ISSN NUMBER: 1938-7172
Issue 3.12 VOLUME 3 | NUMBER 12

Editor:
Michael A. Fiedler, PhD, CRNA

Contributing Editors:
Penelope S. Benedik PhD, CRNA, RRT
Joseph F. Burkard, DNSc, CRNA
Mary A. Golinski, PhD, CRNA
Gerard T. Hogan, Jr., DNSc., CRNA
Alfred E. Lupien, PhD, CRNA
Dennis Spence, PhD, CRNA
Steven R. Wooden, MS, CRNA

Assistant Editor
Jessica Floyd, BS

A Publication of Lifelong Learning, LLC © Copyright 2009

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
RISK OF PULMONARY ASPIRATION WITH LARYNGEAL MASK AIRWAY AND TRACHEAL TUBE: ANALYSIS ON 65,712 PROCEDURES WITH POSITIVE PRESSURE VENTILATION
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  RANDOMIZED CONTROLLED TRIAL OF THE PENTAX AWS, GLIDESCOPE, AND MACINTOSH LARYNGOSCOPES IN PREDICTED DIFFICULT INTUBATION
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GENERAL
NASOGASTRIC TUBE INSERTION USING DIFFERENT TECHNIQUES IN ANESTHETIZED PATIENTS: A PROSPECTIVE, RANDOMIZED STUDY
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OBSTETRIC ANESTHESIA
THE EFFICACY AND SAFETY OF CONTINUOUS INTRAVENOUS ADMINISTRATION OF REMIFENTANIL FOR BIRTH PAIN RELIEF: AN OPEN STUDY OF 205 PARTURIENTS
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UP-DOWN DETERMINATION OF THE 90% EFFECTIVE DOSE OF PHENYLEPHRINE FOR THE TREATMENT OF SPINAL ANESTHESIA-INDUCED HYPOTENSION IN PARTURIENTS UNDERGOING CESAREAN DELIVERY
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  A RANDOMIZED COMPARISON OF LOW DOSES OF HYPERBARIC BUPIVACAINE IN COMBINED SPINAL-EPIDURAL ANESTHESIA FOR CESAREAN DELIVERY
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PATIENT SAFETY
LATERAL ANTEBRACHIAL CUTANEOUS NEUROPATHY AS A RESULT OF POSITIONING WHILE UNDER GENERAL ANESTHESIA
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REGIONAL ANESTHESIA
COMPARISON OF ROPIVACAINE 0.2% AND 0.25% WITH LIDOCAINE 0.5% FOR INTRAVENOUS REGIONAL ANESTHESIA
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Airway

Bernardini A, Natalini G


Risk of pulmonary aspiration with laryngeal mask airway and tracheal tube: analysis on 65,712 procedures with positive pressure ventilation

Anaesthesia 2009;64:1289-1294

Bernardini A, Natalini G

Abstract

Purpose            The purpose of this study was to test the hypothesis that pulmonary aspiration of gastric contents was more likely when the airway was managed with an LMA than an endotracheal tube when patients were mechanically ventilated.

Background            The Laryngeal Mask Airway (LMA) has a number of advantages over an endotracheal tube and it can be useful in the management of a difficult airway when ventilation through a facemask is difficult. Nevertheless, the LMA does not seal the trachea against entry of gastric contents as well as an endotracheal tube (ETT). Positive pressure ventilation may result in gastric inflation and increase the risk of regurgitation and aspiration during LMA use. There is, however, little evidence about the actual risk of pulmonary aspiration with an LMA vs. an ETT during mechanical ventilation. Criteria considered to contraindicate the use of an LMA are based primarily on opinion and not on evidence.

The overall incidence of pulmonary aspiration (all types of airway management) has been reported to be between 1 in 3,216 and 1 in 14,139 general anesthetics.

Methodology            This retrospective study examined data in a preexisting quality improvement database. Data had been collected over a 10+ year period. Records were included in the analysis if either an LMA or ETT was used during a general anesthetic with mechanical ventilation. The selection of an LMA for airway management was driven by locally accepted contraindications to LMA use including: patients who were not NPO, intestinal obstruction, pregnancy, procedures involving the airway, and prone position. An LMA was occasionally used when one or more of these contraindications were present in a difficult airway situation.

Default volume controlled ventilator settings were tidal volume 8 – 10 mL / kg with respiratory rate adjusted according to the end tidal CO2. Surgical procedures included major abdominal, urologic, gynecologic, retroperitoneal, and laparoscopic surgery. Pulmonary aspiration of gastric contents was defined as the presence of gastric contents or bilious fluid in tracheal aspirate; bilious fluid on the LMA or in the oropharynx; or postoperative dyspnea, hypoxia, or “auscultatory abnormalities.” When a case of aspiration was identified in the quality improvement database the original chart was reviewed to verify the data.

Result            Slightly over 1,000,000 cases were contained in the database. Of those, 65,712 met the criteria for inclusion; general anesthesia and mechanical ventilation with either an LMA or ETT. Of those, 2,517 were major abdominal surgery or laparoscopy performed with an LMA. The airway was managed with an LMA in 1.7% of cases in which a contraindication to LMA use was present.

Aspiration occurred in 10 cases. Of these, 4 occurred during an elective procedure; 2 with an LMA and 2 with an ETT. The other 6 occurred during a non-elective procedure; 1 with an LMA. Only 2 of these patients were admitted to intensive care due to aspiration related problems; 1 of the ICU admissions was an LMA patient and 1 was an ETT patient. The occurrence of pulmonary aspiration in patients whose airway was managed with an LMA and mechanical ventilation was no different than those whose airway was managed with an ETT (odds ratio 95% confidence interval 0.09-1.4; P=0.141). The power of the study (the probability of rejecting the hypothesis when it is false) was calculated after the fact to be 0.69.

The primary factor associated with pulmonary aspiration was emergency surgery, not the airway management device. The overall incidence of aspiration was 1 in 6,571 anesthetics.

Conclusion            The incidence of pulmonary aspiration was no greater when an LMA was used than when an ETT was used during general anesthesia with mechanical ventilation. Institutional contraindications to LMA use may have influenced the results.

 

Comment

The focus of this study was the risk of aspiration when mechanical ventilation was used with an LMA. Accepted contraindications to LMA use were observed. The study was not about the risk of using an LMA for any and every case. It was about the added risk (if there is any) of using mechanical ventilation with an LMA. I’m glad to see this question addressed. Many of my colleagues are hesitant to use a ventilator with an LMA, yet manually bagging with an LMA is fine. Both are positive pressure ventilation. If our concern is insufflating the stomach with air it can happen with either method of ventilation. In my view, it is all about technique. I sometimes use mechanical ventilation with an LMA but I don’t use the ventilator the same way I’d use it with an ETT. I take care, for example, to keep peak pressures below 20 cm H2O. This study indicated that there may not be any increased risk of aspiration when mechanical ventilation is used with an LMA (see limitations in the following paragraphs). While I’m not ready to use an LMA as widely as this group apparently did, I do believe that with proper technique mechanical ventilation can safely be used with an LMA.

While the study is retrospective, it is unlikely it could have been conducted any other way, and, as such, it is probably nearly the best we are going to get. As retrospective studies go, this was a good one. Most retrospective studies are not based upon a detailed quality improvement database. The authors also took the wise step of reviewing the charts of all patients identified by the QI database as having experienced pulmonary aspiration. And, it has the advantage of including a large number of patients, especially important for a relatively low frequency event such as aspiration. Still, few aspirations were detected and there may have been a true difference in the aspiration rate that was undetectable as a result. Based upon the detailed statistical tests they reported and, in my judgment, one error in analysis, I believe there is a reasonable chance that the actual incidence of pulmonary aspiration may have been greater with the LMA than with an ETT (see note following).

The investigators rightly point out that the QI database may not have detected all cases of aspiration because complications were reported to the database by the anesthesiologist caring for the patient. Self reporting tends to underestimate the incidence of a complication because the clinician unconsciously gives themself the benefit of the doubt and because reporting can get put off until later and forgotten.

While it has a couple limitations, this study is important and enlightening because it is generally well done and encompasses a very large group of patients. The institution where this study was conducted does a great service by taking the time and effort to maintain a detailed quality improvement (QI) database for over a decade. Without it, this study would not have been possible.

Michael Fiedler, PhD, CRNA

NOTE: The upper boundary of the adjusted odds ratio 95% CI of the risk of aspiration with an LMA was 5.62 times greater than an ETT. A one sided test was used to calculate the power of the study.

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 12, December 31, 2009





Malik MA, Subramaniam R, Maharaj CH, Harte BH, Laffey JG


Randomized controlled trial of the pentax AWS, glidescope, and macintosh laryngoscopes in predicted difficult intubation

Br J Anaesth 2009;103:761-768

Malik MA, Subramaniam R, Maharaj CH, Harte BH, Laffey JG

Abstract

Purpose            The purpose of this study was to assess the efficacy of direct laryngoscopy with a Macintosh blade, the Pentax AWS, and the Glidescope in patients with risk factors for difficult intubation and patients with a history of difficult intubation.

Background            Failed intubation is an important cause of morbidity and mortality. Difficult intubations can result in airway trauma even when successful. Indirect laryngoscopes are useful because, unlike a direct laryngoscope, they do not require alignment of the oral, pharyngeal, and tracheal axes.

The Pentax Airway Scope (AWS) and the Glidescope have both been shown to facilitate endotracheal tube (ETT) placement in normal, simulated difficult, and clinically difficult airways.

Methodology            This prospective study included ASA physical status I-III patients, 16 years old and older, with risk factors for difficult intubation, who required general anesthesia and endotracheal intubation. To be considered “at risk” for difficult intubation, patients either had a history of difficult intubation or their preanesthetic assessment included at least two of the following three findings:

·      thyromental distance < 6 cm

·      Mallampatti class ≥ III

·      inter-incisor distance < 4 cm.

Patients with risk factors for aspiration of gastric contents were excluded. Equal numbers of patients were randomized into a Macintosh direct laryngoscopy group (#3 blade in females, #4 blade in males), a Pentax AWS group, and a Glidescope group. The Glidescope “Cobalt” model with a disposable blade was used. Men received an 8.5 mm ETT and women a 7.5 mm ETT. Failed intubation was defined as an intubation attempt that took longer than 60 seconds or which did not result in the ETT being placed in the trachea. The Intubation Difficulty Scale (IDS) was used to score the level of difficulty of each intubation attempt. The IDS is an instrument that assigns a numeric score to seven different aspects of the intubation process. An IDS of “0” is an easy intubation. A score of “4” is associated with a moderately difficult intubation. While strictly speaking the IDS score has no maximum, “15” would be a very involved and difficult intubation.

A standard anesthetic induction and maintenance was used for all patients. Induction included fentanyl 1 - 1.5 µg/kg, propofol 2 - 4 mg/kg, sevoflurane 2 - 2.5% in oxygen, and atracurium 0.5 mg/kg. After intubation, sevoflurane was reduced to 1.25 - 1.75% and 66% nitrous oxide was added. All intubations were performed by one of three anesthetists. Each had performed at least 500 intubations with the Macintosh laryngoscope and 50 patient intubations each with the Pentax AWS and the Glidescope.

Result            A total of 75 subjects were included in the study. Demographic characteristics, airway assessments, and dose of anesthetic drugs administered were similar between groups.

Intubation Difficulty Scale (IDS) scores were higher in the Macintosh group than in the Pentax AWS or Glidescope groups. IDS scores were about the same in the Pentax AWS and Glidescope groups.

At least moderately difficult intubations occurred in 14 (56%) Macintosh patients, no Pentax AWS patients, and 1 (4%) Glidescope patient. Intubation was unsuccessful in 4 (16%) Macintosh patients, no Pentax AWS patients, and 1 (4%) Glidescope patient.

There was no difference between groups in the duration or number of intubation attempts or the incidence of complications.

Following intubation, heart rate and mean arterial pressure increased statistically significantly, but not clinically significantly, in the Macintosh and Glidescope groups but not in the Pentax AWS group.

Conclusion            In patients with risk factors for difficult intubation, the ease and success rate of intubation with the Pentax AWS and Glidescope were better than intubation with the Macintosh laryngoscope. While not clinically significant, HR and BP increased less in the Pentax AWS group than in the Macintosh or Glidescope groups.

 

Comment

I was encouraged when I saw this study because it examined the utility of the Pentax AWS and Glidescope in real patients who had risk factors for difficult intubation. Previous studies I’ve read have either been done in patients with normal airways or with a difficult airway simulator. Ultimately I was let down because the investigators put most of their efforts into the Intubation Difficulty Scale (IDS) and analyzed the IDS data incorrectly, greatly limiting what the IDS scores can teach us.

There are some things we can learn from this study, though they lack the certainty of statistical significance. Both the Pentax AWS and the Glidescope Cobalt resulted in easier intubations than the Macintosh laryngoscope in real patients at risk for difficult intubation. And, all but one of the intubations with the Pentax AWS and Glidescope were successful while 4 of 25 (16%) in the Macintosh group were not. We probably would have guessed this outcome, but it is still nice to see our clinical experience confirmed under research conditions.

The investigators chose the number of patients in their study primarily to compare the IDS data, which they mistakenly viewed as if the IDS measured like a ruler (equal “distance” between each number and 4 is twice as much as 2). When an instrument produces an overall score from the number of anesthetists involved in the intubation, the number of intubation attempts, and whether the laryngoscopist lifted the laryngoscope blade harder than normal the resulting score is simply an order of increasing difficulty. An IDS score of 6 doesn’t mean the intubation was twice as hard as an IDS score of 3. It may only mean that two other people came in the room to help with the intubation and one of them pushed on the neck. Of course, everyone with risk factors for a difficult intubation don’t end up being a difficult intubation. If the investigators had included more patients and stuck to things they could really measure accurately, like number of successful intubations and time required for intubation, this study would have been much more helpful.

 

Michael Fiedler, PhD, CRNA

The IDS score is described in the following article: Anesthesiology 1997;87:1290

 

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 12, December 31, 2009




General

Appukutty J, Shroff PP


 

Nasogastric tube insertion using different techniques in anesthetized patients: a prospective, randomized study

Anesth Analg 2009;109:832-835

Appukutty J, Shroff PP

 

Abstract

Purpose            The purpose of this study was to compare four techniques of nasogastric tube (NG) insertion on the basis of number of attempts needed, success rate, time for insertion, and complications.

Background            The failure rate for NG tube insertion in an anesthetized, intubated patient is about 50%. On subsequent attempts, the NG can become more difficult to place as it becomes warm and more flexible, resulting in kinking and coiling. NG tube stiffness and patient head and neck position are key factors in successful insertion.

Methodology            This prospective, randomized study included 200 patients between 20 years and 70 years old who were undergoing general anesthesia and needed an NG tube placed. The nostril through which the NG would be passed was selected based upon its relative size and the volume of air flow during exhalation. A 14 French NG tube was used in all patients. A maximum of two insertion attempts were allowed. Patients were randomized into four groups.

Control patients had a lubricated NG tube inserted while the head was in a neutral position.

Guidewire patients had a ureteral guidewire inserted into the lumen of the NG tube to increase its stiffness. In other respects the NG tube was inserted in the same manner as control patients.

Slit ETT patients first had the NG tube advanced through the nose and out the mouth. A standard 7 mm endotracheal tube (ETT) was prepared by slicing it longitudinally so the NG tube could be passed through it and then the ETT removed from the middle of the NG tube. The NG tube was then passed through the cut ETT until the tip of the NG was even with the tip of the ETT. Next, the well lubricated, modified ETT was advanced blindly into the oropharynx to a depth of 18 cm. The NG was advanced further through the ETT. The ETT was then pealed off from the NG tube and withdrawn from the oropharynx simultaneously. Finally, the NG was pulled back through the nose until the desired length remained in the stomach.

Neck Flexion patients had a lubricated NG tube inserted to a depth of 10 cm. Then, the patient’s neck was flexed and pressure applied to the side of the neck while the NG tube was advanced in the same manner as control patients.

Result            Data were collected on 200 patients. There were no statistically significant differences in demographic data between groups.

In the Control group, the NG tube was successfully inserted 72% of the time. In the Guidewire and Slit ETT groups NG tube insertion was successful 92% of the time. The Neck Flexion success rate was 94%.

 

First Attempt Success

Group

% Success

P value (compared to control)

Control

34%

 

Guidewire

66%

0.002

Slit ETT

82%

<0.001

Neck Flexion

82%

<0.001

 

Insertion Time

Group

Seconds

P value (compared to control)

Control

56 ± 36

 

Guidewire

42 ± 29

NS

Slit ETT

98 ± 43

<0.05

Neck Flexion

31 ± 19

<0.05

 

Kinking occurred in 20% of Control patients and 8% each of Guidewire and Neck Flexion patients. Bleeding was most common in Slit ETT patients at 22%. No other group experienced bleeding. Overall, most complications were related to kinking of the NG tube.

Conclusion            Neck flexion and lateral neck pressure resulted in the highest rate of successful NG insertion, the fastest rate of insertion, the fewest complications, and required no additional equipment.

 

Comment

Anyone who has worked in the same room every day, doing the same kind of case, and inserting an orogastric or NG tube required for the procedure in every one of them has probably known frustration. It can easily turn into either a long drawn out affair that delays incision or mucosal trauma that leaves the patient with a very sore throat postoperatively. I have. This simple, yet well conceived study suggests a method of NG insertion that may reduce my frustration level.

I do wish the authors had elaborated a bit more on how they performed the lateral pressure. It seems a little counterintuitive. Exactly where is the pressure applied? In what direction? On the same or opposite side as the NG tube is being inserted; or does it matter? I’m guessing that the “lateral neck pressure” must be important because I routinely use neck flexion without lateral pressure and I don’t think I have an 82% first try success rate.

Improving the speed and success of NG insertion during general anesthesia will not only make the day go more smoothly but should improve the comfort of our patients as well.

 

Michael Fiedler, PhD, CRNA

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 12, December 31, 2009




Obstetric Anesthesia

D?Onofrio P, Novelli AMM, Mecacci F, Scarselli G


 

 

The efficacy and safety of continuous intravenous administration of remifentanil for birth pain relief: an open study of 205 parturients

Anesth Analg 2009;109:1922-24

D’Onofrio P, Novelli AMM, Mecacci F, Scarselli G

 

 

Abstract

Purpose            This was a prospective, descriptive study examining the analgesic effects, patient satisfaction and safety of a continuous infusion of remifentanil used for labor analgesia.

Background            Remifentanil is an opioid with a strong affinity for mu-receptors; it is characterized by a short onset (60-90 s) and context-sensitive half-life (3-5 min). Currently it is not approved for the treatment of labor pain, though its use has been described in multiple reports.

Methodology            After obtaining informed consent, subjects requesting systemic analgesia for labor analgesia were enrolled at 32 weeks gestation. Neuraxial labor analgesia was not available at the investigators birthing center. After admission for labor, a continuous infusion of remifentanil (25 mcg/ml) was initiated at 0.025 mcg/ml/min, and increased after 3 minutes to 0.05 mcg/ml/min. The infusion was titrated to achieve a visual analogue pain score (VAPS) of ≤ 4 during contractions. The rate was increased by 0.006 mcg/kg/min to achieve a pain score ≤ 4 or a maximum rate of 0.15 mcg/kg/min. The rate was decreased to the previous rate if there was a 20% drop in heart rate or blood pressure, SpO2 ≤90%, decreased fetal heart rate variability (absence of variability or < 5 bpm), or an Observers Assessment of Alertness/Sedation (OAA/S) score >3. Supplemental oxygen was not administered. VAPS were obtained at 5 and 30 minutes after initiation of analgesia and with every complaint of pain. Side effects, Apgar scores, umbilical artery pH, need for neonatal naloxone, and patient satisfaction (4 point likert scale) were measured.

Result            A total of 205 women (mean age 33.6 ± 5.4 yrs; 72 ± 10 kg; 43% nulliparous; 82% spontaneous labor) received remifentanil during labor. Infusions were initiated on average at 4 cm (range, 2-10 cm) and infused for a median 140 min (range, 30-1010 min). Maximum infusion rates were < 0.050 mcg/kg/min in 21.4%, between 0.075-0.10 mcg/kg/min in 63.5%, and between 0.125-0.150 mcg/kg/min in 15.1% of subjects.

Three patients complained of nausea, and blood pressure and heart rate were maintained within 20% of baseline in all subjects. All subjects maintained SpO2 >95% (mean 98% ± 1%). Supplemental oxygen was not required for any subject. Eight subjects (4%) had OAA/S grade 2-3 (2 = drowsy with ptosis of eyelids, 3 = asleep but awakens with verbal stimulation); none had OAA/S >3. No fetal heart rate changes were noted and median Apgar scores at 1 and 5 min were 9 (range, 5-10) and 9 (range, 8-10). Mean umbilical artery pH was 7.3 ± 0.1. Five infants had pH <7.1 (three with anhydramnios and two with fetal macrosomia). These infants had the lowest Apgar scores. No neonate required naloxone. Most patients (88%) were satisfied with their analgesia.

Conclusion            This observational study demonstrated that a continuous infusion of remifentanil titrated to a VAPS ≤4 was a safe option for labor analgesia with minimal side effects.

 

Comment

Neuraxial techniques, epidural and combined spinal epidural (CSE), have become the primary mode of labor analgesia in recent years. Occasionally the anesthesia provider is faced with a parturient in labor that is unable or cannot receive an epidural of CSE for vaginal delivery (i.e, severe gestational thrombocytopenia, history of Harrington Rods). Remifentanil with its ultra-short onset, duration and lack of active metabolites is a suitable alternative. The investigators in this study provided additional evidence supporting the efficacy and safety of a continuous infusion (non-patient controlled analgesia (PCA)) in labor parturients who had one on one nursing care and anesthesia providers available to titrate the infusion to the parturient’s need.

The most important take home message I got from this study was that a continuous infusion of remifentanil titrated by an anesthesia provider to keep pain scores <4 is very labor intensive. As one can see from the results, a majority of the subjects (>78%) needed their infusions titrated up from the initial setting of 0.05 mcg/kg/min.  This was probably not a problem in the investigators facility which did not have a neuraxial analgesia service. However, it would be much more challenging to use the remifentanil protocol in this study on a busy labor deck with a high epidural rate.

Remifentanil PCA or continuous infusions require one on one nursing care and continuous pulse oximetry monitoring capabilities. Several protocols have been published which providers can use to administer remifentanil with or without a background infusion. The optimal dosing regimen depends on the needs of the patient and change with the progress of labor. Despite these challenges, I believe it is an additional “tool” anesthesia providers should keep in their tool box when faced with a parturient that cannot get an epidural. Anesthesia providers should consider having guidelines and policies in place to ensure the safe administration of remifentanil to laboring parturients.

 

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, Department of Defense or the United States Government.

 

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 12, December 31, 2009





George RB, Mckeen D, Columb MO, Habib AS


 

Up-down determination of the 90% effective dose of phenylephrine for the treatment of spinal anesthesia-induced hypotension in parturients undergoing cesarean delivery

Anesth Analg 2010;110:154-158

George RB, Mckeen D, Columb MO, Habib AS

Abstract

Purpose            The purpose of this study was to tentatively identify the Effective Dose 90% (ED90) of bolus phenylephrine for the treatment of maternal hypotension during cesarean section under spinal anesthesia.

Background            Hypotension is common in the course of spinal anesthesia for cesarean section. The incidence of hypotension has been reported to be as high as 80%. Fetal outcomes are better, and maternal nausea and vomiting is less common, when maternal hypotension is prevented or promptly treated. Ephedrine or phenylephrine are usually needed whether or not aggressive intravenous (IV) volume preloading was administered. Phenylephrine’s peak effect occurs within 45 seconds following IV administration. It produces preferential splanchnic vasoconstriction with some sparing of uterine artery constriction in pregnant women. The optimal dose of phenylephrine in this setting is, however, unknown.

Methodology            This prospective, double-blind, up-down dose finding study included healthy, nonlaboring, term pregnant adults. All women had their baseline blood pressure (BP) determined by the average of three readings taken two minutes apart while lying supine with left uterine displacement. Hypotension was defined as a decrease in systolic BP of 20% or more or an absolute systolic BP less than 90 torr. All women received an IV preload of 15-20 mL/kg of lactated Ringers solution beginning before block administration. The block was performed with women in the sitting position, between L-3 and L-5, with 12 mg hyperbaric bupivacaine, 15 µg fentanyl, and 100 µg morphine. After injection, women were positioned supine with left uterine displacement. BP was taken every minute for 10 minutes, then every 2.5 minutes. If phenylephrine was administered the BP was again taken every 1 minute.

After the block, if maternal BP met the criteria for hypotension, a study dose of phenylephrine was administered. Study syringes were prepared by a clinician uninvolved with the case. The initial dose of phenylephrine was 100 µg. Women only received a study dose of phenylephrine following their first episode of hypotension. For each subsequent study dose administered, the dose of phenylephrine in the syringe was increased or decreased by 20 µg according to the following procedure. If the previous dose failed to increase BP to within 20% of baseline (or >90 torr absolute) the dose of phenylephrine in the next study syringe was increased by 20 µg. If the previous dose restored maternal BP the next dose was randomized to be reduced by 20 µg with a 1 in 10 chance of a dosage reduction. Thus, if the BP did not increase the next dose was always greater. If it did, the next dose had a 90% chance of being the same and only a 10% chance of being smaller.

Result            A total of 65 subjects completed the study. Of those, 69% (45 subjects) experienced hypotension and were given a study dose of phenylephrine. There was no significant difference in the demographic characteristics, block height, or blood loss of women who became hypotensive and those who did not.

In hypotensive women, the mean decrease in systolic BP from baseline was 25% ± 7%, the median block height was T-4, and the mean blood loss was 481 mL ± 183 mL. The mean time from injection of the local anesthetic until the onset of hypotension was 5.8 min ± 3.6 min. Phenylephrine doses administered ranged from 80 µg to 180 µg. The study dose of phenylephrine failed to restore BP in at least one patient at all but the 180 µg dose. No hypertension (BP increase >20% above baseline) occurred at any dose. The ED90 of phenylephrine to restore BP was 147 µg (95% CI 98-222 µg).

Conclusion            These preliminary results suggested that the dose of phenylephrine needed to treat maternal hypotension is higher than previously believed. The ED90 of phenylephrine for treating maternal hypotension during spinal anesthesia for cesarean section was approximately 150 µg. The dose commonly administered, 100 µg, is at the extreme low end of the 95% confidence interval for this study.

 

Comment

The incidence of hypotension during spinal or epidural anesthesia for cesarean section appears to be about the same now as it was 25 years ago; early in my anesthesia career. Countless studies have searched for the volume of IV preload that would prevent maternal hypotension, without success. Trying to solve the problem by adding volume to the vascular system assumes that the cause of hypotension is on the venous capacitance side of the system. The assumption – venous pooling, less venous return to the heart, lower cardiac output, and, thus, lower BP. The fact that aggressively adding volume doesn’t prevent hypotension is a good indication that this assumption is incorrect or at least inadequate.

This study looked at maternal hypotension from the systemic vascular resistance (SVR) side of the vascular system and administered phenylephrine to increase SVR. It worked, restoring BP at a dose of about 150 µg. That should tell us something. It strongly suggests that the cause of maternal hypotension during spinal anesthesia lies on the SVR side of the vascular system rather than the venous capacitance side.

There is one important limitation and problem with this study that must be addressed. We have reason to believe that at some dose of phenylephrine uterine artery constriction will occur. Uterine artery constriction reduces placental perfusion and decreases fetal oxygenation. Given that this was a dose finding study, I’m surprised that there were no fetal assessments of any kind. They may not have been included because only one dose of phenylephrine was given. But in clinical practice I’m probably going to need more than one dose before the cord is clamped. I may even like to use an infusion. If we are going to apply this clinically we will need to know if it can cause fetal hypoxia.

For those who may read the full text of this article, I call your attention to the following statement in the discussion section: “… doses of phenylephrine in this range are unlikely to have any negative impact on neonatal … outcomes.” I was shocked to read this because there were NO fetal assessments in the study upon which to base it and the study was not designed to investigate the fetal or neonatal effects of maternally administered IV phenylephrine. This statement is without support in the study. I would hate for anyone to base their clinical practice on this unsupported statement. It significantly detracts from an otherwise well done and helpful study.

 

Michael Fiedler, PhD, CRNA

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 12, December 31, 2009





Leo S, Leong Sng B, Lim Y, Sia AT


 

A randomized comparison of low doses of hyperbaric bupivacaine in combined spinal-epidural anesthesia for cesarean delivery

Anesth Analg 2009;109:1600-1605

Leo S, Leong Sng B, Lim Y, Sia AT

 

Abstract

Purpose            The purpose of this study was to determine the characteristics of intrathecal administration of 7, 8, and 9 mg of bupivacaine administered via combined spinal-epidural in a group of parturients who presented for cesarean delivery. Specific variables of interest were block height, incidence of hypotension and need for epidural supplementation.

Background            Spinal anesthesia is commonly performed for the elective cesarean delivery due to the rapid onset and dense motor block. Combined spinal-epidural offers the advantage of having an opportunity to extend the block if it becomes necessary. Previous research has suggested that a combined spinal-epidural produces an increased block height compared to a single spinal administration. However, it is still unclear whether this difference in block height is significant enough to warrant adjustment of the dosage. This investigation was performed to determine if the three different dosages of bupivacaine (7, 8, and 9 mg) would result in different characteristics of the block, or a difference in side effects, when administered as a combined spinal-epidural technique.

Methodology            This approved study was conducted at a womens’ hospital in Singapore. Sixty parturients who were ASA I or II, singleton, and at full-term pregnancy were consented for the study. Exclusion criteria included women who were in labor, planned post-partum tubal ligation, allergy, or contraindication to the study medications, complication of pregnancy including: preeclampsia, multiple gestation, placenta previa. Patients with extremes of height and weight were also excluded (BMI <20 or > 35 kg/m2, height < 145 or >180 cm). Eighteen gauge peripheral IVs were started. Baseline HR and non-invasive blood pressure measurements were taken. All of the combined spinal-epidurals were placed by the two investigators who each had > 5 years experience with the technique. The subjects were randomly assigned to groups who would receive either 7, 8, or 9 mg of bupivacaine. The bupivacaine was 0.5% with 8% dextrose, and the resulting volumes administered were 1.4 mL, 1.6 mL, and 1.8 mL respectively. All subjects also received 100 mcg of intrathecal morphine. At the time of intrathecal injection, all subjects received 15 mL/kg of hydroxyethyl starch by intravenous infusion over 10-15 minutes. The CSE technique was performed with all subjects in the lateral decubitus position. The L3-4 interspace was used. The Tuohy needle was an 18 gauge and the Whitacre needle was a 27 gauge. After injection of the intrathecal dosage over 10-15 seconds, an epidural catheter was threaded 4 cm, and no medication was administered in the epidural unless it was deemed necessary (level < T6 or VAS > 40 mm).

A blinded investigator performed the assessment of the block height and hemodynamics at 2.5 min intervals for 30 minutes and at 5 min intervals after 30 minutes. The level of sensory block was determined using ice. Specific measurements included block height, time to maximal block height, blood pressure, heart rate, motor block (Bromage scale) and time to maximal Bromage score. Other data that was recorded was Apgar scores (1 and 5 min), duration of surgery, incidence of hypotension (defined as systolic < 90 mm Hg or decreased > 20% of baseline). Side effects such as nausea, vomiting, shivering, and the need for vasopressors were noted. Patients received either 100 mcg phenylephrine or 5 mg ephedrine as necessary. Any difficulty placing the CSE or unintentional dural puncture was also recorded.

Subjects were monitored in the PACU every 5 minutes. Discharge criteria for the PACU included a T-10 level, and a Bromage score of 2. A blinded observer also evaluated the subject at 24 hours post delivery to assess for common adverse effects such as post-dural puncture headache, nausea and/or vomiting, neurologic deficits, urinary retention, or backache.

Result            There were 20 subjects in each group and data was collected over a one year period. Baseline demographic data was not different between groups. There was a significant difference between the groups for maximal sensory block height achieved (Group 7 = T-2, Group 8 = T-2 and Group 9 = T-1, P=0.02) as well as the time to reach this maximal block height (Group 7 = 6.9 min., Group 8 = 8.3 min. and Group 9 = 10.5 min., P = 0.01). The time to reach T-4 was not statistically significant between groups. All subjects had adequate anesthesia for surgery, and all patients achieved a maximum Bromage score of 3. All of the patients had an adequate level of anesthesia for delivery of the baby, but 25% of subjects required supplementation of the block via the epidural catheter before conclusion of surgery. There were eight patients in Group 7 who required supplementation, four patients in Group 8, and three patients in Group 9 (P = 0.16). The time to a motor block recovery to a Bromage score of 2 was not different between groups. There were no significant differences in the incidence of hypotension or the use of vasopressors. There were also no differences in the incidence of side effects such as nausea, vomiting, or shivering. There was one inadvertent dural puncture and three inadvertent venous punctures. All subjects were included in the final analysis according to the intention to treat principle.

Conclusion            This study was designed to evaluate the differences in the block with varying dosages of bupivacaine. There was a difference in the maximal block height, but since all of the groups achieved an adequate block height for cesarean delivery (> T-4), this may not be a clinically significant finding. The incidence of hypotension was a significant finding in all of the groups, and it appeared to be dose-dependent. The need for supplementation with the epidural was 15/60 overall, and eight of those subjects were from Group 7. The decreased dosage (7 mg) resulted in a decreased risk of maternal hypotension, but it also resulted in an increased requirement for supplementation.

 

Comment

This is an interesting article to discuss because the incidence of spinal-induced hypotension is a significant issue in the obstetric population. I think that it’s interesting that multiple studies have demonstrated that the spinal level achieved after a combined spinal-epidural is higher than a single shot spinal, even when the epidural is not used at all.1-3  The mechanism for this is not completely understood, but it may be a useful side effect that allows the provider to decrease the spinal dosage and the associated cardiovascular consequences. However, this study did not find a difference in the incidence of hypotension or the use of vasopressors, so this effect may not be clinically significant.

The solution of bupivacaine used in this study is slightly different than the preparation I have used in the United States. We often use 0.75% bupivacaine in dextrose which is the preparation packaged in the spinal kit. This preparation would be difficult to measure 7 mg vs. 8 mg. This would also make it difficult to replicate this study, and I’m unsure of the difference in spread of the local anesthetic with a different preparation.

The other important thing to discuss about this study was that the average height of the women was 62.2 - 63.0 inches, which is less than the average height here in the United States. The dosages may not produce the same result in a woman from this country.

I think it is unwise to change your practice based on the results of this study. The motivation to minimize side effects of the spinal is an understandable goal, but the scenario of an inadequate level and the risk of an ill-positioned (and unproven) epidural catheter may lead to an unanticipated general anesthetic. This risk highlights one of my dislikes of the technique of the combined spinal-epidural, which is that the back-up plan is a completely unproven catheter. The fact that 25% of subjects in this study required the use of supplemental epidural bupivacaine has only strengthened my feeling that 10.5 – 11.25 mg is a reasonable dosage for the average height parturient.

 

Lisa Osborne, PhD, CRNA

 

 

1.     Turhanoglu S, Kaya S, Erdogan H. Is there an advantage in using low-dose intrathecal bupivacaine for cesarean section?  J Anesth 2009;23:353-7.

2.     Goy, RW, Sia, AT. Sensorimotor anesthesia and hypotension after subarachnoid block: combined spinal-epidural technique. Anesth Analg 2004;98:491-6.

3.     Ithinin, F. Lim Y. Sia AT, Ocampo, CE. Combined spinal epidural causes higher level of block than the equivalent single-shot spinal anesthesia in elective cesarean patients. Anesth Analg 2006;102:577-80.

 

 

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 12, December 31, 2009




Patient Safety

Judge A, Fecho K


 

 

Lateral antebrachial cutaneous neuropathy as a result of positioning while under general anesthesia

Anesth Analg 2010;110:122-124

Judge A, Fecho K

 

 

Abstract

Purpose            The purpose of this case report was to describe a positioning injury to the lateral antebrachial cutaneous nerve.

Background            The Lateral Antebrachial Cutaneous Nerve (LABCN) provides sensation to the radial aspect of the forearm. It arises from the musculocutaneous nerve, which, in turn, originates from the nerve roots of C-5 to C-8. The LABCN runs under the biceps tendon in the antecubital space where it is vulnerable to injury. Distal to that point, it provides sensation to the radial aspect of the forearm.

LABCN injury has been reported from tourniquet compression, a restraining strap, and, rarely, an improperly applied blood pressure cuff. Tourniquet compression probably requires at least 200 torr pressure and more often affects the radial nerve. LABCN injury is often associated with the triad of prolonged abduction, extension, and external rotation at the shoulder. Positioning an arm on an arm board that is not as tall as the OR table it is attached to, so that a drop off exists between the OR table and the arm board, may predispose to this injury.

Methodology            An ASA class I, 25 y/o, 111 kg male underwent a six hour knee procedure in the supine position with general anesthesia. The blood pressure cuff was properly positioned on the right arm and cycled every five minutes. His arms were placed on arm boards, abducted <90° at the shoulder, palms up (supination), and secured. Postoperatively he complained of right arm weakness and intermittent paresthesia. An area of paresthesia and anesthesia was mapped over the radial aspect of his forearm extending from the antecubital fossa to the thumb. In postoperative discussions the patient stated that he was somewhat uncomfortable with his arms completely extended.

Result            A comprehensive exam showed minor weakness and no signs of ongoing nerve injury. On postop day one the paresthesia was improved but still present. The patient was discharged home with instructions to rest the arm, apply ice, and take nonsteroidal antiinflammatories. In a recheck by phone postop day four the patient reported a complete recovery.

Conclusion            In this case, patient positioning most likely resulted in compression and/or stretching of the LABCN during the six hour general anesthetic, resulting in neuropathy. Ideally, patients should be positioned with minimal abduction, extension, and external rotation at the shoulder. Patients with restricted range of motion should not be positioned beyond their range of comfortable motion.

 

Comment

The 1999 ASA closed claims analysis tells us that 16% of claims involved nerve injury. While that doesn’t tell us much about the overall incidence of upper extremity nerve injury it does say something about the importance to patients. This case could have happened to one of my patients. It appears that the patient was positioned properly but for some unknown reason was vulnerable to nerve injury. It is likely that the injury would not have occurred if the case had been only an hour or two long. The BP cuff may have contributed to the injury but it was only set to cycle every five minutes. I normally set the BP machine for every three minutes during a general anesthetic. The only thing that might have prevented the injury would have been positioning the arms so that they were slightly flexed at the elbow during the procedure. Postoperatively the patient said his arms were never comfortable when completely extended. It is easy to see how this information could be missed in a busy preop holding area.

This report reminded me of two things, the importance of talking to patients about their comfort in the position I intend to place them in during their procedure and the risk factors for nerve injuries in the upper extremity.

 

Michael Fiedler, PhD, CRNA

 

Cheney FW, Domino KB, Caplan RA, Posner KL. Nerve Injury Associated with Anesthesia: A Closed Claims Analysis. Anesthesiology 1999;90:1062-9.

 

 

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 12, December 31, 2009




Regional Anesthesia

Asik I, Kocum AI, Goktug A, Turhan KSC, Alkis N


 

 

Comparison of ropivacaine 0.2% and 0.25% with lidocaine 0.5% for intravenous regional anesthesia

J Clin Anesth 2009;21:401-407

Asik I, Kocum AI, Goktug A, Turhan KSC, Alkis N

 

 

Abstract

Purpose            The purpose of this study was to compare the onset, efficacy, and postoperative analgesia of intravenous regional anesthesia with 0.5% lidocaine, 0.2% ropivacaine, and 0.25% ropivacaine.

Background            Ropivacaine is an amide local anesthetic structurally similar to bupivacaine. Ropivacaine has a similar duration of action but less toxicity than bupivacaine. Ropivacaine is also about 50% less lipid soluble than bupivacaine. Conversely, ropivacaine is more lipid soluble than lidocaine and has greater protein binding. In a small number of subjects, ropivacaine 0.2% and 0.375% has been shown to produce Intravenous Regional Anesthesia (IVRA) equivalent to lidocaine 0.5% with persistent postoperative analgesia. One study has reported fewer CNS side effects in patients who received ropivacaine for IVRA rather than lidocaine. The optimal concentration of ropivacaine for IVRA is unknown.

Methodology            This prospective, double-blind, randomized study included healthy adult patients scheduled for forearm and hand procedures less than one hour in duration. Subjects were randomly assigned to receive IVRA with 0.5% lidocaine (100 mg total dose) or 0.2% or 0.25% ropivacaine (80 mg or 100 mg total dose respectively). The IVRA was performed the same way in all three groups. The tourniquet was inflated to at least 100 mm Hg above baseline systolic blood pressure. Local anesthetic volume was 40 mL in all groups. Onset of analgesia was assessed in the distribution of the radial, median, ulnar, and musculocutaneous nerves. During the procedure, fentanyl 0.5 µg/kg and midazolam 1 mg – 4 mg were administered as needed for tourniquet pain. The tourniquet remained inflated for a minimum of 30 min after local anesthetic injection even if surgery was completed more quickly. The tourniquet was deflated for 30 seconds, then reinflated for 60 seconds, then deflated permanently. After tourniquet deflation, patients were assessed for cardiac arrhythmias and CNS toxicity. Postoperative pain scores were reported by patients verbally on a 0 to 10 scale at 10 minute intervals.

Result            Although 66 patients were enrolled in the study, data was collected on only 61. The other 5 (7.6%) were excluded due to an inadequate block; 2 in the lidocaine group, 2 in ropivacaine 0.2% group, and 1 in the ropivacaine 0.25% group. There were no differences in demographic variables, duration of surgery, tourniquet time, or onset of anesthesia between groups.

Following tourniquet deflation, signs of CNS toxicity were reported by 8 patients in the lidocaine group, 2 in the ropivacaine 0.2% group, and 3 in the ropivacaine 0.25% group. No arrhythmias or hypotension was observed. The first pinprick sensation returned in a median time of 3.5 ± 1.1 min in the lidocaine group, 20.5 ± 4.6 min in the ropivacaine 0.2% group, and 23.5 ± 4.8 min in the ropivacaine 0.25% group. Verbal pain scores were significantly lower in both ropivacaine groups than the lidocaine group on admission to the PACU and remained so through the 20 minute assessment. At 30 minutes, verbal pain scores were nearly identical in all three groups. The number of patients who received pain medicine in the PACU was higher in the lidocaine group than in either of the ropivacaine groups (P<0.05).

Conclusion            Ropivacaine IVRA was as effective as IVRA with lidocaine but produced better postoperative analgesia. The higher concentration of ropivacaine may further improve postoperative analgesia. The safety of ropivacaine IVRA cannot be determined by this study.

 

Comment

This is interesting but I’m not ready to start doing Bier blocks with ropivacaine to get 20 minutes of enhanced analgesia postoperatively from the block. When they got to the PACU lidocaine patients rated their pain about an “8” while ropivacaine patients rated their pain a “1.” That is an impressive and unexpected difference, I’ll grant you. At the 30 minute assessment all groups rated their pain about the same so we only know that the effect lasted for 20 minutes. But there are other ways I can control postoperative pain. I don’t have a problem with Bier blocks now that needs solving. I do, however, have concerns about the toxicity of ropivacaine. Ropivacaine is certainly much less toxic than bupivacaine, but I don’t use bupivacaine for Bier block precisely because of it’s toxicity. And ropivacaine certainly is more toxic than lidocaine. Now, later on we may learn that ropivacaine is absorbed by the tissues during a Bier block and doesn’t reenter the circulation fast enough to produce toxicity. But just occasionally, the tourniquet fails right after I’ve finished injecting the local anesthetic (been there). While a rare event, I think the margin of safety is greater with the continued use of lidocaine for Bier blocks.

 

Michael Fiedler, PhD, CRNA

 

 

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 12, December 31, 2009