and judgment which may differ from yours. Their comments are written without knowing details of the clinical situation in which you may apply the information. In the end, your clinical decisions should be based upon your best judgment for each specific patient situation. We do not accept responsibility for clinical decisions or outcomes.

Table of Contents

EDITORIAL
  Obstructive Sleep Apnea and Anesthesia: What We Know and What We Donít
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GENERAL
  Respiratory and sleep effects of remifentanil in volunteers with moderate obstructive sleep apnea
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STOP questionnaire: a tool to screen patients for obstructive sleep apnea
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Association of sleep-disordered breathing with postoperative complications
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Prevalence of undiagnosed obstructive sleep apnea among adult surgical patients in an academic medical center
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A screening instrument for sleep apnea predicts airway maneuvers in patients undergoing advanced endoscopic procedures
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  Identification of patients at risk for postoperative respiratory complications using a preoperative obstructive sleep apnea screening tool and postanesthesia assessment
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  Preoperative predictors of difficult intubation in patients with obstructive sleep apnea syndrome
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  Obstructive sleep apnea is not a risk factor for difficult intubation in morbidly obese patients
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The relationship between the predictors of obstructive sleep apnea and difficult intubation
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  Postoperative complications in patients with obstructive sleep apnea syndrome undergoing hip or knee replacement: a case-control study
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Postoperative complications in patients with obstructive sleep apnea: a retrospective matched cohort study
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Perioperative pulmonary outcomes in patients with sleep apnea after noncardiac surgery
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SPECIAL ISSUE
 
This is a special Single Topic Issue of Anesthesia Abstracts. This issue is devoted to Obstructive Sleep Apnea and it's effect on clinical outcomes. It was prepared exclusively for Anesthesia Abstracts subscribers by Dennis Spence, PhD, CRNA. Dr. Spence an Adjunct Assistant Professor at the Uniformed Services University of the Health Sciences Graduate School of Nursing.

 

Does your group or institution pay for CRNA Continuing Education? Anesthesia Abstracts is available as a group subscription. Anesthesia Abstracts is AANA approved for 24 CE credits a year. A group subscription to Anesthesia Abstracts is more convenient and much less costly than traditional CE meetings. Plus, there is no expense for travel or hotel. Keep up-to-date with current anesthesia knowledge plus earn Continuing Education credit. You can earn CE anytime with Anesthesia Abstracts. Add our live CE webinars for an even greater value. Go to LifelongLearningLLC.com for more information or call us to see how much you can save at 800.586.1425.

 

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Editorial
Obstructive Sleep Apnea and Anesthesia: What We Know and What We Donít

Obstructive sleep apnea is characterized by chronic, frequent airway obstruction during sleep. These frequent obstructions result in hypercarbia and hypoxemia, which, over time, contribute to significant morbidity and mortality. Comorbidities associated with obstructive sleep apnea include such things as hypertension, coronary artery disease, congestive heart failure, atrial fibrillation, pulmonary hypertension, stroke, obesity, type II diabetes, and gastroesophageal disease. It has been estimated that 11% of men and 5% of women have moderate to severe obstructive sleep apnea. However, what is concerning to anesthesia providers is that 82% of men and 93% of women with moderate to severe obstructive sleep apnea have never been diagnosed.1 This finding has significant implications for anesthesia providers because patients with obstructive sleep apnea are at increased risk for perioperative complications. Thus, it is essential that anesthesia providers understand the pathophysiology, anesthetic implications, and potential complications associated with obstructive sleep apnea.

 
There has been quite a bit of research on obstructive sleep apnea over the last 10 years. These research findings have greatly increased our understanding of obstructive sleep apnea, however there is still a lot we do not know. Recently a new society was formed, called the Society of Anesthesia and Sleep Medicine (SASM; http://anesthesiaandsleep.org), to encourage exploration of the substantial common ground that exists between Anesthesiology and Sleep Medicine. I suspect in the near future we will see increasing multidisciplinary research from anesthesia and sleep medicine providers that builds on the existing body of knowledge in obstructive sleep apnea and anesthesia. In this issue of Anesthesia Abstracts we explore some of that research. My hope is that this issue will help you understand and think about ways you can apply these research findings to clinical practice.
 
In this issue I have chosen 12 articles on obstructive sleep apnea to review. I specifically chose these articles because their findings have implications for preoperative, intraoperative, and postoperative management of patients with obstructive sleep apnea (Table 1). As you read the abstracts you will see that a significant number of patients presenting for surgery have undiagnosed sleep apnea. You will also read investigations that demonstrate that obstructive sleep apnea, especially severe obstructive sleep apnea, is associated with an increased rate of difficult intubation. Not surprisingly, patients with obstructive sleep apnea are also more likely to experience apnea and oxygen desaturation in the recovery room after surgery.

 

 

Table 1. Obstructive Sleep Apnea Study Outcomes

 

 

P

R

E

O

P

 

S

c

r

e

e

n

 

 

A

i

r

w

a

y

I

n

t

r

a

o

p

 

E

v

e

n

t

s

 

P

A

C

U

 

E

v

e

n

t

s

C

o

m

p

l

i

c

a

t

i

o

n

s

 

 

 

 

O

p

o

i

d

s

Gupta 2001

 

 

 

 

X

 

Kim 2006

 

X

 

 

 

 

Chung 2008

X

 

 

 

 

 

Hwang 2008

X

 

 

 

X

 

Meligan 2009

 

X

 

 

 

 

Laio 2009

 

X

 

 

X

 

Finkel 2009

X

 

 

 

 

 

Cote 2010

X

 

X

 

 

 

Gali 2010

X

 

 

X

X

 

Kim 2011

 

X

 

 

 

 

Bernards 2011

 

 

 

 

 

X

Memtsoudis 2011

 

 

 

 

X

 

 

 

 

Five of the studies reviewed examined postoperative complications in patients with known or suspected obstructive sleep apnea. Every one of these studies found higher rates of postoperative complications in patients with obstructive sleep apnea. The most common complications were respiratory, especially hypoxemia. This is not surprising given that patients with obstructive sleep apnea are more sensitive to anesthetic agents and postoperative opioids, and thus are more likely to experience hypoxemia and worsening of their obstructive symptoms. However, as you read the Bernards et al. abstract, you will see that, at least in a controlled setting, remifentanil may worsen obstructive sleep apnea not by increasing obstructive events, but by increasing the frequency of central apneic episodes. Both the incidence and severity of hypoxemia was increased during sleep when patients received a remifentanil infusion.
 
Taken together, these 12 studies demonstrate that obstructive sleep apnea is a common comorbidity seen in the perioperative period, and that patients with obstructive sleep apnea may be more difficult to intubate and are at higher risk for developing postoperative respiratory complications. Unfortunately, many of the recommendations for management of patients with obstructive sleep apnea are based solely upon expert opinion, rather than on evidence from research studies. For example, if a major elective surgery patient with significant comorbidities is identified as being high risk for obstructive sleep apnea, experts recommend they should be referred to a sleep medicine physician for an overnight polysomnography.2 While this sounds right, sleep studies are expensive, and often cannot be scheduled quickly. Furthermore, there is limited evidence to show that a sleep study would change perioperative outcomes.
 
If the patient is diagnosed with moderate to severe obstructive sleep apnea then they should be started on continuous positive airway pressure (CPAP) therapy prior to surgery. If the patient with obstructive sleep apnea is currently on CPAP, it should be continued during the perioperative period. Experts also recommend that postoperative CPAP be considered in patients at high risk for obstructive sleep apnea who have recurrent PACU respiratory events. Patients with known or suspected obstructive sleep apnea who display frequent PACU respiratory events should be transferred to a unit that can closely monitor the patients with continuous pulse oximetry.2 Table 2 outlines perioperative obstructive sleep apnea precautions.
 
At a recent SASM meeting I met several investigators who reported they are currently using capnography to monitor postoperative patients at high risk for obstructive sleep apnea. At one facility all high-risk obstructive sleep apnea patients admitted to a postoperative surgical ward are placed on continuous pulse oximetry and capnography. They are also placed in rooms close to the Nurses’ station. If the patient has an apneic or hypopneic episode, or if they desaturate, the nurse is notified via a pager system.

 

 

Table 2. Perioperative Obstructive Sleep Apnea Precautions

  • Minimize preoperative sedation. Consider use of alpha-2-agonists (dexmedetomidine) to decrease anesthetic requirements.
  • Prepare for possible difficult airway.
  • Minimize use of long acting opioids. Consider using multimodal analgesic techniques and regional anesthesia when possible.
  • Use short acting inhaled or intravenous anesthetics intraoperatively (e.g. desflurane, sevoflurane, propofol ,remifentanil).
  • Use capnography during monitored anesthetic care.
  • Ensure full reversal of neuromuscular blockade. Ensure patient is fully conscious and cooperative prior to extubation.
  • Use non-supine posture for extubation and recovery. 
  • Resume or consider use of CPAP therapy.

 

 

There still are many unanswered questions with regards to obstructive sleep apnea and anesthesia. More outcomes research is needed to determine if obtaining a polysomnography examination reduces postoperative complications. Can home sleep studies be used instead of polysomnography examinations? What are the cost-benefits associated with this practice? We need evidence to support the use of CPAP postoperatively in patients at high risk for obstructive sleep apnea. If a patient needs CPAP, can they safely be managed on a postoperative surgical ward, or do they need more intensive monitoring? Can capnography be used in combination with pulse oximetry to monitor patients postoperatively? Can these monitors be used on surgical wards to “closely monitor” obstructive sleep apnea patients? These are just a few questions I think we still need answers too. In the meantime all we can do is base our practice on current evidence, expert opinion, and sound clinical decision making. I think by becoming more aware of how to identify and manage patients with obstructive sleep apnea we can reduce postoperative complications. I hope this issue of Anesthesia Abstracts will increase your awareness of the anesthetic implications of obstructive sleep apnea.

Dennis Spence, PhD, CRNA


1. Chung SA, Yuan H, Chung F. A systemic review of obstructive sleep apnea and its implications for anesthesiologists. Anesth Analg. 2008;107:1543-1563.

2. Seet E, Chung F. Management of sleep apnea in adults- functional algorithms for the perioperative period: continuing professional development. Can J Anesth. 2010;57: 849-65.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011




General
Respiratory and sleep effects of remifentanil in volunteers with moderate obstructive sleep apnea

Anesthesiology 2009;110:41-49

Bernards CM, Knowlton SL, Schmidt DF, DePaso WJ, Lee MK, McDonald SB, Bains OS


Abstract

Purpose The purpose of this study was to determine the respiratory and sleep effects of remifentanil in volunteers with moderate obstructive sleep apnea (OSA).

 

Background Obstructive sleep apnea results in partial or complete obstruction of the airway during sleep. These frequent airway obstructions can result in intermittent hypercarbia and hypoxemia, which are associated with the development of cardiovascular and cerebrovascular morbidity. It has been estimated that 9% of women and 27% of men between 30 and 60 years old have OSA.

 

Obstructive sleep apnea patients experience frequent apneic and hypopneic episodes during sleep. During rapid eye movement sleep (REM), pharyngeal muscle tone is generally the lowest and as a result airway obstructions are more common during this period of sleep. The apneic and hypopneic events that occur during sleep are relieved when the patient arouses secondary to an increased respiratory drive in response to hypercarbia and/or hypoxemia. However, opioids, which are frequently used during anesthesia, blunt the ventilatory response to hypercarbia and hypoxemia. This is why patients with OSA are more sensitive to opioids and may be vulnerable to significant respiratory morbidity and mortality. As a result, practice guidelines have been published for anesthesia providers recommending caution when administering opioids to patients with OSA because it is assumed that opioids will worsen the OSA symptoms during sleep. Unfortunately, these recommendations have been based largely on expert opinion and not on prospective studies which have evaluated the respiratory and sleep effects of opioids on patients with OSA.

 

The investigators of this study hypothesized that opioids would increase the number and severity of apneic and hypopneic episodes during natural sleep in patients with OSA.

 

Methodology This was a prospective, randomized, double-blind, placebo controlled investigation of opioid pharmacology in patients with moderate OSA. A total of 19 patients with moderate OSA were enrolled. Moderate OSA patients had an apnea hypopnea index (AHI) from 15-30. Patients with chronic lung disease, coronary artery disease, breast feeding or pregnancy, chronic opioid or sedative use, or continuous positive pressure use during sleep within 7 days of the study were excluded. Patients were also excluded if they had recently gained or lost > 10 lbs. All patients completed a polysomnography examination before enrollment as part of their OSA workup. Results of this study were compared to this baseline examination. Patients were randomly assigned to receive either a remifentanil infusion at 0.075 mcg/kg/min or a saline infusion during an overnight polysomnography examination. The remifentanil dose was based on lean body mass. Patients and sleep technologists scoring the polysomnography were blinded to the study group.

 

Data collected included baseline demographics, sleep stages, apneas, hypopneas, and oxygen saturations. Polysomnography results were compared with the patients’ baseline polysomnography examination. Blood was drawn in the morning after the sleep study to measure remifentanil plasma concentrations. Statistical analyses were appropriate. A P < 0.05 was significant.

 

Result No significant differences were found in baseline demographics or in time between the two sleep studies between the two groups. There were 9 patients in the saline group and 10 in the remifentanil group; 5 of 9 in the saline group were male and 6 of 10 in the remifentanil group were male.  The average age of the patients was 49.5 ± 11.5, and the approximate BMI was 33.5 kg/m2. No significant differences were found in remifentanil plasma concentrations between the two groups. Remifentanil plasma concentrations averaged 3.4 ± 0.9 ng/mL.

 

No significant differences were found between baseline and study polysomnography examination results in the saline group. In the remifentanil group, however, total sleep time and sleep efficiency was significantly lower when compared to the baseline sleep study (P < 0.05). Total sleep time decreased by 68 ± 65 min and sleep efficiency was 11% ± 14% lower. Sleep latency to stage 2, or the amount of time needed to get to stage 2 sleep, was 12.5 min longer (range: 6-113) during the remifentanil infusion as compared to the baseline study (P < 0.05). Likewise, the remifentanil infusion was associated with an increase in the amount of time in stage 1 sleep, and a decrease in the amount of REM sleep and total number of sleep stage changes compared to the baseline study (P < 0.05). Only 20% of subjects in the remifentanil group had REM sleep (P < 0.05).

 

The remifentanil infusion was also associated with a significant increase in the total number of arousals. In the remifentanil group the total number of arousals increased by a mean of 257 ± 218 (95% CI: 68-372; P < 0.05). Also, the average number of arousals per hour increased by 43 ± 30 (95% CI: 21-64; P < 0.05). This indicated that patients receiving remifentanil had an increased number of attempts to breathe during airway obstruction or movement during sleep.

 

The Apnea Hypopnea Index increased during the remifentanil infusion compared to the baseline sleep study; however this was not statistically significant (44 ± 29 vs. 24 ± 5). The number of central apneas increased significantly in the remifentanil group (17 ± 29 vs. 0.4 ± 1, P < 0.05) while the total number of obstructive apneas decreased significantly (8 ± 5 vs. 4 ± 6, P < 0.05). The total number of hypopneas increased by 7 ± 16 events per hour during the remifentanil infusion (22 ± 16 vs. 15 ± 6, P = NS). The severity, or maximum duration, of apneic or hypopneic events did not change significantly with the remifentanil infusion.

 

The overall increase in the number of central apneas resulted from large increases in only 4 patients. In these patients the number of central apneic episodes per hour increased from 0.8 at baseline to 43 during the remifentanil infusion. The central apneas did not occur during REM sleep in any of these 4 patients. Patients with central apnea were older (age, 56 ± 11 vs. 46 ± 11 y), and less obese (BMI, 28 ± 7 vs. 33 ± 8).

 

Remifentanil was associated with significant decreases in oxygen saturation while awake, during sleep, and during an apneic or hypopneic event. The lowest oxygen saturation during sleep was 87% ± 4% at baseline and 80% ± 5% during remifentanil infusion (P < 0.05). The number of desaturations per hour increased during the remifentanil infusion (6 control vs. 15 remifentanil, P = NS). The desaturations were significantly worse during the remifentanil infusion. The amount of time with oxygen saturation between 81%-90% was significantly higher during the remifentanil infusion (P < 0.05; Figure 1). During the remifentanil infusion, 18% of total sleep time was spent with oxygen saturation between 81%-90% compared to 1.4% during the baseline sleep study.

 

 

Figure 1. Comparison of Oxygen Saturations

Figure 1

 

Conclusion Obstructive Sleep Apnea was worse during remifentanil infusion because of a marked increase in the number of central sleep apneas. Obstructive events occurred less frequently overall because of decreased REM sleep. Hypoxemia was both more common and more severe during the remifentanil infusion. These results suggest that anesthesia providers should be cautious when administering opioids to patients with even moderate OSA. However, the primary risk from opioid administration may be due to central sleep apnea rather than obstructive sleep apnea.

 

Comment

Previous studies have suggested that patients with OSA are at increased risk of worsening their obstructive symptoms and more prone to hypoxemia during sleep after surgery, especially when opioids are administered for postoperative analgesia. In this laboratory study, the authors hypothesized that obstructive symptoms, as measured by the Apnea Hypopnea Index, would increase during a continuous remifentanil infusion. The investigators found just the opposite. Obstructive apneic events decreased although central apneic events increased. The investigators attributed this difference to decreased time spent in REM sleep. REM sleep is when the pharyngeal muscles are more prone to collapse resulting in obstructive symptoms. Since the amount of time spent in REM sleep was shorter, it is not surprising that the number of apneas secondary to obstruction were decreased.

 

Additionally, there were increased numbers of arousals during sleep during the remifentanil infusion. These were most likely triggered by more frequent hypercarbia and/or hypoxemia events secondary to the remifentanil infusion. This resulted in more frequent attempts to breathe or move during sleep, which helped relieve the obstructive events, and thus explains why there were decreased obstructive episodes.

 

It is important to point out that central apnea only occurred in 4 of the 10 subjects. The authors found that these patients were older and had a lower BMI. It may be that certain patients (i.e, those that are older and less obese) with OSA are prone to central apnea when administered opioids. The problem is, how do we identify those patients at risk for central apnea? Since obesity is one of the risk factors for OSA, and patients in this study with central apnea had lower BMI, is it possible that we might not identify a patient at risk for respiratory morbidity secondary to increased central apnea after administration of opioids? The authors point out that while continuous positive airway pressure (CPAP) is commonly used postoperatively in OSA patients, it will not prevent central apneic episodes. I think the take home message from this finding is that anesthesia providers should be cautious in administering opioids, especially long-acting opioids, to older patients with OSA.

 

In this study, during the remifentanil infusion oxygen saturations were lower and there was an increase in the total sleep time when oxygen saturations were between 81%-90%. This indicated that patients were experiencing more frequent episodes of moderate hypoxemia during sleep as a result of the remifentanil infusion. I believe this finding supports the theory that patients with OSA are more sensitive to opioids and prone to oxygen desaturation after administration of opioids. This finding is supported by clinical research studies which indicate that the most common postoperative complication in OSA patients is frequent hypoxemia.1 More recent research suggests OSA is an independent risk factor for serious postoperative pulmonary complications, such as aspiration, adult respiratory distress syndrome, and postoperative intubation.2

 

One important point the authors of this study brought up was that decreased obstructive episodes secondary to opioid-induced REM suppression might only be temporary. Typically, 48 to 72 hours after anesthesia or opioid administration there is a rebound in REM sleep, which may result in worsening obstructive episodes.3 It is unclear if this equates to increased risk of complication. But what it does suggest is that patients with OSA may still be at risk for worsening of their OSA symptoms after discharge home from a monitored setting.

Dennis Spence, PhD, CRNA


1. Gali B, Whalen FX, Schroeder DR, Gay PC, Plevak DJ. Identification of patients at risk for postoperative respiratory complications using a preoperative obstructive sleep apnea screening tool and postanesthesia assessment. Anesthesiology 2009;110:869-876.

2. Memtsoudis S, Liu SS, Ma Y, Chiu YL, Walz JM, Gaber-Baylis LK, Mazumdar M. Perioperative pulmonary outcomes in patients with sleep apnea after noncardiac surgery. Anesth Analg 2011;112:113-121.

3. Liao P, Sun F, Amirshahi B, Islam S, Vairavanathan S, Shapiro C, Chung F. A significant exacerbation of sleep breathing is OSA patients undergoing surgery with general anesthesia. Sleep 2009;32: A223.


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





STOP questionnaire: a tool to screen patients for obstructive sleep apnea

Anesthesiology 2008;108:812-821

Chung F, Yegneswaran B, Liao P, Chung SA, Vairavanathan S, Islam S, Khajedehi A, Shapiro CM


Abstract

Purpose The purpose of this study was to develop and validate a simple questionnaire for obstructive sleep apnea (OSA) to be used in surgical patients.

 

Background Obstructive sleep apnea affects between 2% and 26% of the general population. It is estimated that 80% to 93% of patients with moderate to severe obstructive sleep apnea are undiagnosed. Further confounding the problem is the fact that it is difficult for many patients to obtain a formal sleep study to diagnose obstructive sleep apnea. It is critical that patients with obstructive sleep apnea be identified early to minimize perioperative complications.

 

The Berlin questionnaire is one of the most widely used screening tools for obstructive sleep apnea; however, it has not been validated in surgical patients. The ASA has developed a screening tool for obstructive sleep apnea; however it too has not been validated. Furthermore, both of these questionnaires have numerous questions and confusing scoring systems, making them difficult to implement in a busy preoperative screening clinic.

 

Methodology This was an instrument development and validation study of the STOP-BANG questionnaire. The questionnaire consists of 4 questions and 4 clinical characteristics:

  • Snoring
  • Tiredness
  • Observed apnea
  • high blood Pressure
  • BMI >35 kg/m2
  • Age >50
  • Neck circumference >40 cm
  • male Gender

The questionnaire is a self-report, forced choice (yes/no) questionnaire that can be completed in less than 1 minute. It was based on the Berlin Questionnaire, consensus of a group of anesthesiologists, sleep specialists, and literature review.

 

The instrument was given to 592 surgical patients in a pilot study. All patients were invited to complete an overnight polysomnography study. Reliability of the instrument was checked with a subset of 55 patients who completed the questionnaire on two different occasions. After the pilot study 1,875 patients completed the STOP-BANG questionnaire and were invited to undergo an overnight polysomnography study to diagnose obstructive sleep apnea. A clinical diagnosis of obstructive sleep apnea was determined by the apnea hypopnea index (AHI): AHI 5-15 mild, AHI 16-30 moderate, and AHI >30 severe obstructive sleep apnea. Statistical and power analyses were appropriate. A P value < 0.05 was significant.

 

Result A total of 2,721 patients completed all items on the questionnaire. Of the 177 who completed the sleep study, 68.9% (n = 122) had an AHI > 5, indicating they had OSA. Of those who completed the sleep study, 29.4% had mild, 17.5% had moderate, and 22% had severe obstructive sleep apnea. Patients with an AHI >5 were almost 10 years older, had a higher ASA status, higher blood pressure, greater BMI, and larger neck circumference when compared to those with an AHI <5 (P < 0.05). Reliability testing of the instrument indicated that 96.4% of patients who completed the instrument a second time had the same responses (reliability coefficient: 0.923, 95% CI: 0.82-1.0).

 

Sensitivity of the 8 items on the STOP-BANG questionnaire was high. With an AHI >15 the STOP-BANG had high sensitivity and negative predictive value. Both were more than 90% for patients with moderate to severe OSA. This suggests that if a patient is classified as low risk on the STOP-BANG (score <3), then one can be highly confident they do not have moderate to severe obstructive sleep apnea. Table 1 presents the predictive parameters of the STOP-BANG.

 

 

 

Table 1. Predictive Parameters of STOP-BANG (n = 177)

AHI > 5

Sensitivity

Specificity

Positive Predictive Value

Negative Predictive Value

Odds ratio

 

83.6% (75.8-89.7)

56.4% (42.3-69.7)

81% (73-87.4)

60.8 (45.1-74.2)

1.91 (1.42-2.66)

AHI > 15

Sensitivity

Specificity

Positive Predictive Value

Negative Predictive Value

Odds ratio

 

92.9% (84.1-97.6)

43% (33.5-52.9)

51.6% (42.5-60.6)

90.2% (78.6-96.7)

9.80 (3.65-26.3)

AHI > 30

Sensitivity

Specificity

Positive Predictive Value

Negative Predictive Value

Odds ratio

 

100% (91-100)

37% (28.9-45.6)

31% (23-29.8)

100 (93-100)

>999.99

Note. Data presented as average (95% confidence interval).

 

 

Conclusion The STOP-BANG questionnaire is a reliable, valid, concise, easy to use instrument that can identify patients preoperatively who are at high risk for obstructive sleep apnea. The instrument has high sensitivity in detecting patients with moderate to severe obstructive sleep apnea.

 

Comment

This was the seminal article which demonstrated the reliability and validity of the STOP-BANG questionnaire. Numerous studies since have demonstrated the STOP-BANG questionnaire is useful in screening for obstructive sleep apnea, and predicting complications after surgery and sedation procedures.1,2,3 I have used it and have worked at several facilities were the instrument has been incorporated into the perioperative screening process. It is simple, easy to use, and easy to remember. This is especially advantageous in a busy clinical practice.

 

The STOP-BANG has high sensitivity in detecting those patients with moderate to severe obstructive sleep apnea. However, it only has moderate to low specificity, meaning it may classify some patients as having obstructive sleep apnea, who in fact do not have it. Clinically I do not think this is a significant issue, because it is better to err on the side of caution and to assume a patient might have obstructive sleep apnea and plan the perioperative management to minimize risks and complications.

 

I encourage anesthesia providers to consider incorporating the STOP-BANG questionnaire into clinical practice. It is especially important to teach other providers, nurses, and technicians about the significance of obstructive sleep apnea and how to screen patients. Implementation of the STOP-BANG would make an excellent DNP or QA project.

Dennis Spence, PhD, CRNA


1. Vasu TS, Dogharmji K, Cavallazzi R et al. Obstructive sleep apnea syndrome and postoperative complications: clinical use of the STOP-BANG questionnaire. Arch Otolaryngol Head Neck Surg 2010;136: 1020-1024.

2. Coté GA, Hovis CE, Waldbaum L et al. A screening instrument for sleep apnea predicts airway maneuvers in patients undergoing advanced endoscopic procedures. Clin Gastroenterol Hepatol 2010;8:660-665.

3. Chung F, Yegnesaran B, Liao P et al. Validation of the Berlin Quesionnaire and American Society of Anesthesiologists Checklist as screening tools for obstructive sleep apnea in surgical patients. Anesthesiology 2008;108:822-830.


Apnea was defined as cessation of breathing >10 seconds; hypopnea was a 50% reduction in breathing effort with at least a 4% decrease in SaO2. The AHI is the total number of apneic or hypopneic events per hour.

 

Sensitivity measures the percentage of patients who truly have obstructive sleep apnea who are correctly identified as having obstructive sleep apnea with the instrument. A test with a high sensitivity has a low false negative rate.

 

Specificity measures the percentage of patients who do not have obstructive sleep apnea who are correctly identified as not having obstructive sleep apnea. A test with high specificity has a low false positive rate.

 

Negative Predictive Value is the proportion of patients with a negative test who truly do not have the condition. For example if a patients scores < 3 on the STOP-BANG then it is highly unlikely they have OSA. Negative Predictive Value is closely linked to sensitivity.

 

Positive Predictive Value or precision rate is the proportion of patients with a positive test result (i.e, > 3 risk factors on STOP-BANG) who are correctly diagnosed. Positive Predictive Value is closely linked to specificity.

 

The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





Association of sleep-disordered breathing with postoperative complications

Chest 2008;133:1128-1134

Hwang D, Shakir N, Limann B, Sison C, Kalra S, Shulman L, Souza ADC, Greenberg H


Abstract

Purpose The purpose of this study was to determine if a preoperative screening protocol for obstructive sleep apnea, followed by home sleep oximetry, could identify patients who were at risk for postoperative complications.

 

Background Obstructive sleep apnea (OSA) is a form of sleep-disordered breathing which increases the risk of postoperative complications. Polysomnography is the gold standard for the diagnosis and determination of the severity of obstructive sleep apnea. Unfortunately, many patients with sleep apnea do not know they have the disorder, and for those who have symptoms consistent with obstructive sleep apnea, it is difficult to obtain a polysomnography examination prior to surgery. Published guidelines for the screening and management of patients with known or suspected obstructive sleep apnea are largely based on expert opinion. Therefore, further research is needed to determine the best strategies for screening patients with suspected obstructive sleep apnea.

 

Methodology The investigators conducted a retrospective cohort study. Medical records of adult patients who were screened for obstructive sleep apnea during their preoperative evaluation were reviewed. If patients had at least two clinical features of obstructive sleep apnea on a standardized questionnaire and physical examination, they were selected for a home nocturnal oximetry study prior to surgery. Only patients without a prior diagnosis were screened for obstructive sleep apnea. Results were made available to the anesthesia and surgical teams. If a patient had an abnormal nocturnal oximetry test result, or if the patient had a known diagnosis of obstructive sleep apnea, they underwent prolonged monitoring in the PACU.

 

Nocturnal oximetry data included the oxygen desaturation index (ODI), which was the number of episodes per hour of oxygen desaturation of ≥ 4%. Mild ODI severity was defined as 5-20, moderate as 20 to 40, and severe > 40 events per hour. Medical records were reviewed for postoperative complications. A complication was defined as an adverse event affecting a major organ system that required further monitoring, additional diagnostic testing, or direct therapeutic intervention. Hypoxemia was one of the complications, and it was defined as a decrease in oxygen saturation that required an addition or increase in supplemental oxygen. Atelectasis was determined by chest x-ray.

 

Patients with an oxygen desaturation index ≥ 5 were compared to those with an ODI <5 for the incidence of postoperative complications. Logistic regression was used to determine which risk factors were associated with postoperative complications. Because of multiple comparisons, a P < 0.03 was considered significant.

 

Result A total of 172 patients completed home oximetry testing. Their average age was 55 years (range 27 to 85 years old). Home oximetry results indicated that 57% of the patients screened had an oxygen desaturation index ≥ 5, and 43% had an ODI < 5. Overall, 34% of patients in the study had an ODI in the mild range, 17% in the moderate range, and 6% in the severe range. Patients with mild and moderate ODI results were combined. Patients with an ODI ≥ 5 were predominantly male (56% vs. 41%), with a BMI ≥ 27 kg/m2 (88% vs. 73%), and had higher rates of hypertension (62% vs. 46%) and diabetes (20% vs. 12%). The most common surgical procedure was abdominal surgery, followed by urological, gynecological, and neurosurgical. PACU length of stay was significantly longer in the ODI ≥ 5 group (11 vs. 6 hours, P = 0.004).

 

A total of 17 out of 172 patients experienced a postoperative complication (10%). All but two of the complications occurred in the oxygen desaturation index ≥ 5 group (15% vs. 3%, P = 0.008). The most common complication in the ODI ≥ 5 group was respiratory, with most patients experiencing hypoxemia and/or atelectasis (Figure 1). Treatment typically consisted of increased oxygen requirement and/or CPAP or BiPAP.

 

 

Figure 1: Complications by Oxygen Desaturation Index

Figure 1

Note: *ODI = Oxygen Desaturation Index

 

 

Logistic regression results which controlled for gender and BMI > 27 kg/m2 indicated that patients with an ODI ≥ 5 were 7.2 times more likely to experience a postoperative complication (95% CI, 1.5 to 33.3, P = 0.012).

 

Conclusion In patients with suspected obstructive sleep apnea, home oximetry testing prior to surgery predicted those patients at risk for postoperative complications. An ODI ≥ 5 was an independent predictor of postoperative complications.

 

Comment

This is another study which demonstrates that using a standardized preoperative screening process can help identify patients at risk for postoperative complications. The novel part of this study was the use of home oximetry in patients at risk for obstructive sleep apnea prior to surgery. This helped determine the severity of the sleep-disordered breathing in these patients. This is one of the few studies which reported on an obstructive sleep apnea screening protocol which used a questionnaire combined with home oximetry testing. I believe this type of protocol would be useful because it identifies patients with possible obstructive sleep apnea, determines the severity, and has a mechanism for communicating this information to the anesthesia and surgical team.

 

There are several limitations to this study. First, this was a retrospective study, so there is a risk that the results may be inaccurate due to coding errors. There is a risk of selection bias because we do not know how many patients who were offered home oximetry testing refused or did not complete the testing. It is possible that patients who completed home oximetry testing may have been at higher risk for obstructive sleep apnea. This is supported by the results, which indicate that 57% of the patients who completed the oximetry testing had an oxygen desaturation index ≥ 5, which indicates they may have obstructive sleep apnea. Additionally, the investigators did not report the total number of patients screened, which makes it difficult to determine the prevalence of possible obstructive sleep apnea at this facility. The investigators reported they used a standardized questionnaire; however, they did not state the name of the questionnaire or its reliability and validity. Though given the questions they asked I suspect it was a valid tool. Additionally, the investigators chose to categorize BMI as ≥ or < 27. I would have liked to have seen the results presented based on a BMI ≥ or < 35, since obesity is a risk factor for obstructive sleep apnea.1

 

Furthermore, the investigators chose to include all postoperative complications. Some of the reported complications were most likely related to the type of surgery. For example, two patients in the oxygen desaturation index ≥ 5 group experienced postoperative bleeding, one experienced a pulmonary embolism, and another had hypotension and junctional escape rhythm after mitral valve replacement. Some of these complications were probably related to the surgical procedure performed, as well as patient comorbidity. It would have been more appropriate if the investigators had included type of surgery as a predictor in their logistic regression model because this would have controlled for this issue. Unfortunately, their sample size was too small to include this as a predictor.

 

Despite these limitations, I think these results further demonstrate that patients with possible obstructive sleep apnea are at increased risk of respiratory complications such as hypoxemia. This study also demonstrates a good protocol for screening patients for obstructive sleep apnea. I would probably use the STOP-BANG tool in combination with home oximetry testing if I was to implement this protocol at my facility.

Dennis Spence, PhD, CRNA


1. Chung et al. STOP questionnaire: a tool to screen patients for obstructive sleep apnea. Anesthesiology 2008; 108:812-821.


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





Prevalence of undiagnosed obstructive sleep apnea among adult surgical patients in an academic medical center

Sleep Medicine 2009;10:753-58

Finkel KJ, Searleman AC, Tymkew H, Tanaka CY, Saager L, Safer-Zadeh E, Bottros M, Selvidge JA, Jacobsohn E, Pulley D, Duntley S, Becker C, Avidan MS


Abstract

Purpose The purpose of this study was to describe the prevalence of undiagnosed obstructive sleep apnea (OSA) in adult surgical patients at a single medical center using a preoperative obstructive sleep apnea screening program.

 

Background Obstructive sleep apnea is described by chronic, frequent episodes of upper airway obstruction during sleep, which results in hypoxia and hypercarbia. It is associated with increased risk of cardiovascular, neuropsychological, and endocrine disorders, and an impaired quality of life. In the United States up to 25% of adults are thought to be high risk for obstructive sleep apnea. Risk factors include obesity, male gender, smoking, and age > 40. It is estimated that 90% of people with obstructive sleep apnea are undiagnosed. Obstructive sleep apnea is associated with an increased incidence of hypertension, diabetes, atrial fibrillation, stroke, coronary artery disease, and heart failure. Patients with obstructive sleep apnea are at high risk for perioperative complications because they have increased sensitivity to opioids and anesthetic agents. Thus it is essential that anesthesia providers be aware of patients who present with actual or suspected obstructive sleep apnea.

 

The American Society of Anesthesiologists has published guidelines for the management of patients with obstructive sleep apnea. The guidelines stress the importance of screening patients for obstructive sleep apnea, and recommend modifying the anesthetic plan to minimize risks. The purpose of this single-institution observational study was to describe the prevalence of obstructive sleep apnea in adult patients presenting for surgery using a preoperative screening program.

 

Methodology This was an observational study of 2,778 adult patients (> 18 years old) presenting for elective surgery. All participants completed an obstructive sleep apnea screening questionnaire as part of the preoperative assessment. The questionnaire combined features of the Berlin questionnaire, Flemons’ index, and Epworth sleepiness scale; all validated instruments. The questionnaire had a sensitivity of 0.94 and specificity of 0.79 for predicting those at high risk for obstructive sleep apnea. The program assigned a risk level of no, low, moderate or high-risk for obstructive sleep apnea. Participants who were high-risk for obstructive sleep apnea were compared to those who were not at high-risk; those with no, low, or moderate risk.

 

Patients who were high-risk for obstructive sleep apnea were asked to complete a home sleep study using an ARES Unicorder, a validated tool for home testing of obstructive sleep apnea. The Apnea-Hypopnea Index (AHI) score was downloaded from the device on the day of surgery. The AHI represents the number of apneas and hypopneas in one hour, and is used to diagnose the severity of obstructive sleep apnea. Apnea is a complete cessation of airflow for at least 10 s, and hypopnea was defined as at least a 50% reduction in air flow, 3% decrease in saturation, and confirmatory arousal detection. The ASA stratifies obstructive sleep apnea severity according to the Apnea-Hypopnea Index (AHI) as follows:

  • 5 or less normal
  • 6-20 as mild
  • 21-40 as moderate obstructive sleep apnea
  • > 40 as severe obstructive sleep apnea

If the patient was identified as high-risk for obstructive sleep apnea based on the questionnaire they were given a wrist band, and a note was placed over the patients’ bed and in their chart, and on the operating room schedule noting this risk. Statistical analysis was appropriate. A P value < 0.05 was considered significant.

 

Result A total of 2,778 patients had complete data. Of these patients, 661 were identified as high-risk for obstructive sleep apnea (23.7%). Of these, 80% had never been diagnosed as having obstructive sleep apnea. When the patients identified as high-risk for obstructive sleep apnea who were not previously diagnosed were combined with those previously diagnosed with obstructive sleep apnea the estimated prevalence of obstructive sleep apnea was 22% (95% CI: 20.2-23.8%).

 

Patients who were high risk for obstructive sleep apnea had a significantly higher median BMI (37 vs. 27, P < 0.001), neck circumference (43 in vs. 38 in, P < 0.001), and were more likely to be African American (26.5% vs. 20%, P < 0.001). Patients who were high-risk for obstructive sleep apnea had a significantly higher incidence of hypertension (58% vs. 40%, P < 0.001) and diabetes (24.5% vs. 10.5%, P < 0.001).

 

A total of 373 were asked to complete a home sleep study, and 207 had valid study results. Of these patients, 82% were considered to have obstructive sleep apnea (Figure 1). A majority of patients had mild obstructive sleep apnea (47%; AHI 6-20). In 19 of 26 patients (73%) formal sleep studies confirmed the diagnosis of obstructive sleep apnea.

 

 

Figure 1. Home Sleep Study Results in High-Risk Patients 

Figure 1

Note. Mild OSA AHI: 6-20, moderate OSA AHI: 21-40, and severe OSA: AHI >40. OSA.

 

 

Conclusion This study demonstrated the feasibility of screening all patients presenting for preoperative evaluation for elective surgery. At this institution almost a quarter of patients presenting for elective surgery may have been at high-risk for obstructive sleep apnea.

 

Comment

This is an important study for many reasons. The most important one is that it demonstrates how a large academic medical institution was able to develop a process for identifying and communicating to all providers that a patient may be at high-risk for obstructive sleep apnea. This is important because patients with obstructive sleep apnea, especially those with severe obstructive sleep apnea, are at high risk for perioperative complications. I think we have all heard stories of patients with known or unknown obstructive sleep apnea receiving sedatives or opioids postoperatively who suffered a cardiac arrest. Having a way to identify those diagnosed with or undiagnosed but at high-risk for obstructive sleep apnea is essential to minimize risks of perioperative morbidity and mortality.

 

The investigators estimated the prevalence of obstructive sleep apnea at their institution to be 24%, with 82% of patients being undiagnosed. These results are consistent with the national prevalence of undiagnosed obstructive sleep apnea in the general population. These results provide further support for the widespread problem of obstructive sleep apnea.

 

A final important point I found in this study was that at this facility the anesthesia providers ensured that the patients and their primary care provider were notified that they were screened as being at high risk for obstructive sleep apnea. It is important that we communicate findings during the perioperative period so that patients can get adequate follow-up care or further testing, such as a formal sleep study.

Dennis Spence, PhD, CRNA


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





A screening instrument for sleep apnea predicts airway maneuvers in patients undergoing advanced endoscopic procedures

Clin Gastroenterol Hepatol 2010;8:660-665

Cotť GA, Hovis CE, Waldbaum L, Early DS, Edmundowicz SA, Azar RR, Mullady DK, Jonnalagadda SS


Abstract

Purpose The purpose of this study was to determine if a bedside screening tool for sleep apnea, called the STOP-BANG, would help identify patients requiring airway maneuvers and those at high risk for sedation-related complications.

 

Background It is estimated that over 20% of the United States population has some form of sleep-disordered breathing. Up to 93% of females and 82% of males with obstructive sleep apnea (OSA) have never been diagnosed. Patients with obstructive sleep apnea may be at increased risk for sedation-related complications during advanced endoscopy procedures because of their sensitivity to sedatives and opioids (i.e., endoscopic ultrasound [EUS], endoscopic retrograde cholangiopancreatography [ERCP]). Therefore, it is essential that patients at high risk for obstructive sleep apnea be identified.

 

The STOP-BANG is a simple screening tool that can identify patients at high risk for obstructive sleep apnea. It has been validated in perioperative patient populations, and has > 90% sensitivity to detect patients at moderate to high risk for obstructive sleep apnea. However, further research is needed to determine if the STOP-BANG is useful in identifying patients presenting for advanced endoscopy who are high risk for obstructive sleep apnea. This tool may also help identify those who may require airway maneuvers or be at risk for sedation-related complications.

 

Methodology This was a study of 231 patients scheduled for ERCP or EUS at a large academic referral center. Patients were provided with propofol-based sedation by experienced CRNAs. Sedation was provided with propofol alone or in combination with low-dose opioids and/or midazolam. All patients completed the STOP-BANG questionnaire. The questionnaire contains 4 questions and 4 clinical characteristics of obstructive sleep apnea:

  • Snoring
  • Tiredness
  • Observed apnea
  • high blood Pressure
  • BMI >35 kg/m2
  • Age >50
  • Neck circumference >40 cm
  • male Gender

A score of 3 or more indicates the patient is high risk for obstructive sleep apnea. Patients were dichotomized into high risk or low risk for obstructive sleep apnea groups. Results of the questionnaire were not provided to the CRNAs or endoscopist.

 

All patients received oxygen through a nasal cannula at 3 LPM, and had standard monitors and capnography used during the procedure. Depth of sedation was evaluated at the time of scope insertion and during the procedure with the Modified Observer’s Assessment of Alertness/Sedation (MOAA/S). ERCP procedures were performed either in the prone or lateral position. Airway maneuvers were defined as need for a chin lift, nasopharyngeal airway, modified mask airway, positive pressure ventilation, or endotracheal intubation. Sedation-related complications were defined as hypoxemia (SaO2 < 90%), hypotension (systolic blood pressure < 90 mm Hg or 25% decrease from baseline), or hypopnea/apnea (< 6 breaths/minute). Other sedation-related complications included early procedure termination for refractory laryngospasm or other events.

 

The primary outcomes of this study were to determine the frequency of high risk patients presenting for advanced endoscopy, and to compare the rates of airway maneuvers and sedation-related complications between high risk and low risk patients. Statistical and power analyses were appropriate. Relative risk scores were adjusted for ASA class 3 or higher.

 

Result Out of 231 patients, 43% were high risk and 57% were low risk for obstructive sleep apnea. Patients who were high risk were older, more likely male, obese, and had a higher Mallampati score and ASA classification. The median STOP-BANG scores in the high risk and low risk groups were 4 and 1 respectively. (> 3 is high risk for obstructive sleep apnea.) There was no significant difference in endoscopy time between the two groups. A significantly lower proportion of patients who were high risk had their procedure performed in the prone position (57% vs. 70%, P = 0.04). Mean MOAA/S scores were significantly higher in the high risk group at the time of endoscop insertion, indicating they were less deeply sedated when compared to the low risk group (P = 0.02).

 

The overall incidence of any airway maneuver was 20% in the high risk group and 6% in the low risk group. The adjusted relative risk of need for an airway maneuver was 1.7 times greater in the high risk group (95% CI: 1.28-2.24, P < 0.05; Figure 1). High risk patients were 1.63 times more likely to experience hypoxemia when compared to the low risk group (95% CI: 1.19-2.25, P < 0.05). Two patients in the high risk group experienced apnea compared to none in the low risk group. There was no significant difference in the incidence of hypotension or need to terminate the procedure early between the two groups.

 

 

Figure 1. Incidence of need for airway maneuvers

Figure 1

Note. SB+ = high risk for obstructive sleep apnea; SB- = low risk for obstructive sleep apnea.

 

 

Conclusion A large proportion of patients who presented for advanced endoscopy procedures were at high risk for obstructive sleep apnea. These patients may require more airway maneuvers and experience an increased frequency of hypoxemia.

 

Comment

Identifying patients at high risk for obstructive sleep apnea is critical to minimizing morbidity and mortality associated with advanced endoscopy procedures. In a closed claims review of out of the operating room procedures, Metzner et al1 found that 32% of all malpractice claims were for GI procedures. The authors cited ERCP procedures as being one of the highest risk procedures (see Anesthesia Abstracts February 2010, Volume 4, Number 2). Inadequate oxygenation and ventilation was the most common cause of mortality. Contributing factors associated with over sedation leading to respiratory depression were ASA 3-5 status (54%), obesity (56%), age > 70 (27%), and use of propofol. Two of these four factors are clinical characteristics of obstructive sleep apnea; obesity and age > 70. I suspect some of the GI patients who died in the closed claims study had obstructive sleep apnea given 43% of the patients in this current study were high risk for obstructive sleep apnea based on the STOP-BANG results.

 

It is not surprising that patients with obstructive sleep apnea required more airway maneuvers and experienced a higher incidence of hypoxemia given these patients sensitivity to sedatives and opioids. It is important to point out that sedation was provided by CRNAs with extensive experience in providing sedation for advanced endoscopy procedures. Therefore, these results may be better than expected from other less experienced anesthesia providers or RNs administering sedation for these procedures in this patient population. Many times ERCP procedures are performed in the prone position, in a dark room, making it challenging to identify and manage airway obstruction. Having providers experienced with these procedures is thus critical to minimizing complications. At my facility we typically send at least two providers to this location because of this very reason.

 

Overall, I thought this was an excellent study which provides further evidence demonstrating the STOP-BANG is a useful screening tool for sleep apnea. Vasu et al2 in 2010 found that the STOP-BANG had a 91.7% sensitivity and 63.7% specificity in predicting postoperative cardiac and pulmonary complications in noncardiac surgery patients (See Anesthesia Abstracts November 2010, Volume 4, Number 11). Therefore, I think anesthesia providers should consider incorporating this tool into their preoperative screening process.

Dennis Spence, PhD, CRNA


1. Metzner J, Posner KL, Domino KB. The risk and safety of anesthesia at remote locations: the US closed claims analysis. Curr Opin Anesthesiol 2009;22: 502-508.

2. Vasu TS, Dogharmji K, Cavallazzi R et al. Obstructive sleep apnea syndrome and postoperative complications: clinical use of the STOP-BANG questionnaire. Arch Otolaryngol Head Neck Surg 2010;136: 1020-1024.


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





Identification of patients at risk for postoperative respiratory complications using a preoperative obstructive sleep apnea screening tool and postanesthesia assessment

Anesthesiology 2009;110:869-876

Gali B, Whalen FX, Schroeder DR, Gay PC, Plevak DJ


Abstract

Purpose The purpose of this study was to determine if a combination of preoperative screening for obstructive sleep apnea and a postanesthesia care unit (PACU) assessment could predict patients at risk for postoperative complications.

 

Background Patients with obstructive sleep apnea are at increased risk for perioperative complications. Therefore, it is essential that patients be identified so that appropriate postoperative management can be planned. Unfortunately, 80% to 90% of patients with obstructive sleep apnea are undiagnosed. ASA guidelines published in 2006 recommended screening patients for obstructive sleep apnea, and to consider prolonged monitoring of patients thought to have moderate to severe obstructive sleep apnea. However, these recommendations were based largely on expert opinion. Knowing how to best screen and manage patients with obstructive sleep apnea in the postoperative period continues to be unclear.

 

One screening tool, called the Sleep Apnea Clinical Score (SACS), has moderate sensitivity (76%) and positive predictive value (77%) in identifying outpatients at high risk for obstructive sleep apnea. An additional screening tool is the oxygen desaturation index (ODI). The ODI is defined as the number of oxygen desaturations > 4% for at least 10 seconds. An ODI of >10 has a 71% to 85% sensitivity and 90% to 95% specificity for detecting obstructive sleep apnea. Additionally, it is possible that obstructive sleep apnea patients who experience frequent respiratory events such as apnea, hypopnea, desaturation, and pain-sedation mismatch in the PACU may be at risk for postoperative complications. (Pain-sedation mismatch is a high pain score and high sedation score.)

 

This study sought to determine if a combination of screening with the SACS and postanesthesia care unit assessment of respiratory events would identify patients at risk for postoperative complications and / or predict those with a higher ODI postoperatively.

 

Methodology This prospective cohort study was carried out between 2005 and 2007 and included 693 patients at a large academic medical center. Patients were enrolled if they were scheduled for an inpatient surgery. Patients without a history of diagnosed obstructive sleep apnea were enrolled. Patients were screened for obstructive sleep apnea using the Flemon’s criteria to establish a SACS score. Patients with a SACS score >15 were categorized as high risk and those with SACS < 15 as low risk. Anesthesia providers were not informed of the SACS score. Choice of anesthesia methods was at the discretion of the anesthesia provider.

 

In the PACU, patients were monitored for apnea, bradypnea, oxygen desaturations (< 90% with nasal cannula), and pain-sedation mismatch. If a patient experienced two or more of these events during the 90 minute PACU period they were admitted overnight to an intermediate care unit for closer observation. Respiratory complications included ICU admission, need for respiratory therapy beyond usual care, noninvasive positive airway pressure, and development of pneumonia. Cardiac complications included a new arrhythmia requiring treatment, and myocardial infarction. Patients were further divided into recurrent PACU event groups. Results were adjusted for baseline demographics (age, BMI, and gender). A P < 0.05 was significant.

 

Result Of the 693 patients, 32% were at high risk for obstructive sleep apnea based on the SACS score. Patients in the high risk group were more likely to be male (86% vs. 43%), have a greater BMI, larger neck circumference, have high blood pressure (81% vs. 38%), and have a higher ASA class (ASA III: 39% vs. 25%) than those in the low risk group (P < 0.001). Surgical procedures were significantly different between the groups, with patients in the low risk group having a higher rate of gynecological (10% vs. 2%) and general abdominal surgery (6% vs. 3%). Urology surgery (24% vs. 11%), and neurosurgery (14% vs. 11%) were more common in the high obstructive sleep apnea risk group (P < 0.001). No differences were reported in the duration of surgery or in the use of regional anesthesia between the two groups.

 

The occurrence of one or more of any type of recurrent PACU event was significantly greater in the high risk group (42% vs. 35%, P = 0.043). Patients at high risk for obstructive sleep apnea had a higher frequency of one or more desaturation events when compared to the low risk group (28% vs. 11%, P < 0.001). No significant difference was found in the frequency of apnea, hypopnea, or pain-sedation mismatch between the two groups.

 

Postoperatively the mean ODI and frequency of patients with an ODI > 10 was higher in those at high risk for obstructive sleep apnea (P < 0.001), and higher in patients who had recurrent PACU events (P < 0.05). The incidence of high ODI remained significant after adjusting for demographic variables.

 

High risk patients were 3.5 times more likely to experience a postoperative respiratory event (P < 0.0001), and 21 times more likely to experience recurrent PACU events (P < 0.001; Figure 1). Postoperative complications were 2.7 times more likely to occur in those at high risk but this association was no longer significant after adjusting for age, gender, and BMI. Postoperative complications were 13.4 times more likely to occur if a patient experienced a recurrent PACU event. In high risk patients who experienced recurrent PACU events (n = 52), the most frequent respiratory complication was need for ICU admission (high risk 27% vs. low risk 8%; Figure 1).

 

 

Figure 1. Incidence of perioperative complications

Figure 1

Note. ICU admission was for a new respiratory indication such as respiratory failure. RT therapy = Patient needed respiratory therapy treatment (i.e., albuteral therapy). CPAP = continuous positive pressure.

 

 

Conclusion The combination of a preoperative Sleep Apnea Clinical Score (SACS) > 15 and recurrent PACU respiratory events was associated with postoperative respiratory complications and a higher incidence of oxygen desaturation events. These tools may be able to identify patients at risk for respiratory complications independent of obstructive sleep apnea risk.

 

Comment

This is one of the few published studies which provided evidence demonstrating an obstructive sleep apnea protocol may help decrease postoperative respiratory complications. I particularly like how this facility has developed some objective PACU criteria which can be used to determine if a patient requires a higher level of monitoring than what can be provided on a surgical ward. Anesthesia providers at many institutions struggle with how to manage and where to send patients with moderate to severe obstructive sleep apnea who require closer observation postoperatively. At my institution we keep inpatients with severe obstructive sleep apnea overnight in our recovery room because we do not have an intermediate step down unit. Also we keep many moderate to severe OSA patients for an extended period of time in our PACU, typically 3+ hours. I think it is essential to develop some sort of policy or guideline for the management of patients with obstructive sleep apnea.

 

This is the second study from this institution that has reported on the use of the SACS obstructive sleep apnea scoring system (see Anesthesia Abstracts June 2009, Volume 3 Number 6). The SACS instrument has a lower sensitivity (76%) compared to other instruments such as the STOP-BANG, which has > 90% sensitivity in identifying those at high risk for moderate to severe obstructive sleep apnea. The SACS scoring system does not include questions on gender, age, BMI, or tiredness, which are included in the STOP-BANG. Not surprisingly, these demographic factors were more common in patients identified as high risk for obstructive sleep apnea in this current study. When age, gender and BMI were controlled for the investigators found that the incidence of postoperative complications was no different between those at high or low risk for obstructive sleep apnea based on the SACS scoring model. I suspect if this study was replicated using the STOP-BANG and a larger sample size the differences may still have been significant.

Dennis Spence, PhD, CRNA


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





Preoperative predictors of difficult intubation in patients with obstructive sleep apnea syndrome

Can J Anesth 2006;53:393-397

Kim JA, Lee JJ


Abstract

Purpose The purpose of this study was to determine if patients with obstructive sleep apnea (OSA) have a higher incidence of difficult intubation when compared to patients without obstructive sleep apnea. The secondary outcome was to compare the severity of obstructive sleep apnea with the incidence of difficult intubation.

 

Background It has been estimated that 4% of males and 2% of females have obstructive sleep apnea. It is speculated that OSA is associated with difficult intubation; however it is unclear if the severity of obstructive sleep apnea, as measured by the Apnea Hypopnea Index (AHI), is predictive of difficult intubation.

 

Methodology This retrospective case-control study included 180 patients. Ninety patients presenting for uvulopalatopharyngoplasty (UPPP) with a diagnosis of obstructive sleep apnea were included in the obstructive sleep apnea group, and 90 patients from the same month’s list of endoscopic sinus surgery were included in a control group. The control group was matched for gender and age (± 2 years).

 

Baseline data included age, height, weight, body mass index (BMI), smoking or alcohol history, history of hypertension or diabetes, AHI score, and the lowest oxygen saturation during an abnormal respiratory event during sleep. Difficult intubation was defined as a Grade III or IV laryngoscopic view, the need for an intubation aid (i.e., intubating stylet, intubating LMA, fiberoptic bronchoscope), or three or more attempts needed to secure the airway. Intubation was completed by one of two anesthesiologists with at least 5 years experience.

 

Statistical and power analyses were appropriate. Patients in the obstructive sleep apnea group were categorized according to AHI as follows:

  • AHI < 40 mild to moderate obstructive sleep apnea
  • AHI 40 to 70 severe obstructive sleep apnea
  • AHI > 70 extremely severe obstructive sleep apnea.

A P value < 0.05 was significant.

 

Result No significant differences were found between patients with obstructive sleep apnea and the control group with regards to gender, age, height, smoking history, alcohol use, or incidence of diabetes. A majority of patients were male (96%), with a mean age of 44 years. Patients with OSA had a significantly higher BMI (27.9 ± 2.9 kg/m2 vs. 25.3 kg/m2, P < 0.001). The incidence of hypertension was higher in the obstructive sleep apnea group (28.9% vs. 12.2%, P = 0.018).

 

The incidence of difficult intubation was 16.6% in the obstructive sleep apnea group and 3.3% in the control group (P < 0.05). Obstructive sleep apnea patients with a difficult intubation had a significantly higher AHI when compared to those without a difficult intubation (67 vs. 50, P = 0.026). There was an association between AHI and the incidence of difficult intubation (P = 0.039). The incidence of difficult intubation was 27.6 % in those with AHI > 70, 19.3% in those with an AHI from 40 to 70, and 3.3% (same as control) in those with AHI < 40 (Figure 1).

 

 

Figure 1. Difficult intubation incidence by OSA severity

Figure 1

Note. Mean AHI presented for each subgroup of OSA patients.

 

 

Conclusion The incidence of difficult intubation can be predicted from the Apnea Hypopnea Index (AHI) in those patients undergoing UPPP procedures. There was an association between obstructive sleep apnea severity and the incidence of difficult intubation. Patients who had an AHI > 40 had the highest incidence of difficult intubation.

 

Comment

This study indicated that there was an association between obstructive sleep apnea severity and the incidence of difficult intubation in those patients undergoing UPPP. UPPP is a commonly performed surgical procedure used to treat obstructive sleep apnea and severe snoring. Every time I take care of a patient presenting for this procedure I always prepare for a potential difficult intubation because the excessive redundant tissue associated with obstructive sleep apnea tends to make visualization of the glottis difficult. This study confirms my clinical experience. These results tell me it is important to know the severity of the obstructive sleep apnea. In this study there was greater than a 19% incidence of difficult intubation if the AHI was > 40.

 

In addition to obstructive sleep apnea being associated with difficult intubation, it is also an independent predictor of impossible mask ventilation (see Anesthesia Abstracts May 2009, Volume 3, Number 5).1 Other factors associated with impossible mask ventilation include neck radiation changes, male gender, Mallampati class III or IV, and presence of a beard. Therefore, if a patient presents for UPPP (or any other surgery) with 3 or more of the predictors I would be very concerned about the ability to ventilate and possibly intubate. To prepare for these cases I would have extra equipment (e.g., Glidescope) and personnel available in the event of a difficult mask ventilation or intubation.

 

Despite the retrospective nature of the study, I think it is an important study which highlights the risks associated with OSA. It is also important to point out that this study was published in 2006, before some of the new indirect video laryngoscopy devices came to market (e.g., Glidescope). Therefore, it is unclear if similar results would be seen if these devices were used. Experience suggests that the incidence of difficult intubation would probably be less. Nonetheless, I think it is still extremely important that anesthesia providers have a healthy respect for the airway and risks associated with obstructive sleep apnea.

Dennis Spence, PhD, CRNA


1. Kheterpal S, Martin L, Shanks AM, Tremper KK. Prediction and outcomes of impossible mask ventilation: review of 50,000 anesthetics. Anesthesiology 2009;110:891-897.


Apnea was defined as cessation of breathing >10 seconds; hypopnea was a 50% reduction in breathing effort with at least a 4% decrease in SaO2. The AHI was the total number of apneic or hypopneic events in one hour.

 

The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





Obstructive sleep apnea is not a risk factor for difficult intubation in morbidly obese patients

Anesth Analg 2009;109:1182-1186

Meligan PJ, Porter S, Max B, Malhotra G, Greenblatt EP, Ochroch EA


Abstract

Purpose This study sought to determine if morbid obesity, obstructive sleep apnea (OSA), and neck circumference were risk factors for difficult intubation in patients undergoing bariatric surgery.

 

Background Mallampati score (MP) and neck circumference have been demonstrated to be predictors of difficult intubation. Some speculate that morbid obesity and obstructive sleep apnea are also risk factors for difficult intubation. Given the increased prevalence of obstructive sleep apnea and use of bariatric surgery to treat obesity, clinicians are likely to encounter higher frequencies of difficult intubations in these patient populations. However, most of the research demonstrating an association between obstructive sleep apnea and difficult intubation is from retrospective studies, which are prone to selection bias. This study sought to determine if OSA, BMI, and neck circumference were risk factors for difficult intubation in patients undergoing bariatric surgery.

 

Methodology This was a prospective observational study of 180 consecutive patients undergoing bariatric surgery. All patients completed a preoperative polysomnography examination to determine the incidence and severity of obstructive sleep apnea. Obstructive sleep apnea severity was defined by the apnea hypopnea index (AHI), which is the number of apneic and hypopneic events per hour of sleep. An AHI of 0-5 indicated no obstructive sleep apnea, 6-20 mild obstructive sleep apnea, 21-40 moderate obstructive sleep apnea, and >40 severe obstructive sleep apnea. All patients had their airway examined by one of the investigators, and the Mallampati class was recorded. In the operating room all patients were “ramped,” ensuring the external auditory meatus was horizontal with the sternal notch. A standardized induction sequence was used for all patients. Induction drugs included propofol, fentanyl, and neuromuscular blockade with vecuronium or succinylcholine. The first three laryngoscopy was attempted by the anesthesia resident, after which the staff anesthesiologist attempted to secure the airway. One of the investigators recorded the Cormack and Lehane grade view on first laryngoscopy without external laryngeal manipulation. All patients underwent bariatric surgery.

 

A difficult intubation was defined as three or more attempts. Difficult laryngoscopy was defined as a grade III or IV view. Ordinal logistic regression models were used to determine the relationship between number of intubation attempts or grade view and the risk factors: gender, age, BMI, OSA, AHI, OSA severity, Mallampati score, neck circumference, and anesthesia resident level of training. A P < 0.05 was considered significant.

 

Result A total of 180 patients completed the study; 78% were female, with an average age of 46, and average BMI of 49.4 ± 7.6. Sixty-eight percent (68%) of patients had obstructive sleep apnea, with a mean AHI of 31 (AHI range 0 to 135). The median obstructive sleep apnea severity was mild. Median Mallampati score was a class II. Average neck circumference was 44 cm. The median laryngoscopy view was a grade 1, and median number of intubation attempts was 1. All patients were intubated within three attempts by the anesthesia resident.

 

Six patients required three or more attempts at laryngoscopy making the difficult intubation rate 3.3%. Fifteen patients (8.3%) had a grade III or IV laryngoscopic view. No relationship was found between obstructive sleep apnea and incidence of difficult intubation (P = 0.09). No relationship was found between BMI, neck circumference, or AHI and either the incidence of difficult intubation or number of intubation attempts. No relationship was found between BMI, AHI, or obstructive sleep apnea and the laryngoscopic view. A Mallampati class III or IV airway was predictive of difficult intubation, as was male gender (P = 0.02). Patients with a larger neck circumference had a poorer grade view (P = 0.02), however they were not difficult to intubate (P = 0.23).

 

Conclusion A Mallampati score of III or IV and male gender were the only predictors of difficult intubation in bariatric surgery patients positioned in the “ramped” position. No relationship was found between the incidence of difficult intubation or difficult laryngoscopy and the presence or severity of obstructive sleep apnea, BMI, or neck circumference.

 

Comment

Morbid obesity and obstructive sleep apnea have been hypothesized to be predictors of difficult intubation and difficult laryngoscopy. In this study the investigators found the opposite, that morbid obesity and sleep apnea were not associated with the difficult intubation or a difficult laryngoscopy. Why the difference? First, the sample included patients undergoing bariatric surgery, with the majority of them being female. Only 23% of the sample was male. In this study the investigators found that male gender was associated with increased difficulty with intubation. Men tend to have larger necks and have a higher BMI, and more severe Obstructive Sleep Apnea when compared to women. Additionally, the median Obstructive Sleep Apnea severity was in the mild range. Other investigators have found an association between severe Obstructive Sleep Apnea (AHI >50) and the incidence of difficult intubation.1 Therefore, I think these results may not be applicable to other surgical populations or in patients with more severe Obstructive Sleep Apnea.

 

The investigators chose to define a difficult intubation differently than previous investigators. Several other studies define a difficult intubation as three or more attempts and/or a Grade III or IV view.1,2 Thus, it is possible that if the investigators had used this definition they may have found more difficult intubations.

 

I was interested to read this study because the investigators reported that obstructive sleep apnea was not associated with a difficult intubation; however the investigators did not report the percent of patients with obstructive sleep apnea who had a difficult intubation. Because the investigators were doing a logistic regression they would have needed 333 to 1000 subjects to identify 1 or more risk factors for difficult intubation. Therefore, I think this study was significantly underpowered. Thus I would view these results as preliminary, and not assume that a patient presenting for bariatric surgery who has a history of moderate to severe obstructive sleep apnea is not at risk for a difficult intubation.1,2

 

So what are the important take home points from this study? First, a thorough airway examination and preparation is essential. Patients presenting for bariatric surgery should be ramped, or have the head of the bed tilted up 25 degrees (see Anesthesia Abstracts Volume 3 Number 3, March 2009).3 Always be prepared for a difficult airway. Have a video laryngoscopy device such as a Glidescope or McGrath available. It is better to assume the bariatric patient may be a difficult intubation. This will keep you out of trouble.

Dennis Spence, PhD, CRNA


1. Lee SJ, Lee JM, Kim TS, Park YC. The relationship between the predictors of obstructive sleep apnea and difficult intubation. Korean J Anesthesiol 2011;60: 173-178.

2. Kim JA, Lee JJ. Preoperative predictors of difficult intubation in patients with obstructive sleep apnea syndrome. Can J Anesth 2006;53: 393-397.

3. Rao SL, Kunselman AR, Schuler GH, DesHarnais S. Laryngoscopy and tracheal intubation in the head-elevated position in obese patients: a randomized, controlled, equivalence trial. Anesth Analg 2008;107: 1912-1918.


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





The relationship between the predictors of obstructive sleep apnea and difficult intubation

Korean J Anesthesiol 2011;60:173-178

Lee SJ, Kim TS, Park YC


Abstract

Purpose The purpose of this study was to identify predictors of difficult intubation in patients with obstructive sleep apnea (OSA) who were presenting for palatal muscle resection surgery.

 

Background Obstructive sleep apnea is characterized by repetitive, partial or complete obstruction of the pharynx during sleep. It is associated with the development of severe complications such as hypertension, pulmonary hypertension, cardiac arrhythmias, and congestive heart failure. Continuous positive airway pressure therapy (CPAP) is first line therapy for obstructive sleep apnea; however some patients may not tolerate or fail CPAP therapy. Thus, some patients may require palatal muscle resection surgery to treat their obstructive sleep apnea. Unfortunately, patients with obstructive sleep apnea may be at increased risk for difficult mask ventilation and intubation due to an excessive amount of soft tissue. Investigators in this study sought to determine what factors predict difficult intubation in Korean patients with a history of obstructive sleep apnea who were presenting for palatal muscle resection surgery.

 

Methodology This was a cohort study of 115 ASA I and II patients with a diagnosis of obstructive sleep apnea who were undergoing palatal muscle resection surgery. Prior to surgery, all patients completed an overnight polysomnography study and the apnea hypopnea index (AHI) was recorded. Mild sleep apnea was defined as an AHI of between 5 and < 25, moderate an AHI of ≥ 25 and < 50, and severe as ≥ 50. If the patient’s blood pressure at the time of the sleep study was SBP >140 mm Hg and/or DBP > 90 for 3 measurements, they were considered to have hypertension. Preoperatively, an airway exam was completed. A standardized induction sequence was used for all patients and all intubations were performed by a skilled provider. Patients were positioned in a sniffing position and a Macintosh 3 blade was used to intubate all patients.

 

Data collection included sleep study results, demographic data, and intubation results. Obstructive sleep apnea was categorized using the AHI as mild or moderate (AHI < 50) or severe (AHI ≥ 50). Investigators recorded baseline demographic data, incidence of hypertension, Mallampati class, and neck circumference. During intubation the grade view was recorded using the Cormack and Lehane grading scale. Logistic regression was used to identify predictors of difficult intubation. A P < 0.05 was considered significant.

 

Result Of the 115 male obstructive sleep apnea patients, 80% were easy intubations and 20% were difficult intubations. No significant differences were found in age, BMI, hypertension incidence, or Mallampati class between the two groups (Table 1). In the difficult intubation group 74% had a Mallampati class III or IV airway as compared to 55% in the easy intubation group (P = NS). Neck circumference was significantly larger in the difficult intubation group (Table 1; P = 0.014). In the difficult intubation group 70% had a neck circumference ≥ 40 cm as compared to 35% in the easy intubation group (P = 0.004). The AHI was almost 20 points higher in the difficult intubation group as compared to the easy intubation group (49.3 vs. 28.9, P = 0.008). Almost twice as many patients who had a difficult intubation were classified as having severe sleep apnea (AHI ≥ 50) when compared to those with an easy intubation (61% vs. 32%, P = 0.015; Table 1).

 

Logistic regression revealed that neck circumference and AHI were predictors of difficult intubation (P < 0.05). Patients with a neck circumference ≥ 40 cm were 1.76 times more likely to be a difficult intubation (95% CI: 1.29, 2.41, P < 0.0001). Similarly, patients with an AHI ≥ 50 were 1.124 times more likely to be a difficult intubation (95% CI: 1.04, 1.22, P = 0.005).

 

 

Table 1. Demographics

 

Difficult Intubation

Easy Intubation

P value

Age

38.8 ± 11.7

38.1 ± 12.3

NS

BMI

27.3 ± 2.4

26.9 ± 3.2

NS

Hypertension

43%

42%

NS

MP I or II

MP III or IV

26.1%

73.9%

44.6%

55.4%

NS

Neck circumference (cm)

< 40

≥ 40

43.9 ± 2.5

30%

70%

38.8 ± 3.7

65%

35%

0.014

0.004

AHI

< 50

≥ 50

49.3 ± 19.5

39%

61%

28.9 ± 18

68%

32%

0.008

0.015

Note. MP = Mallampati classification.

 

 

Conclusion Male patients with a history of obstructive sleep apnea presenting for palatal muscle resection with larger necks (≥ 40 cm) and more severe sleep apnea (AHI ≥ 50) were more likely to be difficult to intubate. If patients present with these conditions anesthesia providers should be prepared for a difficult intubation.

 

Comment

I found this to be an interesting study because it examined predictors of difficult intubation in an Asian population with obstructive sleep apnea. The investigators examined patients who had failed conservative therapy for obstructive sleep apnea (i.e., CPAP) and were scheduled for palatal muscle resection surgery. In this study 37% of the patients had severe obstructive sleep apnea, as defined as an AHI > 50. Many investigations published in the United States have used cut-offs for severe obstructive sleep apnea as an AHI of 30 or 40.1,2 So this sample may only apply to patients with more severe obstructive sleep apnea (AHI > 50).

 

Not surprisingly, the investigators found the incidence of difficult intubation was rather high, at 20%. They also confirmed that patients with severe obstructive sleep apnea and large necks (> 40 cm) may be more difficult to intubate. While not statistically significant, a larger proportion of the patients who actually were difficult to intubate (74% vs. 55%) were classified as potential difficult intubations preoperatively (Mallampati class III or IV). It would have been interesting to see if there were differences in other airway examination results between those with easy or difficult intubations, such as thyromental distance or mouth opening. When evaluating a patient for a potential difficult airway it is essential to do a thorough airway examination.

 

There are several limitations to this study. Given that the incidence of difficult intubation was only 20%, it is not surprising that they were only able to identify two predictors in their logistic regression model. I suspect if they would have had a larger sample size that Mallampati class III or IV would have been identified as a predictor of difficult intubation. I also wonder if the use of a Macintosh size 3 curved blade may have falsely elevated the incidence of difficult intubation. In my experience, I find that in male patients, especially those with obstructive sleep apnea, I need to use a longer blade to obtain a better view of the glottis. I also would have liked to have known if any airway adjuncts were required (i.e., bougie).

 

I think the important take home message of this investigation is that AHI and neck circumference should be considered potential predictors of difficult intubation in male patients known to have obstructive sleep apnea. Anytime an anesthesia provider takes care of a patient with moderate to severe obstructive sleep apnea, they should be prepared to manage a difficult intubation. Other devices and airway adjuncts should be readily available, and strong consideration should be given to performing an awake fiberoptic intubation in a patient with severe obstructive sleep apnea, a large thick neck, and other factors of a potential difficult airway.

Dennis Spence, PhD, CRNA


1. Chung F et al. STOP questionnaire: a tool to screen patients for obstructive sleep apnea. Anesthesiology 2008;108:812-821.

2. Gross et al. Practice guidelines for the perioperative management of patients with obstructive sleep apnea: a report by the American Society of Anesthesiologists Task Force on Perioperative Management of Patients with Obstructive Sleep Apnea. Anesthesiology 2006;104:1081-1093.


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





Postoperative complications in patients with obstructive sleep apnea syndrome undergoing hip or knee replacement: a case-control study

Mayo Clin Proc 2001;76:897-905

Gupta RM, Parvizi J, Hanssen AD, Gay P


Abstract

Purpose The purpose of this study was to determine if patients with known or suspected obstructive sleep apnea (OSA) undergoing lower extremity joint replacement had increased rates of postoperative complications when compared to control patients without obstructive sleep apnea.

 

Background Patients with obstructive sleep apnea who present for surgery are at increased risk for perioperative morbidity and mortality. Patients with obstructive sleep apnea are at risk for early and late nocturnal hypoxemia after elective surgery. Some studies have found that patients with obstructive sleep apnea who underwent abdominal surgery experienced significant episodic nocturnal oxygen desaturations of < 85%. These findings reinforce the importance of identifying patients at risk for obstructive sleep apnea preoperatively so plans can be made to decrease complications.

 

Methodology This was a retrospective case-control study of patients with clinically suspected or diagnosed obstructive sleep apnea who underwent total joint replacement between the years 1995 and 1998. The Mayo Clinic Total Joint Registry and Sleep Center databases were queried to identify patients. The diagnosis of obstructive sleep apnea was determined by physical signs and symptoms in addition to a respiratory disturbance index (RDI) of ≥ 5 on polysomnography, or highly abnormal pattern of activity on an overnight home oximetry study suggestive of obstructive sleep apnea. Patients with obstructive sleep apnea who had their surgery within 3 years before or any time after their diagnosis of obstructive sleep apnea were included. Patients without objective data to confirm obstructive sleep apnea were excluded.

 

The control group was matched on age, sex, operative side, type of operation, mode of fixation of joint components, year of operation, surgeon, and type of anesthesia. Data collected from the medical records included demographics, type of comorbidities, sleep disorders, preanesthesia evaluation results, and postoperative course. Total postoperative opioid consumption, types of therapeutic interventions, need for ICU admission, use of CPAP, and length of stay were recorded. Postoperative complications are shown in Table 1.

 

 

 

Table 1. Postoperative Complications

Reintubation

 

Acute Hypercapnia

PaCO2 > 45 mm Hg on blood gas obtained for clinical concerns and/or need for CPAP.

Episodic Desaturation

SPO2 < 90% and > 4% reduction from last recorded value is association with witnessed apnea.

Arrhythmia

Events associated with clinical symptoms requiring treatment or additional monitoring.

Myocardial Ischemia

 

Myocardial Infarction

 

Delirium

As noted by caregivers

Note. Serious complications were defined as complications necessitating transfer to the ICU for cardiac events or urgent respiratory support with need for intubation or CPAP.

 

 

Investigators compared the incidence of complications between obstructive sleep apnea and controls patients. They also compared results between those with diagnosed and undiagnosed obstructive sleep apnea. Investigators also compared complication rates between obstructive sleep apnea patients who were using home CPAP and those who were not using home CPAP. A P < 0.05 was significant.

 

Result A total of 202 subjects were included in the study; 101 in the obstructive sleep apnea group and 101 in the control group. In the obstructive sleep apnea group, 36 were undiagnosed and 65 were diagnosed at the time of surgery. Of those patients diagnosed with obstructive sleep apnea, 51% were using home CPAP, and 49% were either noncompliant with CPAP (n = 11), or were not prescribed CPAP (n = 21).

 

No significant differences were found in baseline demographics. The average age was approximately 68 years in both groups. A majority of subjects in the obstructive sleep apnea and the control group were male (69.3%). Patients in the obstructive sleep apnea group had a higher BMI compared to the control group, however this was not statistically significant (34 vs. 30). Likewise the incidence of hypertension was higher in the obstructive sleep apnea group, though this difference was not statistically significant (58% vs. 48%). Opioid consumption was similar between the groups (P = NS). Within the obstructive sleep apnea group opioid consumption was similar between those who developed complications and those who did not.

 

The incidence of postoperative complications was significantly higher in the obstructive sleep apnea group (39% vs. 18%, P = 0.001; Figure 1). The incidence of serious complications was higher in the obstructive sleep apnea group compared to the control group (24% vs. 9%, P = 0.004). The incidence of planned and unplanned ICU admissions was significantly higher in the obstructive sleep apnea group (P = 0.003; Figure 1). Patients with obstructive sleep apnea stayed 1.7 days longer, on average, when compared to the control group (6.8 ± 2.8 vs. 5.1 ± 4.1 days, P = 0.007). A majority of the complications in the obstructive sleep apnea group occurred within the first 72 hours (92%); with most of these patients experiencing a complication within the first 24 hours (64%).

 

 

Figure 1. Incidence of Postoperative Complications

Figure 1

Note. Serious complications were defined as complications necessitating transfer to the ICU for cardiac events or urgent respiratory support with need for intubation or CPAP.

 

 

Twenty patients in the obstructive sleep apnea group had an unplanned ICU admission compared to 6 in the control group. Two patients in the obstructive sleep apnea group required reintubation in the PACU for severe hypercapnia. Another 2 patients in the obstructive sleep apnea group were admitted for hypercapnia without reintubation, 1 for myocardial infarction, 5 for cardiac ischemia, 6 for severe hypoxemia, and 4 for arrhythmias. Of the 6 in the control group with an unplanned ICU admission, 3 were for cardiac ischemia, 1 for arrhythmia, 1 for myocardial infarction, and 1 for postoperative hemorrhage. No patient in the control group was admitted to the ICU for respiratory complications (Figure 2).

 

Subgroup analysis comparing patients with undiagnosed and diagnosed obstructive sleep apnea found that the incidence of serious complications was significantly higher in the undiagnosed obstructive sleep apnea group (44% vs. 27%), as were total (32% vs. 3%) and unplanned ICU admissions (28% vs. 3%) (P < 0.05). Hospital length of stay was approximately 2 days longer in the undiagnosed OSA group (P = 0.03).

 

Figure 2. Type of Postoperative Complications

Figure 2

Note. Cardiac events included arrhythmias, myocardial ischemia, and myocardial infarction. No significant differences between groups found for any complication (P = NS).

 

 

Conclusion Patients diagnosed with obstructive sleep apnea either before or after total joint replacement had a significantly higher incidence of postoperative complications. The incidence of severe postoperative complications was the highest in patients with obstructive sleep apnea who were not using CPAP prior to their surgery.

 

Comment

This study is one of the earlier investigations which examined the association between obstructive sleep apnea and postoperative complications. The novel part of this study was that the investigators included patients in the obstructive sleep apnea group if they had been diagnosed either before or after their surgery. The investigators found that patients with obstructive sleep apnea, especially those who were not on home CPAP, had the highest rate of serious complications. Almost a quarter of patients with obstructive sleep apnea suffered a serious complication. Those who were not on home CPAP included both those with a diagnosis of obstructive sleep apnea, but who were either noncompliant or not on CPAP, as well as those who were undiagnosed at the time of their surgery.

 

The investigators chose to combine both cardiac and respiratory complications into the serious complications category. However, a majority of the complications were respiratory, such as episodic hypoxemia. When I reanalyzed their results, I found a significantly higher incidence of respiratory complications in the obstructive sleep apnea group as compared to the control group (28% vs. 10%, P = 0.019). However, the incidence of cardiac complications was similar between the obstructive sleep apnea and control group (16% vs. 9%, P = 0.19). These results are not surprising, given patients with obstructive sleep apnea are more sensitive to anesthetic agents and opioids, and thus more prone to worsening of their airway obstructive symptoms.

 

During the first 24 hours postoperatively, anesthetic agents and opioids lead to decreased rapid eye movement (REM) sleep. Patients with obstructive sleep apnea experience more obstructive symptoms during REM sleep because this is the time when pharyngeal muscle tone is the lowest.1 There is a rebound of REM sleep within 48 to 72 hours. This can explain the persistent respiratory complications that occurred up to 72 hours after surgery in this study.

 

There are several limitations to this study. First, it was a retrospective case-control study. Retrospective studies may underreport the actual incidence of complications. Case-control studies are prone to selection bias, which means the sample may not be representative of all patients with obstructive sleep apnea. The investigators tried to compensate for this issue by including patients diagnosed with obstructive sleep apnea before or after their surgery; however, this can create problems with interpretation of their results. The problem is that providers may manage patients differently if they know they have a diagnosis of sleep apnea. Thus it is not surprising that respiratory complications were more common in those patients who had undiagnosed obstructive sleep apnea at the time of their surgery.

 

It is important to point out this study included patients who had surgery between 1995 and 1998. The awareness and understanding of the perioperative implications of obstructive sleep apnea were much less during this time frame. It was not until 2006 when the American Society of Anesthesiologists published the practice guidelines for management of patients with obstructive sleep apnea.2 Therefore, readers should view these results in the context in which the study was conducted. Nonetheless, I still think the results are relevant since more recent studies have found respiratory complications such as hypoxemia are the most common complications experienced by obstructive sleep apnea patients during the postoperative period.3

Dennis Spence, PhD, CRNA


1. Horner RL. Respiratory motor activity: influence of neuromodulators and implications for sleep disordered breathing. Can J Physiol Pharmacol 2007;85: 155-165.

2. Gross et al. Practice guidelines for the perioperative management of patients with obstructive sleep apnea: a report by the American Society of Anesthesiologists Task Force on Perioperative Management of patients with obstructive sleep apnea. Anesthesiology 2006;104: 1081-93.

3. Memtsoudis S et al. Perioperative pulmonary outcomes in patients with sleep apnea after noncardiac surgery. Anesth Analg 2011;112: 113-121.


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





Postoperative complications in patients with obstructive sleep apnea: a retrospective matched cohort study

Can J Anesth 2009;56:819-828

Liao P, Yegneswaran B, Vairavanathan S, Zilberman P, Chung F


Abstract

Purpose The purpose of this study was to determine if obstructive sleep apnea (OSA) is a risk factor for postoperative complications.

 

Background Up to 26% of the population may have obstructive sleep apnea. These patients’ upper airway muscles are more sensitive to anesthetic agents and neuromuscular blocking agents. This may further exacerbate airway obstruction in the postoperative period. Recent studies suggest postoperative nocturnal hypoxemia is common in healthy patients undergoing surgery. Patients with obstructive sleep apnea may experience more severe respiratory complications postoperatively. The investigators hypothesized that obstructive sleep apnea is a risk factor for the development of postoperative complications.

 

Methodology The investigators conducted a retrospective matched cohort study of 240 patients with a diagnosis of obstructive sleep apnea and a matched cohort of 240 without obstructive sleep apnea. Adult patients undergoing elective surgery at an academic medical center were selected from the hospital administrative databases. Patients were excluded if they had upper airway surgery. The control group was matched based on gender, age, same type of surgery, and < 5 years between the surgery dates.

 

The primary outcome of this study was the incidence of postoperative complications. Statistical and power analysis were appropriate. Logistic regression was used to determine what factors were predictive of postoperative complications after controlling for confounding variables. A P < 0.05 was significant.

 

Result No significant differences were reported in the age, gender, or type of surgery. The average age was 57 ± 13 years. Patients with obstructive sleep apnea had a higher incidence of co-existing diseases including obesity, hypertension, gastroesophogeal reflux disease, diabetes, hypothyroidism, asthma, and chronic obstructive pulmonary disease (P < 0.05). In the obstructive sleep apnea group 64% were ASA III or IV compared to 41% in the control group (P < 0.05). The obstructive sleep apnea group also had a higher incidence of New York Heart Association classification III or IV compared to the non-OSA group (15.3% vs. 6.8%; P = 0.05). Continuous positive airway pressure (CPAP) was used by 63% of patients in the obstructive sleep apnea group.

 

Difficult intubation was defined as a grade III or IV view on laryngoscopy and requiring > 2 attempts. The incidence of difficult intubation was twice as high in the obstructive sleep apnea group (20% vs. 10%, P = 0.003). The type of anesthetic technique was similar between the two groups. No significant differences were found in postoperative opioid consumption between the two groups.

 

Postoperative complications were more common in obstructive sleep apnea patients. Patients in the obstructive sleep apnea group were almost two times more likely to experience a postoperative complication compared to the control group (44% vs. 28%, P < 0.01; Figure 1). The most common complications were respiratory (33% vs. 22%, P = 0.01). Hypoxemia with SaO2 < 90% was twice as common in patients with obstructive sleep apnea compared to control patients (17% vs. 8%). Postoperative complications occurred more often in obstructive sleep apnea patients after they were transferred to the ward (25% vs. 16%). In the obstructive sleep apnea group, 23% required prolonged oxygen therapy compared to 15% in the control group (P < 0.05). In the obstructive sleep apnea group, 13% compared to 6% of patients in the control group required prolonged monitoring (P < 0.01). Twenty seven percent (27%) of patients with obstructive sleep apnea who were not on home CPAP required postoperative CPAP secondary to hypoxemia. These patients experienced the highest rate of postoperative complications.

 

Two patients in the obstructive sleep apnea group and one in the control group experienced a cardiac arrest. Of the two obstructive sleep apnea patients, one cardiac arrest was associated with a difficult intubation. The other suffered a cardiac arrest after extubation during a difficult re-intubation attempt. The control patient who experienced a cardiac arrest had a myocardial infarction.

 

 

Figure 1. Perioperative and postoperative events/complications

Figure 1

 

Conclusion This retrospective matched cohort study found that patients with a diagnosis of obstructive sleep apnea had an increased incidence of respiratory complications. The most common complication was severe oxygen desaturation with a SaO2 ≤ 90%. Anesthesia providers should screen all patients for obstructive sleep apnea given their increased risk of respiratory complications.

 

Comment

This study indicates that patients with Obstructive Sleep Apnea are at greater risk for perioperative complications. In this study, patients with Obstructive Sleep Apnea were sicker and required more intensive monitoring and therapy postoperatively. While the investigators could not determine the severity of Obstructive Sleep Apnea, they speculated that a majority of the patients had moderate to severe Obstructive Sleep Apnea, given 63% of them were on home CPAP. Thus these results may not apply to patients with mild Obstructive Sleep Apnea.

 

One important finding of this study was that patients with Obstructive Sleep Apnea had a significantly higher rate of difficult intubation than those without Obstructive Sleep Apnea. What I found scary was that two of these patients suffered a cardiac arrest secondary to problems with airway management; one during induction and the other after extubation. This latter finding reinforces the point that anesthesia providers must have equipment available for a difficult intubation in a patient with Obstructive Sleep Apnea both at the beginning and end of the case.

 

Results of this study should be viewed cautiously because it was retrospective. There is the possibility of coding errors which could lead to inaccuracies in the results. Therefore, one should only consider Obstructive Sleep Apnea is associated with postoperative respiratory complications, rather than being a cause of complications. Trying to determine that Obstructive Sleep Apnea causes postoperative complications is difficult because the disease interacts with many other comorbidities. For example a pre-existing history of stroke was the strongest predictor of a postoperative complication. It is possible that a history of stroke and Obstructive Sleep Apnea significantly increases the risk of complications because many of these patients will be obese with underlying cardiovascular disease and hypertension. Nonetheless, I think these results are important because other studies have found Obstructive Sleep Apnea is associated with postoperative respiratory complications.1

Dennis Spence, PhD, CRNA


1. Vasu TS, Dogharmji K, Cavallazzi R et al. Obstructive sleep apnea syndrome and postoperative complications: clinical use of the STOP-BANG questionnaire. Arch Otolaryngol Head Neck Surg 2010;136: 1020-1024.


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011





Perioperative pulmonary outcomes in patients with sleep apnea after noncardiac surgery

Anesth Analg 2011;112:113-121

Memtsoudis S, Liu SS, Ma Y, Chiu YL, Walz JM, Gaber-Baylis LK, Mazumdar M


Abstract

Purpose The purpose of this study was to determine if obstructive sleep apnea (OSA) was an independent risk factor for perioperative pulmonary complications after noncardiac surgery.

 

Background Patients with obstructive sleep apnea are at increased risk for postoperative respiratory complications. There are published guidelines for safe perioperative management of patients with obstructive sleep apnea. However, these guidelines are largely based on small sample sizes or experiences from single academic centers. To date there have been no large published studies evaluating outcomes in patients with obstructive sleep apnea on a national level.

 

The investigators hypothesized that obstructive sleep apnea was an independent risk factor for postoperative pulmonary complications. If this hypothesis is confirmed, this might provide evidence to support increased intensive monitoring and development of strategies to prevent complications in patients with obstructive sleep apnea.

 

Methodology Data from the National Inpatient Sample (NIS) was obtained commercially from the Hospital Cost and Utilization Project. The NIS is a large inpatient discharge database. The sample consisted of data on all lower extremity joint arthroplasty and general surgical procedures in the NIS database between 1998 and 2007. Patients with obstructive sleep apnea were identified based on appropriate ICD-9 codes (International Classification of Diseases, 9th Edition). Postoperative respiratory complications were identified using the ICD-9 code. They included:

  • aspiration pneumonia
  • adult respiratory distress syndrome (ARDS)
  • pulmonary embolism (PE)
  • need for intubation and postoperative mechanical ventilation

Patients with an obstructive sleep apnea diagnosis were matched with a control group without obstructive sleep apnea using the propensity scoring method. Statistical analysis was appropriate.

 

Result The investigators identified 3,441,262 entries for general surgery and 2,610,441 for orthopedic procedures performed between 1998 and 2007 in the USA (total 6,051,703). The prevalence of obstructive sleep apnea in the general surgery population was 1.4%. In the orthopedic surgery population it was 2.5%. The prevalence of obstructive sleep apnea almost doubled in both samples from 1998 to 2007. Orthopedic patients with obstructive sleep apnea were more frequently males with a younger age when compared to general surgery patients. Overall males had the highest prevalence of obstructive sleep apnea in both surgical populations. The comorbidity burden was higher in patients with obstructive sleep apnea. The prevalence of obesity in general surgery patients with obstructive sleep apnea was 23.8% vs. 4.3% in patients without obstructive sleep apnea. Likewise, orthopedic surgery patients with obstructive sleep apnea had a 30% prevalence of obesity as compared to 6% in non-obstructive sleep apnea patients.

 

The odds of developing postoperative pulmonary complications were significantly higher in patients with obstructive sleep apnea in both general and orthopedic surgery populations (Table 1 and Figures 1 and 2). The most frequent pulmonary complication was need for postoperative intubation. General surgery patients with obstructive sleep apnea were two times more likely to require postoperative intubation. Orthopedic surgery patients with obstructive sleep apnea were five times more likely to require intubation. Pulmonary Embolism was more frequent after orthopedic surgery in obstructive sleep apnea patients compared to controls. However, the incidence of Pulmonary Embolism was slightly lower in general surgery patients with obstructive sleep apnea compared to controls.

 

 

 

Table 1. Odds of Postoperative Pulmonary Complications in Obstructive Sleep Apnea Patients

General surgery

Aspiration pneumonia

ARDS

PE

Intubation/mechanical ventilation

 

1.37 (1.33-1.41)

1.58 (1.54-1.62)

0.90 (0.84-0.97)

1.95 (1.91-1.98)

Orthopedic

Aspiration pneumonia

ARDS

PE

Intubation/mechanical ventilation

 

1.41 (1.35-1.47)

2.39 (2.28-2.51)

1.22 (1.15-1.29)

5.20 (5.05-5.37)

Note. Results are odds ratio (95% confidence interval). All are significant (P < 0.05).

 

 

Figure 1. Incidence of postoperative pulmonary complications 

Figure 1

Note: *OSA = Obstructive Sleep Apnea, ARDS = Adult Respiratory Distress Syndrome, PE = Pulmonary Embolism

 

 

Figure 2. Incidence of postoperative pulmonary complications

Figure 2

Note: *OSA = Obstructive Sleep Apnea, ARDS = Adult Respiratory Distress Syndrome, PE = Pulmonary Embolism

 

Conclusion Using a large national database, the investigators were able to demonstrate that obstructive sleep apnea was an independent predictor of postoperative pulmonary complications after general and orthopedic surgery. This information provides the evidence needed to support increased utilization of resources, such as intensive monitoring and development of strategies to prevent and treat complications in patients with obstructive sleep apnea.

 

Comment

This is the largest study to date analyzing the incidence of complications after noncardiac surgery in patients with OSA. These study results confirm what other investigators have found; that OSA is associated with increased risk of postoperative pulmonary complications.

 

It is important to point out that estimates of the prevalence of obstructive sleep apnea include only those who have been diagnosed. These estimates do not account for the 20-30% who present for noncardiac surgery with undiagnosed obstructive sleep apnea. The good thing is that the investigators found that the prevalence of OSA increased 2-fold from 1998 to 2007, presumably due to increased awareness and diagnosis. Unfortunately, the problem is only going to get worse as our population continues to become more obese. The important take home message is that anesthesia providers need to have a low threshold of suspicion that a patient may have undiagnosed obstructive sleep apnea, and plan the anesthetic and postoperative management accordingly.

 

A limitation of this study was the inability to collect clinical information to determine the severity of obstructive sleep apnea or why patients with obstructive sleep apnea had increased pulmonary complications. The authors speculated that complications such as aspiration pneumonia and ARDS may have been associated with the increased need for postoperative intubation and mechanical ventilation. It may also be that anesthesia providers choose to leave patients with obstructive sleep apnea intubated postoperatively because of airway concerns.

 

In closing, I believe these results are important because they allow anesthesia providers to predict what potential complications may occur in patients with obstructive sleep apnea. It also provides evidence supporting the need to develop management protocols that provide for closer postoperative observation of patients with obstructive sleep apnea.

Dennis Spence, PhD, CRNA


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2011 Anesthesia Abstracts · Volume 5 Number 9, September 30, 2011