ISSN NUMBER: 1938-7172
Issue 6.10 VOLUME 6 | NUMBER 10

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, FAAN
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 2012

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

AIRWAY
Effects of muscle relaxants on mask ventilation in anesthetized persons with normal upper airway anatomy
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EQUIPMENT & TECHNOLOGY
Stroke volume variation as a guide to fluid administration in morbidly obese patients undergoing laparoscopic bariatric surgery
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GENERAL
Intraoperative neuromuscular monitoring site and residual paralysis
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OBSTETRIC ANESTHESIA
Risk factors for failed conversion of labor epidural analgesia to cesarean delivery anesthesia: a systematic review and meta-analysis of observational studies
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PEDIATRIC ANESTHESIA
Comparison of 2 cuff inflation methods before insertion of laryngeal mask airway for safe use without cuff manometer in children
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RESPIRATION & VENTILATION
Society for ambulatory anesthesia consensus statement on preoperative selection of adult patients with obstructive sleep apnea scheduled for ambulatory surgery
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Airway
Effects of muscle relaxants on mask ventilation in anesthetized persons with normal upper airway anatomy

Anesthesiology 2012;117:487-93

Ikeda A, Isono S, Sato Y, Yogo H, Sato J, Ishikawa T, Nishino T


Abstract

 

Purpose The purpose of this study was to examine the effects of muscle relaxants on tidal volume during pressure-controlled ventilation before and after the administration of succinylcholine or rocuronium in healthy patients undergoing elective surgery with general anesthesia. The authors hypothesized that either rocuronium or succinylcholine would both improve face mask ventilation.

 

Background Many anesthesia providers have been taught to confirm the ability to mask ventilate a patient prior to administering a muscle relaxant. However, there is little scientific evidence to support this principal. Several studies have examined the effects of depolarizing and nondepolarizing neuromuscular blocking agents on face mask ventilation. With rocuronium, one study found its administration did not worsen or improve face mask ventilation. On the contrary, other studies have demonstrated that succinylcholine improves face mask ventilation, even in patients with poor glottic views (grade III or IV). Unfortunately, previous studies did not examine the factors that influence airway patency during face mask ventilation. Furthermore, nondepolarizing agents cause progressive muscle paralysis, whereas depolarizing agents such as succinylcholine cause all striated muscles to contract and may dynamically change upper airway patency and thoracic compliance.

 

Methodology Forty-two consecutive patients undergoing elective surgery requiring general anesthesia were enrolled in this study to determine the effects of rocuronium or succinylcholine on tidal volume after induction of anesthesia. Patients with severe comorbidities, allergies to muscle relaxants, upper airway structural abnormalities, difficult mask fit, full dentures, or suspected difficult mask ventilation were excluded. If patients had two or more risk factors on the STOP-BANG questionnaire they were excluded. Patients were allocated to receive either rocuronium or succinylcholine so that they were matched by age, gender, and body mass index.

 

After 3 minutes of preoxygenation, anesthesia was induced with fentanyl 100-150 µg and a target controlled infusion of propofol was set to achieve a concentration of 3-4.5 µg/mL. Patients were hyperventilated to achieve an end tidal CO2 < 35 mm Hg. After confirming the absence of spontaneous ventilation, a custom-made face mask was used to separately measure the tidal volume from the oral and nasal routes. A bi-level positive-pressure ventilator was set to a respiratory rate of 16 per minute with an I:E ratio of 0.33. Inspiratory and expiratory pressures were adjusted to maintain a tidal volume of 2 mL/kg and peak inspiratory pressure of < 18 cm H2O. The head and mandible were maintained in a neutral position. After confirming stable ventilation, patients were either administered rocuronium 0.6 mg/kg or succinylcholine 1 mg/kg. Respiratory variables were measured continuously until complete paralysis (no train of four response) or 60 seconds after succinylcholine administration. Investigators compared differences in the total, oral, and nasal tidal volumes before and after administration of the muscle relaxant. They also compared the time to the minimum and maximum tidal volume after succinylcholine administration. Continuous endoscopic observation of the oral airway was completed in 6 patients who received succinylcholine. Investigators used paired t-tests to compare results. A P < 0.05 was significant.

 

Result There were 14 patients who received rocuronium and 17 who received succinylcholine. An additional 6 patients had endoscopic examinations of their airways after succinylcholine administration. No significant differences were found in nasal, oral, or total tidal volumes before or after rocuronium administration (Figure 1). During the interval between succinylcholine administration and complete paralysis, the mean oral route tidal volume significantly increased (P = 0.002), whereas there was a decrease in mean nasal route tidal volume (P = NS). However, after complete paralysis with succinylcholine nasal tidal volume increased 0.4 mL/kg, oral tidal volume increased 0.9 mL/kg, and total tidal volume increased 1.2 mL/kg (P < 0.05; Figure 2). At the time of complete paralysis, total tidal volume increased 30%, with the oral route increasing to a much greater extent compared to the nasal route (64% vs. 15%).

 

Figure 1. Comparison of Tidal Volume after Rocuronium Administration

Figure 1

Note: Comparisons are between the control and interval or paralysis time periods. Interval was the mean tidal volume of all breaths during the interval between the injection of rocuronium and confirmation of complete paralysis (absence of train of four). P values are obtained by comparing to control condition.

 

 

 

Figure 2. Comparison of Tidal Volume after Succinylcholine Administration

Figure 2

Note: Comparisons are between the control and interval or paralysis time periods. Interval was the mean tidal volume of all breaths during the interval between the injection of succinylcholine and confirmation of complete paralysis (60 sec after injection). P values are obtained by comparing to control condition.

 

The onset of tidal volume changes after succinylcholine occurred approximately 23 seconds after administration in both the oral and nasal routes. The time to minimum tidal volumes occurred approximately 31 seconds after administration in both routes. However, the time to maximum tidal volume was earlier by the oral route (35 vs. 50 seconds, P = 0.001). These changes indicate succinylcholine fasciculations may preferentially increase tidal volume through the oral airway. Endoscopic examination confirmed dilation of the oral airway during pharyngeal fasciculations.

 

Conclusion Rocuronium did not worsen face mask ventilation. However, there was a 30% improvement in face mask ventilation following succinylcholine administration. Improvements in face mask ventilation during succinylcholine administration were primarily due to increases in oral tidal volumes. These findings support the hypothesis that in healthy patients with normal airway anatomy, succinylcholine improves face mask ventilation (i.e., no history of obstructive sleep apnea).

 

Comment

It was ingrained in me from the beginning of my anesthesia training that after induction of anesthesia I had to confirm mask ventilation prior to giving a muscle relaxant. As a student I never questioned this practice and probably continued it for a number of years after graduating. However, as I became more experienced (and confident) I started questioning this practice, especially in healthy patients without difficult airways. Waiting to confirm the ability to mask ventilate prior to giving a muscle relaxant is an example of a practice in anesthesia that is probably not completely evidence-based.

 

I found this novel study to be particularly interesting and provided important, evidence-based results that are clinically significant. Results demonstrated, at least in healthy, non-obese patients with normal airways, that muscle relaxants do not worsen face mask ventilation. In fact, succinylcholine improved the ability to mask ventilate by mainly dilating the oral airway. As I reflect back on when I administer succinylcholine more times than not I have found it improves, rather than worsens, face mask ventilation. It is nice to see that my clinical experience is supported by evidence.

 

There are a few limitations of this study. These results cannot necessarily be generalized to patients who may be difficult to ventilate. Although I think in general succinylcholine does help improve face mask ventilation even in patients who may be considered difficult to mask ventilate. When deciding whether or not to confirm mask ventilation prior to administration of a muscle relaxant, anesthesia providers should consider the patient’s airway exam and history, the equipment and resources available in the event they get into a cannot ventilate, cannot intubate scenario, and their clinical experience. Also, the authors compared tidal volume results between the three time periods (control, interval, and paralysis) using paired t-tests. However, the more appropriate statistical test would have been a repeated measures analysis of variance. Therefore, they should have lowered the P value they considered significant (i.e., P <0.01).

 

Dennis Spence, PhD, CRNA

 

 

 

 

Additional Thoughts: I would probably be considered a more conservative anesthetist in most ways. I still believe strongly in the practice of verifying the ability to ventilate before administering a muscle relaxant. Here is why this study doesn’t change my mind. This is only one study. I’m not ready to change my practice in such a large way without considerable evidence. This study basically tells us that ventilation improved somewhat after muscle relaxants in patients who weren’t hard to ventilate in the first place. Relaxation may not improve ventilation in patients who are truly difficult or impossible to mask ventilate. And even if muscle relaxant improved ventilation in most patients who were difficult to ventilate prior to giving a relaxant, that still leaves some patients who don’t get easier to ventilate. We must consider the safety of all, not just the majority. I don’t want to end up with a can’t ventilate, can’t intubate patient whom I’ve just paralyzed for a prolonged period; especially when it is so easy to try to give one breath first.

 

I agree with Dr. Spence that this study has things to teach us. And it may mean we can be a little more liberal in when we paralyze patients. I believe it is still valuable to take a moment for at least one breath before relaxation so we’ll have some information about the ease or difficulty of mask ventilation before we make the decision to paralyze.

 

Michael A. Fiedler, PhD, CRNA

 

 

(Abstract contributing editor)

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 2012 Anesthesia Abstracts · Volume 6 Number 10, October 31, 2012




Equipment & Technology
Stroke volume variation as a guide to fluid administration in morbidly obese patients undergoing laparoscopic bariatric surgery

Obes Surg 2010;20:709-715

Jain A, Dutta A


Abstract

Purpose The purpose of the study was to evaluate the adequacy of stroke volume variation monitoring to guide intra-operative fluid management in bariatric surgery patients.

Background Determining the appropriate amount of intravenous fluid to administer to the bariatric surgery patient can be extremely difficult. This difficulty is the result of not knowing exactly how much fluid these higher acuity patients can tolerate as they suffer from numerous cardiovascular and other physiologic derangements related to their obesity. Adverse physiologic responses to both restrictive and liberal fluid administration, which also occur in the non-obese, are often exaggerated in the obese. For example, restrictive fluid administration can cause end organ failure, while liberal fluid administration can cause a harmful positive fluid balance. There are very few, if any, evidence based guidelines available for use in directing intraoperative fluid therapy for the obese person undergoing bariatric surgery. Goal directed approaches are, however, gaining widespread popularity. Traditional physiologic measures, such as central venous pressure, fail to demonstrate the desired level of sensitivity and specificity. They are no longer considered a superior method to determine fluid status. Current research appears to be centered on more functional parameters, such as stroke volume variation (SVV), [see notes at end for description] as they are demonstrating a greater degree of sensitivity and specificity.

 

Methodology Fifty patients undergoing bariatric procedures, such as gastric bypass and sleeve gastrectomy, were enrolled in this prospective pilot study. All patients received a standardized general anesthetic. Intraoperative crystalloid administration was guided by the SVV measurement which was maintained at <10% by infusing 100 mL boluses of IV fluid. In addition to SVV, the following variables were measured: invasive and non invasive blood pressure, heart rate, central venous pressure, mean arterial pressure, cardiac output, stroke volume, systemic vascular resistance, urine output, arterial blood gas values, and electrolyte profiles. Outcomes of care were evaluated as they related to the management of intra- operative fluid administration guided by the SVV.

 

Result All 50 patients completed this evaluation study. Following were the key findings:

  • Using SVV < 10% as the goal, mean volume of intravenous crystalloid infused was 1,990 mL over more than a 3 hour surgery (mean surgery duration = 207 + 50 min)
  • A significant positive correlation was observed between the duration of surgery and the amount of crystalloid infused
  • No significant correlation was observed between BMI and fluid administered
  • Cardiac index and cardiac output were maintained higher than baseline values using SVV guided fluid management
  • Heart rate, blood pressure, and stroke volume were maintained at adequate levels
  • Central venous pressure and SVV did correlate, but only during the first 2 hours of anesthesia time; the correlation was inconsistent after the first 2 hours

 

There were no adverse events related to peri-operative fluid management guided by SVV. All patients were discharged home on post-operative day 3 or 4.

 

Conclusion In this observational study of the morbidly obese undergoing bariatric surgery with a standardized anesthetic, the use of stroke volume variation to guide fluid administration and management resulted in favorable patient outcomes.

 

Comment

This study had significant limitations (not a true experimental design, for example). Nevertheless, I did find it extremely valuable as it relates to my clinical practice. This research added a piece of evidence in an area in our practice that we desperately need it; the use of reliable and valid physiologic measurements to guide perioperative fluid administration in high acuity individuals. We all know that optimal preload conditions are beneficial. This is especially true in various subsets of the population we serve, such as the obese undergoing higher risk procedures. We also understand that one of the priority reasons we administer fluid challenges and/or boluses is to increase stroke volume. However, where we lack evidence relates to knowing what is the best way to determine where each patient is on the Frank-Starling curve, and therefore which patients will safely respond to fluid challenges by increasing cardiac output. Often times the left ventricle of the morbidly obese person does not have the ability to functionally respond to nonspecific or ill calculated fluid administration. We arbitrarily treat hemodynamic compromise with fluid and the result is development of pulmonary edema and heart failure. It is important to verify fluid responsiveness with a method that is reliable and valid. Much evidence is leading us to the use of stroke volume variation for this purpose. Because the morbidly obese typically have associated cardiovascular derangements, they are considered at greater risk for ‘falling off’ the Starling curve. We have few evidence based guidelines regarding intraoperative fluid administration for lower acuity patients and even less information to guide fluid management for the morbidly obese with numerous comorbidities. Understanding stroke volume variation and using it as a guide to safely manage fluid administration may prevent the adverse effects of both hypo- and hypervolemia, and the poor outcomes we observe in way too many clinical scenarios.

Mary A Golinski, PhD, CRNA


Explanation of stroke volume variation (SVV) - SVV is the variation in stroke volume associated with the respiratory cycle. It is seen on an arterial waveform as the up and down movement of the arterial waveform baseline during respiration. During spontaneous ventilation, arterial BP decreases during inspiration and increases during exhalation. During positive pressure ventilation, arterial BP increases during inspiration and decreases during exhalation. These fluctuations are related to changes in intrathoracic pressure. Less than 10% variation with respiration is normal. Greater than 10% variation indicates that stroke volume is falling significantly during respiration.

SVV is an indicator of relative preload and the heart’s responsiveness to an IV fluid bolus. SVV has greater sensitivity and specificity in predicting response to a fluid bolus compared to traditional hemodynamic indicators. New technology measures SVV in an arterial line waveform and calculates the percentage Stroke Volume Variations. The SVV value and associated waveform is displayed on a monitor screen. This same monitor uses arterial pressure, age, gender, and body surface area to calculate (not measure) stroke volume and cardiac output.


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 10, October 31, 2012




General
Intraoperative neuromuscular monitoring site and residual paralysis

Anesthesiology 2012;117:964-72

Thilen SR, Hansen BE, Ramaiah R, Kent CD, Treggiari MM, Bhananker SM


Abstract

 

Purpose The purpose of this study was too determine if monitoring facial muscles around the eye was associated with a greater degree of residual neuromuscular blockade in the post anesthesia care unit (PACU) than monitoring the adductor pollicis (ulnar nerve).

 

Background Residual neuromuscular blockade in the early postoperative period is associated with increased morbidity. Residual paralysis after neuromuscular blocking agents (NMBDs) is defined as a train-of-four (TOF) ratio of less than 90% at the adductor pollicis. The incidence of residual paralysis ranges from 38-64% when measured qualitatively with a nerve stimulator. Sometimes due to the surgical procedure, other sites such as the eye muscles (orbicularis oculi or corrugator supercilii muscles) are used to evaluate TOF and residual blockade. However, previous studies have found that the eye muscles recover faster than the adductor pollicis. Thus, it is possible that patients may still have residual blockade if the eye muscles are used to confirm the TOF and sustained tetanus response. Because of this issue, several guidelines recommend the adductor pollicis be used to confirm lack of residual neuromuscular blockade. The authors of this study tested the hypothesis that intraoperative monitoring of the eye muscles is associated with increased risk of residual neuromuscular blockade in the PACU when compared to the adductor pollicis.

 

Methodology This was a prospective, observational, cohort study conducted at two academic institutions in Seattle, WA. Inclusion criteria included adult ASA status I-IV patients who were free from underlying neuromuscular disorders and scheduled for elective surgery requiring NMBDs. There was no control of the type of anesthesia, location of TOF monitoring (eye muscles or adductor pollicis), reversal agent timing or use, or which NMBDs were administered. Intraoperatively, anesthesia providers used conventional, qualitative [emphasis added] nerve stimulators for TOF monitoring (Digistim II Nerve Stimulator). Within 5 minutes of arrival to the PACU quantitative [emphasis added] assessment of neuromuscular block was performed using an acceleromyography device (TOF-Watch SX). Residual paralysis was defined as a TOF ratio < 90% at the adductor pollicis [Editors Note: baseline calibration with the acceleromyography device prior to surgery could not be completed].

 

The primary outcome of this study was a comparison of the incidence of residual blockade in patients who had TOF monitoring at the eye muscles or adductor pollicis. Data collected included age, gender, body mass index (BMI), ASA status, type of surgery, TOF at time of reversal, dose of neostigmine, type of NMDBs used, total dose of NMDBs, and time interval between last dose of NMBDs and quantitative measurement. Multivariable logistic regression was used to analyze the results and control for covariates.

 

Result A total of 150 patients completed the study. Eye muscles were monitored in 99 patients and the adductor pollicis in 51 patients. No differences were found in age, ASA status, BMI, surgery duration, TOF count and fade response at time of reversal, total and last dose of NMDBs, or the time interval between reversal administration and extubation. Patients in the eye muscle group were more likely to have undergone abdominal or thoracic surgery (85% vs. 41%, P < 0.01). Rocuronium was the most common NMBD used (81%). Eighteen patients arrived to the PACU intubated. All were breathing spontaneously.

 

In both groups, more than 70% of patients had a TOF of 4 without fade reported prior to neostigmine administration. The most common doses of neostigmine were 3 mg (n = 48) or 4 mg (n = 24). The time from neostigmine administration to extubation was 16 ± 15 minutes in the eye muscle group and 17 ± 10 minutes in the adductor pollicis group (P = NS). The time from neostigmine dose to TOF ratio measurement in the PACU was approximately 32 ± 20 minutes in both groups (P = NS).

 

The incidence of residual neuromuscular blockade (TOF ratio < 90%) was significantly greater in the eye muscle group (P < 0.01; Figure 1). The mean TOF ratio was 86% in the eye muscle group (range 0-115%). The mean TOF ratio was 93% in the adductor pollicis group (range 40-116%). (Editors note: reason for ratio >100% was because TOF-Watch device was not calibrated as required prior to administration of NMBDs). Patients who were in the eye muscle group were 5.5 times more likely to experience residual blockade in the PACU (P < 0.05). For every 10 minute increase in time from last NMBD administration until quantitative evaluation of the TOF in the PACU there was a 10% decrease in the odds of residual blockade (P = 0.03).

 

 

Figure 1. TOF Ratio

Figure 1

 

Compared to normal weight patients, overweight (BMI between 25-29.9 kg/m2) and obese patients (BMI > 30 kg/m2) were almost 4 times more likely to experience residual neuromuscular blockade (P = 0.01). No serious complications occurred. Two patients in the eye muscle group had TOF ratios of 0 in the PACU. Neither of these patients required intervention beyond close monitoring.

 

Conclusion Residual neuromuscular blockade was 5.5 times more likely to occur in patients who had their TOF monitoring at the eye muscles. The authors recommended clinicians consider using quantitative monitors (acceleromyography) or qualitative assessment of the TOF at the adductor pollicis to confirm complete reversal when possible prior to extubation.

 

Comment

Over the last few years there has been increased emphasis on recognition of the problem of residual neuromuscular blockade in the PACU.1,2 Residual paralysis places patients at increased risk for airway obstruction in the early postoperative period, especially in those with obesity and obstructive sleep apnea. In this study, over 50% of patients in the eye muscles group had residual paralysis (TOF ratio < 90%) as compared to only 22% in the adductor pollicis group in the PACU. This is an important finding because it provides evidence demonstrating using the TOF response at the eye muscles is not a reliable method for confirming full reversal of neuromuscular blockade.

 

So how should we apply these results to practice? First, I would monitor the adductor pollicis when possible intraoperatively and prior to giving reversal agent. Second, confirm the patient with sustained tetanus at the adductor pollicis prior to extubation. If you have the capability to quantitatively monitor the TOF ratio, do so. Newer monitors are starting to incorporate this technology. This is the most accurate way to evaluate for residual paralysis. The important thing to remember is that you need to calibrate the monitor after induction but before administration of the intubating dose of neuromuscular blocker. When the acceleromyography monitor is used without calibration, there is a tendency to overestimate the TOF ratio, which could lead to an underestimate of the true degree of residual blockade.

Dennis Spence, PhD, CRNA


1. Sauer M, Stahn A, Soltesz S, Noeldge-Schomburg G, Mencke T. The influence of residual neuromuscular block on the incidence of critical respiratory events. A randomised, prospective, placebo-controlled trial. Eur J Anaesthesiol. Dec 2011;28:842-848.

2. Brull SJ, Murphy GS. Residual neuromuscular block: lessons unlearned. Part II: methods to reduce the risk of residual weakness. Anesth Analg. Jul 2010;111:129-140.


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 2012 Anesthesia Abstracts · Volume 6 Number 10, October 31, 2012




Obstetric Anesthesia
Risk factors for failed conversion of labor epidural analgesia to cesarean delivery anesthesia: a systematic review and meta-analysis of observational studies

Int J Obstet Anesth 2012;21:294-309

Bauer ME, Kountanis JA, Tsen LC, Greenfield ML, Mhyre JM


Abstract

 

Purpose The purpose of this study was to identify risk factors associated with failed conversion of epidural analgesia to surgical anesthesia for cesarean delivery.

 

Background Conversion of epidural analgesia to a surgical block with a bolus of concentrated local anesthetic is the safest, and one of the most common anesthetic techniques used for cesarean delivery. Use of this technique minimizes the risks associated with general anesthesia, allows the mother to participate in the birth process, and avoids depressant effects of systemic anesthetics on the uterus and fetus. The Royal College of Anaesthetists have published guidelines specifying that the rate of general anesthesia for cesarean delivery in the parturient with an existing labor epidural should not be more than 3%. Therefore, it is essential that anesthesia providers understand what the risk factors are for failed conversion of epidural analgesia to surgical anesthesia. This would allow providers to develop strategies to minimize the need for general anesthesia for cesarean delivery.

 

Studies have identified seven common risk factors for failed epidural conversion:

  1. increased number of top-ups
  2. breakthrough pain during labor
  3. increased urgency for cesarean delivery
  4. higher body mass index or obesity
  5. increased duration of epidural analgesia
  6. lower cervical dilation at time of epidural placement
  7. use of an epidural versus combined spinal-epidural technique for labor analgesia. 

This study sought to examine these risk factors, using meta-analysis techniques, to determine which factors were associated with failed conversion of epidural analgesia to cesarean delivery surgical anesthesia.

 

Methodology The investigators conducted a systematic review and meta-analysis of observational studies published between 1979 and 2011. Retrospective and prospective studies; cohort, case-control, and cross-sectional studies were included. Articles that included failed conversion of epidural analgesia to surgical anesthesia for cesarean delivery as a primary or secondary outcome were included; however, the definition of failed conversion varied among studies. Definitions used included: undefined, requiring intravenous or inhalation supplementation, or conversion to general anesthesia. A standardized search strategy was chosen and investigators searched several databases (PubMed, EMBASE, and OvidSP) and hand searched the bibliographies for other articles for inclusion. The quality of the studies identified was evaluated using the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) checklist. Statistical analysis was appropriate.

 

Result The literature search identified 13 articles and included 8,628 parturients. Sample size of studies ranged from 94 to 1,830 parturients. Only 63% of the studies included information on all the STROBE checklist items. All studies were published between 1994 and 2009. The most common epidural anesthesia bolus regimen was 2% lidocaine with bicarbonate (1 mEq/10 mL) and epinephrine 1:200,000 (used in 7 studies). Studies compared or reported the use of several different local anesthetic solutions used for cesarean delivery includoing 3% 2-chloroprocaine, 2% & 1.5% lidocaine, bupivacaine, or levobupivacaine).

 

Overall, 5% of cesarean deliveries were performed with general anesthesia in patients who had an epidural for labor . In 7.7% of patients a second anesthetic, including spinal, repeat epidural, or general anesthesia, was required for the cesarean section. Eleven percent of patients required supplemental analgesia during cesarean delivery. Supplemental analgesia included: intravenous, inhalation, or an unspecified supplementation. There was high degree of heterogeneity in the rate of general anesthesia, repeat regional anesthesia, and supplementation; indicating a wide variation in results across the studies.

 

In four studies routine removal of the epidural catheter occurred without first attempting conversion to epidural anesthesia for cesarean delivery. The most common techniques reported for trying to manage inadequate epidural surgical anesthesia included:

  1. removing the epidural and placing a spinal (1 study reported this was done in 60% of inadequate epidurals)
  2. pulling the epidural catheter back 1 cm (1 study reported this was successful in 22 of 26 patients)
  3. epidural catheter replacement
  4. administration of general anesthesia without attempting a spinal
  5. conversion to general anesthesia due to prolonged or difficult surgery

 

In three of the studies the number of unscheduled boluses needed to maintain effective labor analgesia was measured. In these studies, patients who required 1 or more unscheduled boluses during labor had a 3-fold increase in failed conversion to surgical anesthesia (P < 0.05). In one study, investigators found parturients with failed epidural anesthesia had significantly higher pain scores 2 hours before cesarean delivery when compared to those without failed epidural anesthesia (P = 0.03).

 

In 7of the 13 studies, the urgency of need for cesarean delivery was evaluated. Parturients who required emergency cesarean delivery (i.e., immediate threat to life of woman or fetus) were 40 times more likely to receive general anesthesia if they had a failed epidural (P < 0.05). In 8% of these cases the epidural was not even bolused for cesarean delivery because epidural analgesia had been ineffective during labor. Two studies found a 4.6 times higher rate of conversion to general anesthesia if non-obstetrical anesthesia providers managed the anesthetic, a 7.6% vs. 1.6% failure rate (P < 0.05).

 

A longer duration of epidural analgesia, use of combined spinal-epidural analgesia, earlier epidural placement, and higher body mass index or obesity were not associated with higher epidural failure rates for cesarean delivery.

 

Conclusion In this systematic review, 5% of patients with a labor epidural required conversion to general anesthesia for cesarean delivery. An increased number of top-up boluses during labor, increased urgency of cesarean delivery, and anesthetic management by a non-obstetrical anesthesia provider were associated with failed conversion of epidural analgesia to surgical anesthesia for cesarean delivery.

 

Comment

Even though I do a lot of obstetric anesthesia I still get a little butterfly in my stomach when the surgeon says “I’m doing the allis test,” especially during a crash cesarean delivery. This is probably not a bad thing because it keeps me on my toes. I am sure many of our readers who do obstetrical anesthesia have experienced the same thing. One of the most vexing things about obstetric anesthesia is the fact that conversion of a labor epidural to a dense surgical block for cesarean delivery is not 100% in all patients. How you predict which epidurals may fail, and how you manage the patchy or failed epidural for cesarean delivery is what makes obstetric anesthesia one of the most exciting and challenging subspecialties in anesthesia.

 

I think the findings of this study are probably not surprising to most anesthesia providers. In my experience, patients who require multiple top-up boluses during labor many times are the ones I am taking back later for cesarean delivery. The need for a top-up is multifactorial; it could be the catheter was placed too deep initially and the patient has a one sided block so you pull it back 1 cm and re-bolus. Maybe the baby is malpositioned and the mother is experiencing back labor (i.e., occiput posterior). In this situation you may need to bolus a more concentrated solution. Maybe the patient had a “difficult back” and you had a tough time placing the epidural and after the initial bolus the patient had no appreciable block or pain relief. This is what makes obstetric anesthesia so challenging. It is also why experienced obstetric anesthesia providers may have lower epidural failure rates for cesarean delivery.

 

When I teach students I tell them the most important reason why we are placing an epidural, aside from pain relief, is so we can use it for cesarean delivery in an emergency. Sometimes that doesn’t work. As we saw in this study epidural failure rates are around 5%. The other advice I give them is, “when in doubt, pull it out.” This means if you are not confident that epidural catheter is going to work for cesarean delivery you should consider replacing it early when you have time. The worst situation in anesthesia is to be back in the operating room for a crash cesarean delivery with a 400 lb. morbidly obese parturient with a difficult airway and an epidural that does not work.

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 2012 Anesthesia Abstracts · Volume 6 Number 10, October 31, 2012




Pediatric Anesthesia
Comparison of 2 cuff inflation methods before insertion of laryngeal mask airway for safe use without cuff manometer in children

J Emerg Med. 2012 Nov 15 [Epub ahead of print]

Kim M, Bai S, Oh J, Youm S, Lee J


Abstract

Purpose The purpose of this study was to determine whether laryngeal mask airway (LMA) intra cuff pressures would be within a clinically acceptable range during insertion in pediatric patients using two different inflation techniques:  half the maximal recommended air volume or resting air volume. 

 

Background The LMA has gained widespread use for both anesthetists and pre-hospital providers. Learning to insert the LMA and establish and maintain an airway is relatively easy. Additionally, there are fewer complications as a result of LMA use compared to endotracheal intubation. Practitioners have acknowledged, and the literature supports, that the smaller LMAs used in the pediatric aged group are easier to insert when the cuff is partially inflated prior to insertion. What remains unknown is the safest volume of air used to inflate the cuff prior to insertion. There are more complications observed when cuff pressures are excessive, such as mucosal damage and airway edema, in children compared to adults. Additionally, the LMA is difficult to seat and air leakage occurs to a greater extent with abnormally high cuff pressures.

 

Most providers do not use manometers to measure intra cuff pressure, either before or after insertion of the LMA. It was hypothesized that both inflating the cuff prior to insertion with half the maximum recommended inflation volume for each size or inserting the LMA with a “resting volume” in the cuff (see methods) would result in a clinically acceptable final cuff pressure.

 

Methodology After IRB approval was obtained from guardians, 80 children scheduled for elective inguinal hernia repair under general anesthesia were randomized into one of two groups:  

 

  1. Half Volume Group: each LMA was fully deflated then filled with half the maximum inflation volume according to manufacturer’s guidelines.
  2. Resting Volume Group: each LMA was fully deflated then the pilot balloon valve was connected to a piston free syringe allowing the intra cuff pressure to equalize with atmospheric pressure. The syringe was then disconnected prior to insertion.

Normal saline was used to lubricate all LMAs and each size used was chosen according to the manufacturers guidelines. 

Inclusion criteria for the sample were:

  • ASA physical status I or II
  • Age 0-9 years
  • Weight between 5-30 kg

A standardized sevoflurane general anesthetic was administered for all cases without nitrous oxide or neuromuscular blocking agents. An experienced provider inserted all LMAs using a rotational technique. Successful insertion was confirmed using standard practice such as normal capnography waveforms and symmetrical chest wall excursion. Insertion time, ease of insertion, necessary manipulations of the LMA, and repositioning of head or neck were documented. Upon securing the LMA, the intra cuff pressures were measured using a manometer. Oropharyngeal sealing efficacy was determined by measuring airway leak pressures and leak volume (see notes). Intracuff pressures were then adjusted to below 60 cm H20, or if less than 40 cm H20 and with a notable leak, air was inserted to maintain adequate ventilation. Fentanyl was administered or a caudal block performed for perioperative analgesia. The LMAs were removed when each child was awake. Any complications were documented.

 

Result A total of 78 patients were able to complete the study; 39 in each group. There were no statistically significant differences between groups in terms of demographic data which included: gender, age, height and weight, ASA status, LMA size, total anesthesia and surgery time. Statistically significant differences were noted between groups in the following variables:

  • Half Volume Group required more manipulations to seat the LMA properly (p = .007)
  • Half Volume Group had a lower mean intracuff pressure (P = .005)
  • Half Volume Group had fewer patients with intracuff pressures >60 cm H20 (P = .04)
  • Leak volume and leak fraction were lower in the Resting Volume Group only during mechanical ventilation (P = 0.01)

There were no serious complications in either group and evidence of pharyngeal morbidity was absent during the recovery phase for both groups.

 

Conclusion This study demonstrated that inflating the LMA cuff prior to insertion using the Half Volume technique in pediatric patients resulted in a safe intracuff pressure. These pressures may minimize the risk of airway complications. It also demonstrated that using the Resting Volume technique was beneficial as it required less manipulation of the LMA during insertion and an appropriate seal was maintained during mechanical ventilation. Neither technique resulted in evidence of trauma to the airway.

 

Comment

After analyzing the results of this study very cautiously, I concluded the following. We should be inserting LMAs for all patients, irrespective of age, using a technique which the evidence supports as creating minimal risk of trauma or complications. We should maintain the LMA using techniques that do the same. The most logical manner to approach the process of inserting and maintaining an LMA is with:

  1. selection of size based on weight and age
  2. always approach insertion with a gentle hand
  3. consistently use a manometer!

A manometer is a very important tool in this clinical scenario, yet I rarely see it used. The manometer provides us with an additional piece of data; a measurement that we can use to prompt an intervention on our part in terms of inflating or deflating the LMA cuff. Using a manometer appears to be one of the best ways to decrease the risk of trauma to the airway when an LMA is properly inserted. Why is it not used on a consistent basis? This study demonstrated that using a Half Volume insertion method minimized excessive intracuff pressures; which are known to cause pharyngeal complications. However, I believe this is most true when the excessive pressures exist for any time beyond insertion time.

 

This study also demonstrated that a Resting Volume insertion technique resulted in the need for fewer manipulations to establish and maintain the airway quickly. This is perplexing: should we insert the LMA using the Half Volume technique that created adequate intra cuff pressures or the Resting Volume technique that allows for quick establishment of the airway with minimal manipulations required? My own conclusion is this: be extremely gentle, insert the LMA with a half volume technique, immediately assess the cuff pressure with a manometer, and adjust both position and pressure as necessary. If we are secure with the information that excessive intra cuff pressure in the LMA is known to create complications, we should be consistently measuring cuff pressures in order to minimize complications.

Mary A Golinski, PhD, CRNA


 

Notes: Oropharyngeal sealing efficacy was determined by measuring 1) the airway leak pressures and 2) the leakage/volume fractions.


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 10, October 31, 2012




Respiration & Ventilation
Society for ambulatory anesthesia consensus statement on preoperative selection of adult patients with obstructive sleep apnea scheduled for ambulatory surgery

Anesth Analg 2012;115:1060-8

Joshi GP, Ankichetty SP, Gan TJ, Chung F


Abstract

 

Purpose Obstructive sleep apnea (OSA) has emerged as a significant perioperative risk due to both its prevalence in the American population and its serious comorbidities. Coupled with the fact that a majority of operative and therefore anesthetic experiences occur in an outpatient setting, the Society for Ambulatory Anesthesia (SAMBA) charged a task force to develop clinical practice guidelines to assist in the selection of OSA patients appropriate for outpatient surgery.

 

Background Practice guidelines for the perioperative management of OSA patients were published in 2006. These guidelines were not based on randomized controlled trials or meta-analyses, but primarily upon expert opinion and consensus agreement among committee members. The committee recommended a scoring system for perianesthesia management based on OSA severity, the invasiveness of proposed surgery and anesthetic, and the need for postoperative opioid use. To date, the ASA scoring tool’s validity has not been established by even a single published study. Since that time, not only has an alternative screening questionnaire for OSA been developed and validated, but several studies have been published about OSA and the perioperative factors that influence patient outcomes.

 

Methodology A systematic review of the literature was done on adult OSA patients undergoing ambulatory surgery using the usual methods (Cochrane Central Register, MEDLINE, EMBASE). Two reviewers evaluated the identified studies for eligibility, focusing on randomized controlled trials, prospective observational trials, and retrospective trials that reported intraoperative events, postoperative complications, hospital admission and mortality in the target population. Strength of evidence was evaluated before inclusion in the review. Data extraction included associated comorbidities, method of OSA diagnosis, procedure, type of anesthesia, and any abnormal perioperative events whenever available. After review of these data, the task force used the Delphi method to formulate their recommendations.

 

Result From an initial search of 1,905 articles, only 7 fulfilled the complete search criteria; two prospective observational studies and five retrospective chart reviews. Interestingly, there seemed to be no correlation between events that are commonly used as surrogates for adverse outcomes; such as desaturation, need for oxygen, or atelectasis; and actual adverse outcomes such as the need a for surgical airway, anoxic brain injury, delayed discharge or unanticipated hospital admission, or death. The seven studies reviewed used different methods for identifying OSA patients and different definitions of complications. Within this limited framework, the task force developed the following recommendations, some of which are inconsistent with the 2006 ASA guidelines.

 

First, preoperative screening for OSA should be performed using the STOP-Bang screening questionnaire, not the older ASA checklist (table 1). If 3 or more answers to STOP–Bang questions are “yes” there is a high risk of moderate to severe OSA. STOP-Bang has been clinically validated as the screening tool with the highest sensitivity for identifying OSA patients in several studies. It is not only acceptable but recommended to treat a patient as if he/she has OSA on a presumptive basis when identified with this tool.

 

 

 

Table 1: STOP-BANG Questionnaire3

Do you snore loudly (louder than talking or loud enough to be heard through closed doors)?

Do you often feel tired, fatigued, or sleepy during daytime?

Has anyone observed you stop breathing during sleep?

Do you have or are you being treated for high blood pressure?

BMI > 35 kg/m2?

Age > 50 years?

Neck circumference > 40 cm?

Gender male?

NOTE: If 3 or more answers are “yes” there is a high risk of moderate to severe OSA. In the truncated version (use only the first 4 questions): if 2 or more answers are “yes” there is a high risk of OSA.

 

 

SAMBA’s report stressed the avoidance of opioids in OSA and recommends that ambulatory procedures should not be performed in OSA patients who cannot be managed with local, regional, or NSAIDs alone. That is, OSA patients who need opioids for painful procedures should be admitted and monitored appropriately.

 

OSA patients who use CPAP or BiPAP should use it postoperatively after discharge. If the patient is unable or unwilling to do so, careful consideration should be given to avoidance of ambulatory surgery. Patients and families should be educated about the disease and use of CPAP and the possibility of overnight hospitalization. Patients should be advised not to sleep in the supine position. In the special case of upper airway surgery, limited evidence was available and SAMBA declined to make specific recommendations.

 

Conclusion In the setting of either known or presumptive OSA combined with non-optimized comorbidities, the OSA patient is not recommended for ambulatory surgery. OSA patients with optimized comorbidities who are either able to use CPAP at home or whose pain will require only non-opioids may be acceptable for ambulatory surgery.

 

Comment

Obstructive Sleep Apnea is an old and well-described phenomenon. Comorbidities of OSA include hypertension, coronary events, stroke, and the risk of motor vehicle accidents. Most importantly, the OSA patient has an increased sensitivity to central nervous system depressants including neuraxial opioids. Guilleminault and Dement from Stanford University wrote a treatise on OSA in 19781 but obesity was not an epidemic 30 years ago and the general medical community paid little attention to OSA as a disease. As far back as 1991, the Stanford group found that self-reporting frequent snoring was a highly sensitive indicator of OSA.2 These and other reports were relatively ignored by the anesthesia community despite the fact that neurologists were publishing regularly about the adverse effects of sedatives and opioids in this population. It has taken several case reports of severe morbidity and mortality in postoperative OSA patients combined with a 32% obesity rate to get our attention. And it has taken even longer to develop a serious and educated approach to the anesthetic care of an OSA patient.

 

It is likely that retrospective and prospective reviews and case studies will continue to provide much perspective on OSA. In light of the well known risks of OSA, randomized controlled trials which rely on a control group for comparison are probably not possible or even ethical to conduct. Very large prospective studies would be a helpful addition to our knowledge base, particularly if the design included a 30-day follow-up looking for adverse events that may occur from residual anesthetic effects. In the meantime, it is clearly prudent to be very careful and conservative in our care of the OSA patient using not only published guidelines but common sense.

Penelope S Benedik, PhD, CRNA, RRT


1. Guilleminault, C. and Dement, W.C. (Eds.)  Sleep Apnea Syndromes. Alan R. Liss, Inc., New York, 1978 

2. Bliwise BL, Nekich JC & Dement WC. Relative validity of self-reported snoring as a symptom of sleep apnea in a sleep clinic population. Chest 1991;99:600-8.

3. Chung F, Yegneswaran B, Liao P, et al. STOP questionnaire: a tool to screen patients for obstructive sleep apnea. Anesthesiology 2008;108:812-21.


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 10, October 31, 2012