ISSN NUMBER: 1938-7172
Issue 3.2

Michael A. Fiedler, PhD, CRNA

Contributing Editors:
Mary A. Golinski, PhD, CRNA
Alfred E. Lupien, PhD, CRNA
Steven R. Wooden, MS, CRNA

Guest Editor:
Terri M. Cahoon, MSN, 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











Timmermann A, Cremer S, Eich C, Kazmaier S, Br?uer A, Graf BM, Russo SG



Prospective clinical and fiberoptic evaluation of the supreme laryngeal mask airway

Anesthesiology 2009;110:262-265

Timmermann A, Cremer S, Eich C, Kazmaier S, Bräuer A, Graf BM, Russo SG




Purpose            The purpose of this evaluation was to assess ease of insertion, describe the position of the LMA in the airway, measure the leak pressure during positive pressure ventilation, and record any adverse events associated with its use.

Background            The Laryngeal Mask Airway (LMA) Supreme is a new, plastic, disposable airway that combines features of several other LMA styles. The LMA Supreme has a curved shaft, a gastric vent tube, a high cuff volume, a reinforced tip, epiglottic fins, and an integrated bite block. The cuff design was also changed to ease insertion and prevent air leaks at higher peak airway pressures than other LMAs.

Methodology            This prospective, descriptive, evaluation included women undergoing elective surgery. Women with an identified risk of difficult airway management, a history of gastric reflux, or ASA physical status IV or V were excluded.

General anesthesia was induced with 2 µg/kg fentanyl and 2 mg/kg propofol and maintained with sevoflurane. The LMA Supreme was inserted with a one-handed rotational technique while the patient’s head was in a neutral position. The LMA cuff was inflated to a maximum of 60 cm H2O. If ventilation was not possible after placement, one additional attempt was permitted before withdrawing the patient from the evaluation. Time for LMA insertion was measured from removal of the face mask to the presence of a capnography waveform. After placing the LMA, a 14-French gastric tube was inserted through the gastric drain. Next the leak pressure was measured during positive pressure ventilation. A fiberscope was then advanced through the LMA to categorize the laryngeal view. Laryngeal view was assessed a second time at the end of surgery to determine whether or not the LMA position had remained stable during the case. Optimal LMA position was defined as the following three findings: 1) the tip of the LMA was posterior to the arytenoids, 2) the epiglottis was visible and not folded down into the airway, and 3) the vocal cords were visible upon fiberscopic examination. Approximately two hours postoperatively, patients were surveyed about the presence or absence of a sore throat, difficulty swallowing, or hoarseness.

Result            A total of 100 patients were enrolled. One patient was omitted from analysis because the LMA was too large to be inserted. Patients ranged in age from 19 years to 88 years old. Their average body mass index (BMI) was 25.9 kg/m2 (range 17 to 41.5). Ten patients had a BMI greater than 35 kg/m2. The surgical procedures lasted an average of 64 minutes (range 11 to 180 min).

The LMA Supreme was placed in one attempt in 94% of patients. The average time for placement was 10 seconds (range 8 to 30 sec). Initial attempts at ventilation were all “adequate.” The gastric tube was inserted in one attempt in all patients. Fiberoptic evaluation of LMA position was rated “optimal” in all patients immediately after placement and at the end of surgery. The average volume needed to inflate the cuff to 60 cm H2O was 18.4 mL (range 8 to 31 mL). The mean pressure needed to cause an air leak during positive pressure ventilation was 28.1 cm H2O (range 21 to 35 cm H2O). After removing the LMA, blood was visible either inside or outside the cuff in 10 patients (10.1%). Eight patients (8.1%) reported a sore throat that was 3 or less on a visual analogue scale of 0 – 10. No patient reported dysphagia or dysphonia.

During fiberoptic assessment of LMA position, a narrowing of the vocal cords was observed in 11 patients (11.1%). In 3 of these patients increased inspiratory pressure was needed for ventilation. In 2 other patients an inspiratory stridor was audible. In all cases the surgical procedure was continued with no change in airway management.

Conclusion            The LMA Supreme was typically correctly inserted in about 10 seconds resulting in at least adequate ventilation and preventing air leaks up to an average 28 cm H2O airway pressure. Gastric tubes were placed in all patients on the first attempt. A few patients developed early postoperative sore throat but none developed difficulty swallowing or speaking. About 11% of patients developed airway narrowing that lead to increased airway resistance and / or inspiratory stridor.



This is the second report I have seen describing an airway narrowing and, in some cases, difficulty with ventilation associated with proper placement of the LMA Supreme. (See page 17 in the January issue of Anesthesia Abstracts for a previous case report; reference below.) The previous case report left me saying, “We’ll have to watch and see if airway obstruction is a problem with the LMA Supreme.” Often times case reports find a one time event that does not represent a clinical problem. In this case, however, it is starting to look like they may have been on to something. In this evaluation just over 11% of patients had visible narrowing of the airway and 5 of those (5% of all patients) experienced some difficulty with airflow as a result.

It is still difficult to determine if this represents a clinical problem but I am growing more suspicious. What the authors report sounds like a problem but they also finished the cases without any change in airway management. I’m scratching my head. One thing is for certain, though. If there is a clinical problem with 11% of LMA Supreme uses that cannot be solved with some change in technique, there is a problem with the device and I won’t be too interested in using it.


Michael Fiedler, PhD, CRNA


Kleine-Brueggeney M, Theiler LG, Luyet C, Greif R. Acute airway obstruction caused by the new single use laryngeal mask airway supreme. Anesthesiology 2009;110:189-190. (Abstract and comment in the January 2009 issue of Anesthesia Abstracts.)


If you have used the LMA Supreme please share your experience in regards to airway narrowing or increased airway resistance with other Anesthesia Abstracts readers via the “Blog with the Editors” link.

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 2, February 28, 2009


Yost S, McDonald B, Vallejo M



anesthetic management of a pregnant patient with an automatic implantable cardioverter-defibrillator: a case report

AANA J 2009;77:29-32

Yost S, McDonald B, Vallejo M




Purpose            This article presented a case report which concerned anesthesia technique selection for an obstetric patient who had an automatic implantable cardioverter-defibrillator.

Background            Automatic implantable cardioverter-defibrillators (AICD) are being used more frequently, saving lives, and being seen in more surgical and obstetric patients.

Methodology            The case presented involved a 33 year old woman at 37.5 weeks gestation admitted for an elective induction. The patient had tetrology of Fallot repaired at 10 months of age and subsequently developed syncope secondary to malignant ventricular arrhythmias in her 20s. She was treated successfully with the implantation of a dual chamber automatic implantable cardioverter-defibrillator. The patient’s AICD subsequently recorded 31 ventricular fibrillation events with AICD activation.

The obstetric and anesthesia teams were concerned that the stress of labor and vaginal delivery might promote the development of malignant tachycardia. A Valsalva maneuver can cause decreased preload, decreased cardiac output, decreased blood pressure, and reflexive tachycardia. For that reason it was decided the safest approach for this particular patient was to use epidural anesthesia and forceps-assisted vaginal delivery. The cardiologist recommended that the AICD be inactivated to prevent accidental discharge during labor. External defibrillator pads were placed on the patient in case a malignant dysrhythmia would occur while the AICD was inactive.

When the epidural catheter was placed, the routine test dose of lidocaine with epinephrine was omitted in order to prevent the possibility of tachycardia if the catheter was indeed in a vessel. The catheter was aspirated without indication of blood and a test dose of 0.1% ropivacaine was added to test for intrathecal placement. The anesthesia provider was comfortable that the catheter was placed properly and then administered 100 µg of fentanyl and 8 mL of 0.1% ropivacaine through the epidural catheter followed by an infusion of 0.1% ropivacaine and 2 µg/ml of fentanyl at 12mL/hr. Delivery was accomplished with forceps assistance and there were no cardiovascular or anesthesia complications.

Result            There were several concerns surrounding the management of this patient. Although she had been living a healthy life with the assistance of the AICD, anatomical and physiological changes during pregnancy, labor, and delivery could have created difficulties. These potential problems included lead dislodgement, lead fractures, pressure on the pulse generator created by the expanding abdominal cavity, and accidental discharge of the AICD during labor secondary to autonomic nervous system changes. There have been eleven reports of AICD discharge during pregnancy and in each case no fetal complications were found. The most significant risk to the fetus from AICD discharge is thought to be decreased placental perfusion because of maternal hypotension. If maternal hypotension would have occurred, the plan was to use an alpha agonist such as phenylephrine which would be less likely than ephedrine to cause tachycardia.

Conclusion            The underlying cardiac disease is more important in the management of patients with an AICD than the fact that they have such a device. Although the cardiologist in this case suggested that the AICD be deactivated, literature supports leaving the AICD on unless a cesarean delivery is planned where electrocautery might be used. Anesthesia plans for patients with an AICD should include methods to avoid tachycardia. Epidural and spinal analgesia reduce catecholamine release but should be carefully managed to avoid reflex tachycardia secondary to hypotension.



I have seen more patients with AICDs in the last two years than I have seen in my 26 years of practice. I suspect we will continue to see more of them in time and become more comfortable with managing them, but in the mean time I continue to worry about accidental discharge and the effect it might have on the patient’s cardiovascular status so most of them are inactivated with the exception of minor and diagnostic procedure where electrocautery is not used.

This was an interesting case study and brought to light a unique situation where multiple patient and environmental factors could complicate the anesthetic management. I agree that the underlying cardiovascular problem should be the focus of the anesthesia management with secondary consideration to the fact that the patient has an AICD. The choice not to use a test dose of epinephrine was an interesting one. I would agree that a short period of tachycardia would have resulted from a positive vascular placement, but that probably would be more manageable than the effects of a toxic vascular infusion of anesthesia agent. I have aspirated epidural catheters without blood return that have later been identified as being placed in the vascular system. Perhaps there is an adequate alternative to epinephrine in the identification of an epidural catheter placed in the vascular system. Each situation is different and the risks and benefits of administering any medications or withholding the administration of medications should be considered each time. I can understand their concern in this case, but I probably would have still verified placement with a test dose after using every other method while being prepared to deal with the potential consequences of tachycardia.

It appears that in labor and delivery, inactivation is probably not necessary but having a magnet available just in case a problem with the device should arise is not a bad idea.


Steven R Wooden, MS CRNA



© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 2, February 28, 2009


Hsieh M-H, Chen T-L, Lin Y-H, Chang C-C, Lin C-S, Lee Y-W



Acute pulmonary edema from unrecognized high irrigation pressure in hysteroscopy: a report of two cases

J Clin Anesth 2009;20:614-617

Hsieh M-H, Chen T-L, Lin Y-H, Chang C-C, Lin C-S, Lee Y-W




Purpose            The purpose of this report was to describe two cases of pulmonary edema during hysteroscopy due to equipment failure and excessive irrigation pressure.

Background            Hysteroscopy is performed for both diagnostic and operative procedures. During hysteroscopy the uterus is distended with fluid to aid in visualization. Complications of uterine distension and hysteroscopy are rare. Known risks include introduction of distension fluid into the vascular system by infusion and/or absorption, intravascular volume overload, pulmonary edema, and congestive heart failure. Distension fluid may enter the circulation through open vessels exposed during surgical resection, absorbed by the uterus, or enter the abdomen through the fallopian tubes where it is easily absorbed. Irrigation pressure, open vessels, duration of surgery and other factors determine the extent of irrigant absorption.

Methodology            This report described pulmonary edema in two woman following operative hysteroscopy. The first woman was 40 years old, 65 kg, and had normal preoperative hemoglobin concentration and vital signs. Her procedure lasted 40 minutes. The second woman was 29 years old, 54 kg, and also had normal hemoglobin concentration and vital signs. Her procedure lasted 90 minutes. In both cases general anesthesia was induced with fentanyl, lidocaine, propofol and succinylcholine. The airway was managed with an LMA. Anesthesia was maintained with sevoflurane in oxygen. In both cases the uterus was distended with 10% dextrose solution under pressure from a pneumatic pressure infuser. In the first patient the pressure infuser was set to 100 mm Hg; in the second it was set to 75 mm Hg.

At the end of both surgeries the women had a fall in SpO2; they produced pink, frothy sputum; and chest x-ray showed pulmonary edema. In patient one this occurred in the operating room; in patient two it was discovered in the PACU.

Result            Both women were treated with 100% oxygen (via endotracheal tube in the first woman), furosemide (Lasix) administration, and appropriate supportive measures. Subsequent calculations suggested that patient one had absorbed approximately 1 liter of 10% dextrose distension fluid and patient two approximately 2 liters. Both recovered uneventfully and were discharged the next day with no further complications.

Subsequent to these complications the pneumatic pressure infuser was checked and the pressure gauge was discovered to be underreporting the pressure applied to the 10% dextrose irrigation bags by half. Thus, the actual pressure applied to the bags was 200 mm Hg and 150 mm Hg respectively.

Conclusion            Proper irrigation pressure and careful tracking of irrigation fluid input and outflow are necessary to avoid the complication associated with absorption of irrigation fluid during hysteroscopy. Accurate measurement of actual intrauterine pressure during distension is also beneficial.



I think these case reports pretty much speak for themselves. While hysteroscopy is often a fairly straightforward anesthetic and complications are rare, there is the potential for significant complications.

As always, vigilance is key.

In one of these cases a 2000 mL deficit between the irrigation fluid going in and what came out was recorded during the case, yet apparently wasn’t picked up on as a problem. The erroneous reading on the pressure transducer might be hard to discover during the case, but a 2000 mL discrepancy in the I&O should not be if one was paying attention (no sophisticated monitoring needed). Sometimes our expertise is demonstrated by meticulous attention to what is going on during a routine case that will “never” result in a problem so that the one time there is a problem we have dealt with it before it causes harm. Fortunately, in these cases, the patients recovered fully.


Michael Fiedler, PhD, CRNA



© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 2, February 28, 2009

Andrzejowski J, Hoyle J, Eapen G, Turnbull D


Effect of prewarming on post-induction core temperature and the incidence of inadvertent perioperative hypothermia in patients undergoing general anaesthesia

Br J Anaesth 2008;101:627-631

Andrzejowski J, Hoyle J, Eapen G, Turnbull D



Purpose            The purpose of this study was to evaluate the effectiveness of prewarming for preventing a decrease in core temperature during general anesthesia.

Background            Hypothermia during general anesthesia is a common problem. Hypothermia is associated with an increased incidence of myocardial ischemia, wound infections, coagulopathy, longer hospital stays, and greater costs. Hypothermia occurs due to a combination of reduced heat production, increased heat loss, and redistribution of thermal energy from the core to the periphery. Thermal redistribution begins immediately after induction of general anesthesia and may result in a decrease in core body temperature of up to 1.6°C. Redistribution of thermal energy immediately after induction of general anesthesia is difficult to prevent and even the most effective measures are often unable to avert hypothermia during short procedures. Some studies of warming before induction of general anesthesia have shown a reduction in the magnitude of hypothermia early in the case. Critical review of these studies has left doubt as to the strength of their conclusions.

Methodology            This prospective, randomized study included healthy adults undergoing general anesthesia for elective spinal surgery. Preoperative core temperature was measured with a temporal artery scanner. Intraoperative temperature was measured with an esophageal temperature probe. The device used for warming was the Arizant Healthcare “Bair Paws” forced air warming system. Patients in both groups had a warming gown applied rather than a traditional hospital gown. The warmed group had warm air from a portable warming device blown into the gown preoperatively. The warming devices were set at 38°C throughout the study. The control group wore the warming gown but received no forced air warming preoperatively. All patients received normal forced air warming intraoperatively with warming devices set at 38°C. IV fluids were not warmed. General anesthesia consisted of an infusion of propofol and either remifentanil or alfentanil. (Two patients in each group received sevoflurane for maintenance.)

Result            Seventy-six patients were enrolled in the study but 8 procedures were cancelled. In all, 31 patients were included in the prewarmed group and 37 in the control group. Patient demographics, room temperature in the OR, patient core temperature immediately after induction of general anesthesia, volume of IV fluid infused, and gender were not significantly different between groups. The average prewarming interval prior to surgery was 72 minutes. There was no association between the duration of prewarming and the magnitude of temperature decline in the prewarmed group during surgery.

After induction of general anesthesia the fall in core temperature was smaller in the prewarmed group at 40, 60, and 80 minutes post-induction (P ≤ 0.05). Comparing the area under the curve for temperature in both groups over time, the prewarmed group was warmer than the control group (P < 0.005). Throughout the case, 68% of prewarmed patients but only 43% of control patients, were > 36°C. Three patients in the control group were < 36°C immediately after induction and more control patients than prewarmed patients were hypothermic at all data collection times throughout the study.

Conclusion            Prewarming healthy patients with a “Bair Paws” forced air warming gown for an average of 72 minutes prior to general anesthesia and spinal surgery resulted in a smaller drop in core body temperature between 40 minutes and 80 minutes after induction of general anesthesia. Prewarming also resulted in an overall decrease in the number of patients who became hypothermic throughout the duration of the procedure.



Hypothermia due to general anesthesia and surgery is a problem that has long needed to be taken more seriously. Hypothermia is associated with very real morbidity and even mortality and there is more we can do to prevent it than we regularly do. However, we face a couple difficult problems in preventing hypothermia. The first is that hypothermia can start before the induction of general anesthesia. I often place an esophageal probe immediately after induction only to find that the patient is already hypothermic or nearly hypothermic. One of the reasons for this is that defending a normal body temperature is partly behavioral. When a person begins to feel cold they move to a warmer location, dress more warmly, or complain to someone that it is too cold. Sufficiently sedated patients don’t do these things. Worse yet, the benzodiazepines we use to reduce preoperative anxiety are vasodilators. Midazolam has been shown to begin reducing patient temperature before induction of general anesthesia.1 The second problem we face is that redistribution core hypothermia during the initial 60 to 90 minutes of a case is quite difficult to prevent.

Prewarming may help us with both problems. Past studies, though, have not convincingly shown a way to make prewarming work. I did a prewarming study of my own in the 1990’s and, like Thomas Edison, simply learned another way that didn’t work. The present rather well designed study did show some benefit to prewarming. I’m encouraged by the results. One reason they may have had success was that they didn’t turn the temperature up too high during prewarming. (I probably would have set the temperature higher during the case.) During my prewarming study I had patients start with the forced air warmer set as high as they could stand. It wasn’t long before many of them were too hot and either withdrew from the study or turned the warmer off.

One limitation to applying the information in this study is that it may be difficult to prewarm for an hour or longer in some practice settings. Nevertheless, I’m anxious to see more information on this prewarming technique. With a little fine tuning it may really help our patients.


Michael Fiedler, PhD, CRNA


1. Matsukawa T, Hanagata K, Ozaki M, Iwashita H, Koshimizu M, Kumazawa T. IM midazolam as premedication produces a concentration-dependent decrease in core temperature in male volunteers. Br J Anaesth. 1997;78:396-399.


© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 2, February 28, 2009

Ghosale G, Shah V

Combined spinal-epidural anesthesia for renal transplantation

Transplant Proc. 2008;40:1122-1124

Ghosale G, Shah V



Purpose            The purpose of this study was to assess patient outcomes, and conduct an anesthesia provider review of the experience, after performing combined spinal-epidural anesthesia for renal transplant surgery. In addition to the customary demographic variables, data was collected on the intra-operative anesthetic course, hemodynamic changes during the procedure, efficacy of post-operative analgesia, and associated complications.

Background            End-stage renal disease affects virtually all body systems. Those undergoing renal transplantation present with a unique set of problems for the anesthetist to address. It has been reported that regional anesthesia is not always adequate for renal transplantation for a plethora of reasons and a variety of problems have been reported. There also exists a fear of hematoma formation after epidural placement in these individuals, as well as a fear of worsening peripheral neuropathy. If the cases do not run smoothly, and surgical interventions are prolonged, the question becomes whether or not a protracted procedure should be performed with a regional technique. There have been case studies cited in which continuous epidural blocks alone do not provide adequate surgical conditions, often necessitating the conversion to general anesthesia. Combined spinal-epidural anesthesia has recently gained widespread acceptance for prolonged major surgery below the level of the umbilicus.

Methodology            Patients scheduled for elective renal transplantation were enrolled in this prospective, non-randomized, descriptive study. All agreed to combined spinal-epidural anesthesia. Patients were excluded who had abnormal coagulation profiles, peripheral neuropathy, or myopathy at the time of surgery. Patients were hemodialyzed within 24 hours prior to the procedure, and hypertension was controlled with antihypertensive agents. Standard pre-operative laboratory blood values were obtained.

Combined spinal epidural anesthesia was performed. The epidural needle and catheter were placed at the L3-L4 interspace and the spinal needle was inserted at the L4-L5 interspace. Through the spinal needle, 0.5% (15-20 mg) bupivacaine was administered. Approximately 90 minutes after the spinal bupivacaine was injected, a mixture of 0.5% bupivacaine and 2% lidocaine with epinephrine was administered through the epidural catheter. Additional epidural bolus doses of local anesthetic mixture were administered every hour until culmination of the surgery. All patients had routine intra-operative monitoring and CVP monitoring. Clinically significant hypotension was defined as >30% drop from baseline systolic and diastolic values. Hypotension was treated with ephedrine. Bradycardia was defined as a pulse rate of < 50 beats/min and if this occurred atropine was administered. Central venous pressures were kept between 12 and 15 mmHg with crystalloids, colloids, and blood products. Patients were sedated with midazolam and could respond to verbal commands throughout the procedure.

The epidural catheter was used to provide post-operative pain management. Buprenorphine 1.5 mcg/kg every 12 hours for 48 hours post-operatively was injected through the catheter. A visual analogue pain scoring technique was used to rate the post-operative pain expressed by the patients. All intra-anesthetic and post-operative complications were documented.

Result            Fifty patients (n = 50) were enrolled in the study; living donor grafts were used in 42 patients. Four patients were converted to general endotracheal anesthesia secondary to prolonged surgical time or surgical technical problems. Demographic and anesthesia parameters measured were as follows (expressed as mean values + standard deviation):

Age (years)

37.06 + 8.6

Weight (kg)

57.44 + 10.83

Total surgical time (min)

212 + 42

Dose of 0.5% spinal bupivicaine (mg)

17.65 + 1.06

Intra-operative fluids (mL/kg)

64.21 + 12.3

MAP before reperfusion (mm Hg)

109 + 14

MAP after reperfusion (mm Hg)

102 + 13

CVP before reperfusion (mm Hg)

13 + 2.5

CVP after reperfusion (mm Hg)

11 + 3

Three (n = 3) patients developed hypotension and two patients developed bradycardia after spinal bupivacaine was administered; both required treatment. Average urinary output intra-operatively was 8 + 0.4 mL/kg/h. Post-operatively, buprenorphine appeared to offer good analgesia as expressed by a mean VAS score of < 3. There were no post-operative complications related to the regional technique itself.

Conclusion            For this group of patients, combined spinal-epidural anesthesia for the operative anesthesia, and epidural analgesia for the management of post-operative pain, was very successful. Minimal to no serious complications were noted. Patients treated for hypotension and bradycardia post-spinal administration were not seriously affected and responded to medications administered.

Comment            Combined spinal-epidural anesthesia for renal transplantation surgery worked very well for this particular group of individuals. While the sample size was small and the patients were appropriately selected (for example, absence of symptomatic coagulopathies, dialysis completed within 24 hours of the procedure), it also appeared to be a sample without any physiologic or physical features that may have made a regional technique uniquely challenging such as difficult to control hypertension or obesity. What would have been helpful would be specifics regarding the cardiovascular indices, including medications, of the subjects. In other words, while we all know the complexities of those who suffer from end-stage renal disease, was the success of regional anesthesia for this group skewed because they were on the ‘healthier-side’ of those with renal failure? It would be easier to assess the evidence knowing the cardiovascular parameters of the sample. It certainly would assist us in our decision-making when the anesthetic choice is necessitated.

Mary A. Golinski, PhD, CRNA

Buprenorphine is an opioid agonist-antagonist analgesic. Its analgesic effect is caused by binding to opiate receptors in the central nervous system. Its antagonist effects decreases the abuse potentials  Approximately 96% of the drug is protein bound; 30% is excreted in the urine and 69% is excreted in the feces. The half life is 37 hours.

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 2, February 28, 2009

Ghoneim MM, Block RI, Haffarnan MMathews MJ

Awareness during anesthesia: risk factors, causes and sequelae: a review of reported cases in the literature

Anesth Analg 2009;108:527-535

Ghoneim MM, Block RI, Haffarnan M, Mathews MJ



Purpose            The purpose of this study was to analyze a large number of case reports of awareness during general anesthesia and compare them to control patients who did not experience awareness.

Background            Awareness during general anesthesia is uncommon and the incidence of awareness appears to have decreased over time. Studies from the 1960s and 1970s reported the incidence of awareness at 1.2% and 0.8% of all general anesthetics respectively. More recently, the incidence has been reported to be 0.007%, 0.1% and 0.2% overall. It is difficult to establish a true incidence of awareness during general anesthesia because the event is rare, awareness can be time consuming to detect, and awareness is sometimes difficult to confirm. Insufficient information exists with which to identify causes of and risk factors for awareness. Such information is, however, needed to develop strategies for preventing awareness.

Randomized, controlled trials to establish the true incidence of awareness during general anesthesia and identify its causes are probably impossible. This is due not only to ethical concerns, but also to the low incidence of the event (requiring extremely large numbers of study cases), and the inability to randomize clinical events that cannot be controlled or known in advance. An alternative strategy to study the problem is to aggregate case reports of awareness. Case reports can sometimes provide greater insight into rare events than prospective studies.

Methodology            The authors searched PubMed for English language, peer reviewed, case reports of “Awareness” and “Anesthesia” from 1950 and August 2005. Pediatric cases, cases with 60% or more missing data, cases of “out of body” experiences, dreams, and cases presenting weak evidence for awareness were excluded.

Data from each case was collected independently by two different investigators and compared for completeness and accuracy. Case data was compared with two different groups of data from patients who did not experience intraoperative awareness and included over 20,000 control patients.

Result            A total of 271 case reports were discovered; 75% of which were published since 1990. Most cases of awareness, 74%, occurred during maintenance of general anesthesia. A history of awareness during a previous general anesthetic was present in 1.6% of awareness cases. Difficult and prolonged laryngoscopy and intubation was present in 4.5% of awareness cases. Patients who experienced awareness were younger and more likely to be female than patients from one, but not the second, database of control patients. There was no difference between awareness and control patients in the areas of weight, body mass index, use of nitrous oxide, or use of muscle relaxants.

Awareness patients were more likely than control patients to have undergone cardiac or obstetric procedures (P < 0.0001). While the numbers were small, obstetric patients were over 100 times more likely to experience awareness than control patients. In contrast, cardiac patients were only 9 times more likely. Awareness patients were also more likely to have had at least one episode of intraoperative tachycardia (P < 0.0001) or hypertension (P < 0.0001). About 25% of awareness patients received no potent inhalation agent or propofol during maintenance of anesthesia.

Light anesthesia was the most frequent cause of awareness during general anesthesia; 87% of all cases of awareness. The anesthetic technique used during cases of awareness was less likely to have included premedication, used lower doses of induction and maintenance anesthetics, and lower doses of opioids compared to control patients.

Conclusion            The true incidence of awareness during general anesthesia is probably unknown. The most well established risk factors for awareness appear to be light anesthesia and a history of awareness during a previous general anesthetic. When light anesthesia is indicated, the use of amnestics such as scopolamine, benzodiazepines, or ketamine should be considered.



The authors of this study begin by making the case that there are some situations where case reports can be more influential than a properly conducted study. They make some good points about bias in assessing awareness and cite two instances where information in case reports alerted anesthesia providers to significant dangers before any studies were conducted. While the case reports they use as examples are not analogous to the way they used case reports in their study, I do agree that no study to date definitively answers our questions about the cause and prevention of intraoperative awareness.

Some anesthesia providers seem obsessed with monitoring the level of consciousness as a means to make sure awareness does not occur rather than uniformly applying what we already know about amnesia to all patients. In the near term this seems odd to me for a couple reasons. First, how do you develop a monitor for something like “consciousness” that hasn’t been defined and which can be interrupted in one of several areas of the brain. (Propofol, etomidate, and ketamine each cause unconsciousness by acting in different areas of the brain.) Second, developing and purchasing consciousness monitors is expensive. And what am I going to do if the monitor says a patient is at risk for recall? I’m going to give them more of a drug that prevents recall. Why not simply give one of those drugs to everyone and forget the monitor? This study reported that 25% of patients who experienced awareness received no inhalation agent. While they didn’t elaborate I can only assume that most of these cases were from years ago when we administered “nitrous / narcotic” anesthetics with oxygen, nitrous oxide, fentanyl, a muscle relaxant, and, perhaps, droperidol. This technique is seldom used now in favor of a potent inhalation agent and the incidence of recall is lower now as well. We know that potent NMDA receptor blockers are very effective amnestics, so why not run a very low dose ketamine infusion during almost all general anesthetics. Doing so would be inexpensive and I wouldn’t be surprised if it all but eliminated awareness.

This study has some important methodological problems. The purpose of the study isn’t clear and the control patients weren’t even moderately well “matched” to patients who experienced awareness. As a result, comparisons are hard to make. While the study doesn’t provide much new information about intraoperative awareness it does make its points by looking at the problem of awareness in a new way. Whenever we look at a problem in a new way and come up with the same answers our confidence in those answers increases. The “same answers” I see in this study are that awareness is associated with light anesthesia, cardiac procedures, and obstetric procedures. The new information I see in this study is the association of awareness with intraoperative tachycardia or hypertension. While awareness was reported in 1.6% of patients with a history of awareness and 4.5 % of patient with difficult intubations there was no comparison with the control patients. So, for all we know, control patients were even more likely to have had a history of awareness during a previous procedure or a difficult intubation. If that were the case, history of awareness and difficult intubation would certainly not be risk factors for awareness.

Michael Fiedler, PhD, CRNA

Examining a problem with several different research techniques, often simultaneously, is called “triangulation.”

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 2, February 28, 2009


Linn J, DeSilva C, Peeters-Asdourian C



Thromboembolic stroke: a rare complication associated with peri-procedural management of an epidural steroid injection

Pain Physician 2009;12:159-162

Linn J, DeSilva C, Peeters-Asdourian C




Purpose            The purpose of this article was to present a case report highlighting a rare but devastating complication of managing a patient’s anticoagulation therapy in preparation for an epidural steroid injection.

Background            An 81 year old patient with radicular pain secondary to spinal stenosis at L4-5 was scheduled for a lumbar epidural steroid injection (LESI). The patient had a previous mitral valve replacement and was taking warfarin. The patient was asked to discontinue her warfarin for 7 days prior to the LESI in order to normalize her coagulation and reduce the risk of an epidural hematoma.

The anticoagulant warfarin is commonly used to reduce the risk of thromboembolic events. As our population becomes older, we find more patients with conditions requiring warfarin therapy. Almost 10% of all people older than 80 years have atrial fibrillation. Thromboebolism is a serious risk in atrial fibrillation. A clinical tool called the “CHADS-2” is used to evaluate the risk of thromboebolism in uncoagulated patients with atrial fibrillation. It gives a score of one point to patients with congestive heart failure, hypertension, age greater than 75, and diabetes. It gives two points to patients with a history of stroke. With this tool, patients having a score of 0-2, 3-4, and 5-6 represent an annual risk of stroke at 2-4%, 6-9%, and 13-18% respectively. To reduce those risks, the American College of Cardiology suggest treating these patients with warfarin to obtain an INR of 2-3, and in patients with prosthetic heart valves the recommended INR is 3-4.

Methodology            When the patient presented for her first LESI she was disoriented and uncooperative. The LESI was cancelled and rescheduled for two days later. Her warfarin therapy continued to be held. When the patient returned to the clinic she was pleasant and fully oriented. Her International Normalized Ratio (INR) was 1.1. The LESI was accomplished without any difficulties, injecting 80 mg of methylprednisolone at the L5-S1 interspace under fluoroscopic guidance. The patient was instructed to resume her warfarin the same day.

Result            On the first post procedure day, the patient was admitted to the hospital with left sided hemiparesis and dysarthria. She was later discharged to a rehabilitation center with continuation of her stroke symptoms.

Conclusion            If therapeutic recommended levels of anticoagulation are maintained during an epidural steroid injection it would place the patient at serious risk of bleeding complications. That risk is well understood, but less understood, and often ignored, is the risk of complications resulting from normalizing a patient’s coagulation who is being treated with warfarin. It is recommended that patients having a CHADS-2 score of 3 or higher, representing an annual stroke risk of 6%, be given heparin to “bridge” warfarin therapy. The strategy includes withholding warfarin therapy for 4 days before the procedure while using heparin to maintain therapeutic levels until 12 hours prior to the procedure. Heparin allows easier control and more rapid normalization. It is recommended that heparin be used again 24 hours after the procedure in order to again bridge the therapy until the resumed warfarin becomes therapeutic.

Although the benefits of stopping warfarin therapy appear to outweigh the risk of stroke prior to epidural steroid treatment in most patients, it is prudent to consult the physician prescribing the warfarin to see if bridging therapy might be warranted.


I know of many providers that routinely discontinue anticoagulation therapy for 4 or more days prior to an epidural steroid injection and give little thought to the risks associated with discontinuing such therapy. I agree that the risks of not discontinuing therapy are significant, but this article points out we must recognize the potential problems with normalizing anticoagulation in some patients and realize that there are strategies to deal with these potential problems. It is prudent to discuss these risks with the medical staff so that everyone will be on the same page when patients at high risk for stroke are scheduled for an elective procedure that requires anticoagulation normalization.


Steven R Wooden, MS CRNA



© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 2, February 28, 2009

Pediatric Anesthesia

Voronov P, Tobin MJ, Billings K, Cot? CJ, Iyer A, Suresh S


Postoperative pain relief in infants undergoing myringotomy and tube placement: comparison of a novel regional ansthetic block to intranasal fentanyl – a pilot analysis

Pediatric Anesthesia 2008;18:1196-1201

Voronov P, Tobin MJ, Billings K, Coté CJ, Iyer A, Suresh S



Purpose            The purpose of this pilot study was to compare wake-up time, postoperative pain, and vomiting in children who received either intranasal fentanyl or a nerve block for pain relief following myringotomy and tube placement.

Background            Myringotomy and tube placement is a common surgical procedure and usually quite brief. Analgesia for this procedure needs more study. Oral and rectal NSAIDs, opioids, and intranasal fentanyl have each been used. Intranasal fentanyl has been shown to provide effective postoperative analgesia in this surgical population.

The auricular branch of the Vagus nerve, called the Nerve of Arnold, provides sensation to the external auditory meatus and the inferior aspect of the tympanic membrane. The incision for placement of ear tubes is made in the inferior part of the tympanic membrane.

Methodology            This prospective, randomized, double-blind study included children between 6 months old and 6 years old scheduled for bilateral myringotomy and tube placement.

In all patients, premedication was not routinely used. Parents were present for mask induction of general anesthesia. Anesthesia was maintained with nitrous oxide and sevoflurane. No intravenous line was started.

Fentanyl patients received 2 µg/kg intranasal fentanyl and the Nerve of Arnold was injected with 0.2 mL preservative-free normal saline bilaterally. Block patients received intranasal normal saline and the Nerve of Arnold was injected with 0.2 mL of 0.25% bupivacaine with 5 µg/mL epinephrine bilaterally. All injections were performed after general anesthesia was established.

Fifteen minutes after arrival in recovery, pain scores were assessed with the Children’s and Infant’s PostOperative Pain Scale (CHIPPS). Pain was assessed every five minutes thereafter. Rectal acetaminophen was administered if further pain relief was needed.

Result            The study included 200 patients between the ages of 1.86 months and 6.9 years old. Patient age, patient gender, and wake-up time was not significantly different between groups. There was no difference in pain scores between groups across time. There was no difference in vomiting between groups.

Conclusion            Nerve of Arnold block is as effective as intranasal fentanyl for pain relief after bilateral myringotomy and tube placement.



This article caught my eye due to the inclusion of intranasal fentanyl in the comparison group. In my pediatric practice, I utilize a combination of pre-operative acetaminophen and intraoperative intranasal fentanyl for similar myringotomy patients with anecdotally positive results. I am always looking for evidence to substantiate my practice. Indeed, this article did provide some evidence for me, but not what the authors intended.

As I read the study, a few concerns became obvious. Regarding the methodology, the ages of the children included in the study ranged from seven weeks to six years 11 months. This was outside of the range of six months to six years that was established and approved. The statistical analysis of the data was not specified in the description of the methods of the study. It appears that the data was collected and, then, the decision was made regarding how to examine it. This suggests weakness in the design. Once the method of statistical analysis was chosen, the t-test was not the best choice for the pain score measures; analysis of variance (ANOVA) would have been more appropriate for comparing groups with repeated measures. Finally, regarding the methods, the pain score measures were not initiated until 15 minutes after the procedure. The benefit of fentanyl decreasing the incidence of emergence delirium was not appreciated due to this design.

The results of this study demonstrated that this invasive block yielded essentially the same results as the intranasal fentanyl. In the discussion portion of the article, the negative side effects of systemic analgesia are mentioned as the reason for developing this novel nerve block. However, the block resulted in no less sedation causing delayed awakening, no less postoperative nausea and vomiting, and no greater analgesia than the fentanyl. The risk of performing a nerve block seems greater than the lack of benefit. Without that justification, I think it is difficult to persuade a surgeon to allow the time to perform the block for such a short case. This study did provide evidence that I could apply to my practice; however, it was related to the standard group to which the new intervention was compared.


Terri M. Cahoon, MSN, CRNA



© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 2, February 28, 2009

Ngwenyama NE, Anderson J Hoernschemeyer DG, Tobias J



Effects of dexmedetomidine on propofol and remifentanil infusion rates during total intravenous anestheia for spine surgery in adolescents

Pediatric Anesthesia 2008;18:1190-1195

Ngwenyama NE, Anderson J Hoernschemeyer DG, Tobias J




Purpose            The purpose of this study was to quantify any propofol-sparing effect of dexmedetomidine during co-administration for spinal surgery in adolescents.

Background            Spine surgery sometimes requires evoked potential monitoring. Inhaled anesthetics can interfere with evoked potential monitoring and total intravenous anesthesia (TIVA) with propofol and opioids may be used as an alternative. Propofol is known to produce dose related adverse effects during long infusions; including delayed awakening, lipemia, reduced platelet function, and “propofol infusion syndrome.” Some evidence indicates that these complications may occur to some degree even during an intraoperative infusion. The adverse effects are dose related, so, co-administration of another anesthetic that allows a reduction in the total dose of propofol may be advantageous. Dexmedetomidine is a selective α2 agonist that produces analgesia, sedation, and sympatholysis. When infused, the plasma concentration gradually increases for several hours if no bolus is administered first.

Methodology            This small, retrospective study included 12 to 21 year old patients who underwent posterior spinal fusion during a 24 month period. Anesthesia records were reviewed from a database maintained by an orthopedic surgery department. The anesthetic for study cases was provided by a single anesthesiologist using a protocol with or without dexmedetomidine.

The study included two groups, a propofol-remifentanil (PR) infusion group and a propofol-remifentanil-dexmedetomidine (PRD) infusion group. In both groups, the propofol infusion was begun at 100 µg/kg/min and titrated to target bispectral index values. Remifentanil was started at 0.2 µg/kg/min and titrated to a maximum dose of 0.6 µg/kg/min to keep the mean arterial pressure between 55 and 65 torr. Once the maximum infusion rate for remifentanil was reached, either labetalol or hydralazine was used, if needed, to control blood pressure. In the PRD group dexmedetomidine was started immediately after the induction of anesthesia at 0.5 µg/kg/h without a loading dose. The dexmedetomidine infusion was held constant throughout the anesthetic.

Result            The PR group included 12 patients while the PRD group included 24 patients. There was no significant difference in age, weight, or gender between groups. There was no significant difference in intraoperative heart rate or blood pressure between groups. The average duration of the surgical procedure was 391 ± 124 minutes (6.5 hours) in the PR group and 420 ± 123 minutes (7 hours) in the PRD group (P=not significant).

Remifentanil infusion rates averaged 0.38 ± 0.16 µg/kg/min in the PR group and 0.44 ± 0.24 µg/kg/min in the PRD group (P=0.37). Propofol infusion rates averaged 101 ± 33 µg/kg/min in the PR group and 71 ± 11 µg/kg/min in the PRD group (P=0.005) for the entire duration of the case. During the final hour of the case, when the plasma levels of dexmedetomidine had reached a steady state, propofol infusion rates averaged 97 ± 43 µg/kg/min in the PR group and 59 ± 15 µg/kg/min in the PRD group (P<0.001).

Conclusion            Adding a moderate dose dexmedetomidine infusion to propofol-remifentanil TIVA resulted in an overall 30% reduction in propofol infusion requirements.



The investigators accomplished their simply stated goal to quantify the reduction of propofol dose needed when a dexmedetomidine infusion is added to an infusion of propofol and remifentanil. Certainly, dexmedetomidine is a reasonable way to reduce the need for propofol and still produce adequate anesthetic depth without “messing up” the evoked potential monitoring. The biggest concern I have is the provision of amnesia. Certainly, we would not expect remifentanil to provide any meaningful level of amnesia. And, while dexmedetomidine provides CNS depression, analgesia, and minimal respiratory depression, it does not produce amnesia. We all depend upon propofol to provide amnesia in some situations. There is anecdotal evidence that it does a good job. What I don’t know is how low the infusion dose of propofol can go before the risk of awareness during general anesthesia emerges. Before I think too hard about how to get the dose of propofol down during a propofol / remifentanil / ± dexmedetomidine general anesthetic, I’d be thinking hard about how I was going to insure the patients were amnestic.

This was a rather unique retrospective study. Retrospective studies are generally not considered to be very robust sources of evidence. They are often considered to be about the same level of evidence as case reports (level IV), below metaanalyses, prospective randomized controlled trials, and systematic reviews. A large part of the reason that retrospective studies are weak by scientific standards is that they lack a plan to provide uniformity in the way study groups are treated and control or eliminate extraneous variables. This study was retrospective but it was not wholly without uniformity and control of variables. The reason for this was twofold, first, a single anesthetist performed all the anesthetics. Second, this anesthetist conducted the anesthetics according to two different protocols (two groups, if you will) developed for the specific surgical procedure. Essentially, the only anesthetic factor that changed between the two groups was the inclusion of dexmedetomidine in one group and not the other. In that regard, this retrospective study more closely approached a prospective design. Of course, the study still lacked randomization and comprehensive control of confounding variables, but it was certainly a notably stronger design than most retrospective studies. I am inclined to give it almost as much weight as a small prospective, randomized, controlled trial.


Michael Fiedler, PhD, CRNA



© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 2, February 28, 2009