ISSN NUMBER: 1938-7172
Issue 6.7 VOLUME 6 | NUMBER 7

Editor:
Michael A. Fiedler, PhD, CRNA

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

Assistant Editor
Jessica Floyd, BS

A Publication of Lifelong Learning, LLC © Copyright 2012

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

Table of Contents

EDITORIAL
  Patient Safety – How is Anesthesia Doing?
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PATIENT SAFETY
Missed Steps in the Preanesthetic Set-Up
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An assessment of the accuracy of pulse oximeters
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Parents’ understanding of and compliance with fasting instruction for pediatric day case surgery
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Emergency extracorporeal membrane oxygenation to treat massive aspiration during anaesthesia induction. A case report
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Haemodynamics and cerebral oxygenation during arthroscopic shoulder surgery in beach chair position under general anaesthesia
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Ventilation with lower tidal volumes as compared with conventional tidal volumes for patients without acute lung injury: a preventive randomized controlled trial
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Difficult Airway Society Guidelines for the management of tracheal extubation
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Intraoperative acceleromyography monitoring reduces symptoms of muscle weakness and improves quality of recovery in the early postoperative period
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Editorial
Patient Safety – How is Anesthesia Doing?

“Patient safety” has become an often-touted principle of health care practice since the original Institute of Medicine’s 1999 Report, “To Err is Human.” The focus in this report was preventable medical error. Because a reduction in medical error should be associated with an increase in patient safety, the IOM has been quite successful in raising expectations of safety among both providers and consumers.

 

According to the IOM, “errors are caused by faulty systems, processes, and conditions that lead people to make mistakes or fail to prevent them.” The health care environment should be designed so that it is harder for people to make mistakes. Anesthesia safety practices have been touted as some of the most well developed in health care. Yet, high standards are meaningless when they are not followed! Four of the articles in this issue illustrate this category: failure to complete the pre-anesthesia checklist, using inaccurate equipment for collecting crucial data, lack of adherence to nil per os guidelines, and inadequate evaluation and preparation for a typical emergency induction. Mishaps in these areas are rare and providers may become complacent about the importance of these very basic safety rules.

 

I also propose that not all “error” is the result of a mistake. An “error” may be the selection of a less favorable anesthetic agent or a less effective monitoring technique. The onus is on the anesthetist to follow the literature and look for patterns of change in anesthesia practice. Adapting a long-successful practice to new information is difficult; human behavior is relatively slow to change. There are times when evidence is so overwhelming that change is in order. I believe that the evidence for ventilation with lower tidal volumes and upgrading neuromuscular monitoring procedures clearly qualify for global application in practice. Sometimes new evidence warrants further evaluation; these are cases in which altering your practice might both benefit the patient and prevent patient harm. I would place the research on cerebral oxygenation during beach chair position and the new extubation guidelines for the difficult airway patient in this category.

 

In my view, patient safety is not just about avoiding errors of omission or commission. It is also about selecting the safest, least detrimental, and appropriate anesthetic agents and techniques.

Penelope S Benedik, PhD, CRNA, RRT


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 7, July 31, 2012




Patient Safety
Missed Steps in the Preanesthetic Set-Up

Anesth Analg 2011;113:84-8

Demaria S, Blasius K, Neustein SM


Abstract

Purpose This study was designed to identify the frequency of missed steps in the preanesthesia checklist and to identify what factors, if any, contributed to missing steps in the checklist.

 

Background Failure to complete the basic preanesthesia checklist is a well-documented threat to patient safety. Many trainees use the acronym “MS. MAID” as a memory aid to quickly ascertain room readiness prior to an anesthestic. MS. MAID calls up the following areas of anesthetic preparation:

  • machine
  • suction
  • monitors
  • airway
  • intravenous line
  • drugs

Along with this very basic list, key preparation also includes the easy access and availability of both emergency drugs and advanced airway devices. Lack of preparation in these areas may contribute to unnecessarily urgent scenarios during anesthesia induction.

 

Methodology In this prospective study, 40 operating rooms were randomly selected from within a large academic department and were surveilled five times over the course of six months. Obstetric and off-site anesthetizing locations were excluded. Unannounced surveillance occurred for both the first case of the day (AM case) and a case after 12 noon (PM case). The anesthesia provider (attending, resident physician, or CRNA) was blinded to the specific purpose of the surveyor. A Delphi approach was used to create the list of items needed for a proper set-up which included the items below:

  • Device for manual ventilation
  • Full machine checkout completed
  • Adequate suction available
  • Emergency airway devices (both endotracheal tube and laryngeal mask airway, at least 1 working laryngoscope)
  • Emergency drugs available (succinylcholine and either ephedrine or phenylephrine drawn up in labeled syringe)
  • A working intravenous line
  • Standard monitors

A “misstep” was counted if any of the above items were absent, incomplete, or nonfunctional. Workstation log (AM) and provider interview (PM) was used to determine whether the anesthesia machine was checked. Additionally, a working IV and full anesthesia monitors had to be in place and recorded prior to anesthesia induction. If the surveyor observed a missed step, it was first recorded and then corrected so that no potential harm could occur. For the purpose of statistical analysis, only 1 misstep was recorded for each data point. Multiple missteps within a single data collection were reported as observational data.

 

Data collected on the potential contributing factors to missteps included the time of day, number of cases in the surveilled operating room, experience of provider, type of case, anesthetic plan, scheduled v. unscheduled case, patient age, ASA status, and gender of patient.

 

Result Twenty-three (23) missteps occurred within the 200 data points collected (missed step rate 11.5%). In 12 cases, a manual self-inflating resuscitation bag was not available. In 6 cases, working suction was not available. There were 3 cases of “double misses”: in two, both the manual bag was missing and working suction was not available; in one, the manual bag and a working laryngoscope were missing.

 

Missed steps were more likely to occur when the anesthetic plan was not general anesthesia. In 41% of regional cases and 12% of MAC cases, a missed step occurred compared with missed steps in 5% of general anesthesia cases (P=0.005).  This represented a relative risk of missed steps 5 times greater when a regional anesthetic was planned. Missed steps occurred in 20% of rooms scheduled for 5 or more cases versus 6% in rooms scheduled for 1 to 4 cases (P=0.03).  There were significant differences in the prevalence of missed steps among anesthesia provider types with the attending physician having the highest rate at 43% versus residents at 9% and CRNAs at 15% (p=0.01).

 

Conclusion Missteps in the preanesthesia checklist are errors of omission and represent a potential for patient injury. Despite the limitations of this study design, a relatively small sample size and data from only traditional operating room environment, the study identified a significant rate of missed steps. An “extended” surgical timeout or an “anesthesia timeout” performed prior to anesthesia induction has been suggested to reduce the risk of missed steps.

 

Comment

This interesting study identified a relatively high rate of missed steps by anesthesia providers at a large academic institution. Differences were cited in the missed step rate by the experience of the provider, however, the authors did not quantify “experience” (i.e. years in professional practice), they quantified by provider type; attending, resident, or CRNA). While both CRNAs and the attending physicians had high missed step rates, the sample sizes for each group were quite small (CRNAs 2 missed steps in 13 data points; attending physicians 6 missed steps in 14 data points). This could suggest that in this particular sample, the less experienced providers (residents) were more cognizant of the standard anesthesia safety steps and/or that experienced providers (CRNAs and attending physicians) are simply more cavalier. A follow-up discussion with the providers involved in each missed step could have been an illuminating addition to this research.

 

A serious limitation of the study design was the lack of data collected from non-traditional OR settings such as off-site and obstetrical locations. A growing number of anesthetics are now performed in these areas, which, in my experience, are commonly overlooked in terms of anesthesia preparation. I recall a case scheduled in the interventional cardiology lab, which houses only an anesthesia cart but no anesthesia machine. There was no “device for manual ventilation” (self-inflating manual resuscitation bag) in the anesthesia cart, nor was one found on the crash cart for that room or in the supply closet for that room. Zero for three. A triple miss in a high risk environment but for the fact that it was caught ahead of time.

 

I can recall the day the halls were buzzing with the news that the soda lime absorbers were missing on several anesthesia machines, a fact that was not discovered until after induction and the failed ability to ventilate with the anesthesia breathing bag. But the buzzing was about why the canisters went missing, not about why the machine checks had not been done! I can recall being told the infection control nurse had dictated that all laryngoscope blades must remain in their fully sealed sterile envelopes ... without acknowledging that we MUST open them to check for adequate function of both the blade and the laryngoscope handle prior to the case.

 

I want to believe that the standards of care are more likely to be met in an academic hospital by virtue of its role in educating future providers to practice safely. But I have no evidence to support this view. Clearly, no patient injury occurred during this study because the surveyor corrected any noted misstep prior to anesthesia induction. However, this is not the case in the “real world” of anesthesia in which missed steps are not discovered until the provider needs the item!

Penelope S Benedik, PhD, CRNA, RRT


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 7, July 31, 2012





An assessment of the accuracy of pulse oximeters

Anaesthesia 2012;67:396-401

Milner QJW, Mathews GR


Abstract

Purpose This study was designed to assess the prevalence of inaccurate pulse oximeters in clinical use.

 

Background Monitoring oxygenation with pulse oximetry is a modern standard of care in anesthesia and other critical areas. Most medical instrumentation designed to measure human laboratory values is subject to strict quality control procedures. Instrument function is assessed on a daily basis by measurement of control values which must fall within rigorous and narrow limits across an appropriate range of measurement. These processes are applied to blood gas analyzers, “stat” labs, and so on. Yet no such quality control is applied to pulse oximetry, whose data are continuous and upon whose results clinical decisions and altered therapy may result. Clinicians rely upon a continued reliability of light wavelength (660 and 940 nanometers) from the light emitting diodes (LEDs) of pulse oximeters, however, once placed in use, these instruments are not normally recalibrated or assessed beyond an electrical safety check.

 

Methodology A total of 847 pulse oximeters in 29 hospitals were evaluated. A portable microspectrometer was used to measure the light wavelengths of the LEDs in the pulse oximeter sensors. The spectrometer then compared the values that were observed with expected values at SpO2s of 97%, 90%, 80% and 70%. Sensors from 17 different manufacturers were studied with 88.5% of the sensors coming from 5 manufacturers. Both new and used sensors were tested.

 

Result Functional errors in electrical circuitry that could result in inaccurate measurement were identified in 10.5% of sensors (N=89). These sensors were not tested further. Of the remaining sensors, 22% were emitting light wavelengths different from manufacturer specifications resulting in a >4% SpO2 error in the range from 70% to 100% SpO2 measurement. This resulted in actual SpO2 errors from −11% to +15% of actual SpO2 values. A total of 30% of sensors were not working according to manufacturer’s specifications. Across the range of physiologic saturation values (SpO2 80 to 100%), only 9% of sensors had error rates < 4%. No hospital studied had any reliable system for evaluating the accuracy of pulse oximeters.

 

Conclusion Significant bias was found in almost one-third of pulse oximeter sensors in clinical use with bias increasing at SpO2 90% or below. This finding does not support the general manufacturer’s attestation that accuracy for pulse oximetry is ± 2% to 3% across a range of 70% to 100%.  Mechanical, electrical, and emission spectra errors were found in this study. Clinically used pulse oximeters should undergo both routine calibration and accuracy assessment as part of their routine use.

 

Comment

It is appalling to find that instruments that anesthetists rely upon for every case potentially exhibit this very large degree of inaccuracy (−11% to +15% of actual value). The bias at SpO2 97% was narrower, −5% to +5% of actual value, but widened as the SpO2 dropped to 90% (−6% to +8% of actual value). So potentially if the pulse oximeter reads 90%, the actual saturation could be as low as 82% or as high as 96%. Even though only a small number of instruments exhibited this degree of bias, these readings would significantly change our response to the clinical scenario. Anesthesia managers need to consider arranging for a formal evaluation of pulse oximeters in the perioperative area. If this study is generalizable, this should be considered an urgent step.

Penelope S Benedik, PhD, CRNA, RRT


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 7, July 31, 2012





Parents’ understanding of and compliance with fasting instruction for pediatric day case surgery

Paediatr Anaesth 2012;22:897-900

Cantellow S, Lightfoot J, Bould H & Beringer R


Abstract

Purpose This study surveyed parents on their understanding of and adherence to fasting guidelines for their children.

 

Background Fasting non-compliance is estimated to be approximately 2% in adults and is estimated to be higher in the pediatric population. More liberal fasting guidelines may increase the risk of lack of adherence leading to possible aspiration in surgical patients. It is not clear whether parents understand and adhere to fasting guidelines for their children.

 

Methodology Parents (N=120) of elective surgical patients between 1 and 15 years were recruited to answer a two-part anonymous survey on their child’s fasting status. In the first part, parents answered the questions:

  • For how long was your child asked to fast?
  • For how long did you ensure your child was fasted for food and clear fluids?
  • What do you think is the purpose of fasting?

Parents also identified how they received fasting instructions (letter, telephone, clinic visit, etc.). In the second survey, parents completed a checklist of food or drink items they thought would be acceptable for the child to eat during a 6-hour fasting period. The item list included French fries, toast, dry cereal, sweets, gum, tea with milk and carbonated drinks.

 

Result One hundred four surveys were completed and 96% of questions were answered. A majority of parents (72%) had obtained fasting instructions from a preoperative letter. Parents reported being told to fast their children from solids for 1.5 to 24 hours (median 6 hours) and to fast liquids for 0.5 to 24 hours (median 3 hours).

 

Actual fasting times reported by parents were 3 to 40 hours for solids (median 9 hours) and 0.5 to 24 hours for liquids (median 5 hours). Fasting time from chewing gum was reported as 0 to 72 hours and from hard candy was 0 to 48 hours. Fourteen patients (13.5%) were not fasted according to current USA guidelines prior to anesthesia induction despite a preanesthetic confirmation of appropriate fasting status. European fasting guidelines were altered in 20111 so that gum chewing and hard candy is allowed up to the time of induction. Applying the new European rules, 7% of children were in violation of the fasting guidelines with 3 consuming solids within 6 hours of induction and 4 consuming liquids within 2 hours of induction.

 

The majority of parents (51%) reported they thought fasting was to prevent nausea and vomiting; only 9% thought that fasting was to prevent aspiration. When asked which items it was acceptable to consume during the fasting period, 22.1% of parents would allow toast or crackers, 17.3% would allow cereal, 14.4% would allow a sweet or gum, and 4.8% would allow French fries or a carbonated drink.

 

Conclusion    Some parents do not comply with specific fasting instructions and/or misinterpret preoperative guidelines. The non-compliance with fasting rate in this small pediatric study was 7% by European standards or 13.5% by US standards. This was from 3 to 6 times higher than the non-compliance rate for adults undergoing elective surgery. Poor recall, stress, distraction and/or lack of control of children may all have contributed to the poor compliance rate.

 

Comment

Scary, isn’t it? Even before I read this study, I had a relative lack of confidence in parental understanding of the fasting requirement and its importance. When a parent states “before midnight” in answer to “when did your child last eat or drink,” it worries me. I would prefer to hear a specific time than a rote response that mimics the preoperative instructions. I almost always follow-up with a statement about how the presence of food or drink in the child’s stomach can cause vomiting and possible aspiration of the food into the child’s lungs leading to serious illness and possibly death. That usually gets the truth out.

Penelope S Benedik, PhD, CRNA, RRT


1. Smith I, Kranke P, Murat I et al. Perioperative fasting and adult and children: guidelines from the European Society of Anaesthesiology. Eur J Anaesthesiol 2011;28:556-569.


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 7, July 31, 2012





Emergency extracorporeal membrane oxygenation to treat massive aspiration during anaesthesia induction. A case report

Acta Anaesthesiol Scand 2012;56:797-800

Wetsch WA, Spöhr FA, Hinkelbein J & Padosch SA


Abstract

Purpose This report described a case of an unexpected difficult intubation during rapid sequence induction complicated by massive aspiration of gastric contents.

 

Background A 93 kg, 5 foot 4 inch tall male was admitted with a traumatic injury to the left hand and tendon. The surgeon deemed an emergency surgery necessary. Airway evaluation consisted of a Mallampati score of II. The patient reported a history of gastroesophageal reflux disease and had “just eaten a handful of nuts.”  He refused consent for regional anesthesia, so a rapid sequence induction (RSI) was planned. Two hours after the initial anesthesia evaluation, the patient received oral sodium citrate and was positioned head elevated for an RSI. The authors stated that a gastric tube was not used because “a full stomach was not expected.” After preoxygenation with 100% oxygen, an RSI was performed, and two attempts at laryngoscopy failed. When SpO2 fell to 60%, mask ventilation was instituted; massive regurgitation occurred and a large bore suction catheter was unable to aspirate the estimated 1.5 liters of gastric content. Further attempts at laryngoscopy by the attending also failed until the oximeter no longer registered any value and the patient was severely bradycardic with dilated and unresponsive pupils. Ultimately the patient was intubated over a gum elastic bougie, saturation increased to 90% and pupillary function returned to normal.

 

Surgery was cancelled and the patient was treated for severe adult respiratory distress syndrome and aspiration pneumonia with extracorporeal membrane oxygenation (ECMO) and hypothermia.

 

Result Three weeks after these events, after a difficult course of ECMO and vasopressor support, the patient was discharged with an intact neurological status.

 

Conclusion This patient revealed after the fact that he had eaten a full meal but had not informed the anesthesia team because he was afraid that he would not get the recommended surgery.

 

Comment

Aspiration of gastric contents during anesthesia induction is a rare but devastating event. 

I would like to point out several patient safety issues in this case ... primarily because this could happen to any anesthesia provider. This patient presented with multiple risks for aspiration during anesthesia induction:

  • a traumatic injury
  • recent food ingestion
  • history of GERD
  • obesity (body mass index 35 kg/m2)

Only the Mallampati classification was reported for this patient and, as we know, a Mallampati II airway engenders relative confidence in the amount of space available in the patient’s oral cavity. Despite this, a Mallampati II is the most frequently missed intubation. Many other factors that represent an increased risk of difficult intubation are NOT reflected in the Mallampati class:

  • short or thick neck
  • full dentition
  • overbite or “buck” teeth
  • tongue size
  • inability to protrude tongue past incisors
  • high arched palate
  • temporomandibular joint problems
  • failed upper lip bite test
  • poor cervical range of motion (due to musculoskeletal issues or limited by fat pads)
  • receding chin (often masked by a beard)
  • small or stiff submental space (both thyromental distance and flexibility)
  • thyroid and laryngeal immobility (often associated with radiation to the head or neck)

There was no comment in this case about any further evaluation of the airway beyond the Mallampati class and this lack of further evaluation likely contributed to the unanticipated difficult intubation that occurred. It is an error in judgment to base an airway evaluation solely on Mallampati classification.

 

Second, “full stomach” status means that the use of gastrokinetic agents and H2-receptor blockers are acceptable preoperative interventions. These agents combined with an oral nonparticulate antacid are historically a component of the RSI technique. Especially considering that this patient waited 2 hours prior to induction, appropriate doses of metoclopramide and famotidine would have acted to reduce the gastric volume load and alter pH. An adequate onset time for these agents is not usually the case in emergency surgery scenarios. This was an opportunity lost.

 

Third, there was no evident plan for an emergency airway scenario. There was no comment that this patient refused an awake intubation although he did refuse a regional anesthetic, so an RSI with cricoid pressure was planned. It is known that cricoid pressure can distort the laryngeal aperture and increase the difficulty of intubation. That said, preparing an advanced technique that allows for cricoid pressure is an important part of a back-up plan in this scenario. An example of such an approach is found in the 2009 Journal of Clinical Anesthesia case report cited below. In this case (full stomach, emergency), after two failed attempts of direct laryngoscopy during RSI with cricoid pressure, a video-laryngoscope allowed visualization of the glottic aperture and a bougie-guided intubation was achieved while maintaining cricoid pressure and oxygenation. The presence of a bougie alone as the only backup technique is not ideal for a full stomach scenario.

Penelope S Benedik, PhD, CRNA, RRT


 

Stetson JB. Patient Safety: Prevention and prompt recognition of regurgitation and aspiration. Anesth Analg 1974;53:142-147. [Contributing Editor’s Note: A classic paper that explains the major concepts that still apply almost 40 years later.]

 

Takenaka I, Aoyama K, Kinoshita Y, Iwagaki T, Ishimura H, Takenaka Y, Kadoya T. Combination of airway scope and bougie for a full-stomach patient with difficult intubation caused by unanticipated anatomical factors and cricoid pressure. J Clin Anesth 2009;21:64-66.


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 7, July 31, 2012





Haemodynamics and cerebral oxygenation during arthroscopic shoulder surgery in beach chair position under general anaesthesia

Acta Anaesthesiol Scand 2012;56:872-879

Jeong H, Lee SH, Jang EA, Chung SS, Yoo KY


Abstract

Purpose The purpose of this study was to assess the prevalence of and risk factors for decreases in jugular venous oxygen saturation (SjvO2) in patients undergoing shoulder arthroscopy in the beach chair position. SjvO2 was also compared to concurrent cerebral oxygenation measured with near infrared spectroscopy (NIRS). The evaluation of risk factors for cerebral ischemia included patients undergoing both propofol-remifentanil and sevoflurane-nitrous oxide anesthesia.

 

Background Although rare, cerebral hypoxia with permanent brain injury has been associated with general anesthesia in the beach chair position. Near infrared spectroscopy as a measurement of regional cerebral tissue oxygenation has been suggested as an inexpensive and noninvasive monitor for cerebral perfusion in lieu of the invasive jugular venous oxygen saturation (SjvO2). While SjvO2 is considered an indirect measurement of cerebral oxygenation, drainage of the cerebral hemispheres is unequal. Approximately 70% of drainage is on one side and 30% on the contralateral side, suggesting that an assessment of global oxygenation is not entirely possible. Placement of an SjvO2 catheter requires retrograde placement of an oximetry catheter into the internal jugular vein. SjvO2 values between 55% and 70% are considered normal. Near Infrared Spectroscopy has been suggested as an alternative method to evaluate adequate cerebral perfusion and regional cerebral tissue oxygenation. It has not yet been determined whether regional cerebral tissue oxygenation estimated by Near Infrared Spectroscopy technology reflects changes in SjvO2.

 

Methodology Fifty-six ASA I to III patients scheduled for elective shoulder surgery in the beach chair position were enrolled in this study. Patients with pre-existing cerebral vascular disease or orthostatic hypotension were excluded. Patients were monitored with an arterial line referenced to the external auditory canal while in the beach chair position. Near Infrared Spectroscopy cerebral oximetry monitoring was used on all patients. Data from Near Infrared Spectroscopy-generated regional cerebral tissue oxygenation values from the right and left frontal lobes were averaged to represent overall regional cerebral tissue oxygenation.

 

Patients were induced with propofol and remifentanil and intubated with rocuronium. Anesthesia was maintained with either propofol/remifentanil TIVA or sevoflurane/nitrous oxide. The selection of anesthetic technique was not randomized, but chosen by the anesthetist. All patients were mechanically ventilated with 50% oxygen. End-tidal CO2 was maintained at 35 to 41 torr. A PreSep catheter was placed in the jugular vein contralateral to the side of surgery to measure SjvO2 and placement verified by radiography. Maintenance anesthesia was titrated to BIS values between 40 and 50. Anesthesia was adjusted to maintain mean arterial blood pressure (MAP) within 20% of preinduction values. Hypotension was defined as a MAP less than 50 mm Hg and was treated with bolus of either ephedrine (8 mg) or phenylephrine (0.1 mg) and 100 to 200 mL of IV solution. Bradycardia was defined as a heart rate less than 50 bpm and was treated with atropine (0.5 mg).

 

After hemodynamic stability was ensured, patients were positioned with the head of bed raised to 65 to 75 degrees above horizontal. Baseline data for MAP, heart rate, BIS, and regional cerebral tissue oxygenation were initially recorded on room air; these values and SjvO2 were recorded after induction and every minute after beach chair positioning for 15 minutes, then every 5 minutes for 15 minutes. The times of minimum values for regional cerebral tissue oxygenation and SjvO2 were noted. Jugular venous desaturation was defined as a value less than 50% for longer than 5 minutes; cerebral desaturation was defined as a greater than 20% decrease of regional cerebral tissue oxygenation for longer than 15 seconds.

 

A repeated measures analysis of variance was used to identify changes in cardiovascular data and oxygenation. The relationship between anesthetic technique and SjvO2 were assessed with multiple logistic regression. A Bland-Altman analysis was used to compare agreement between regional cerebral tissue oxygenation and SjvO2.

 

Result Two patients were excluded from the study due to technical problems (final N = 56). The mean age of subjects was 60 years; 21 subjects were male and 35 were female. Fifty-seven percent received propofol-remifentanil anesthesia and 43% received sevoflurane-nitrous oxide anesthesia.

 

Mean arterial pressure decreased after induction and hypotension worsened after beach chair positioning. Hypotension occurred in 69% of propofol-remifentanil patients versus 38% of sevoflurane-nitrous oxide patients (P = 0.02).

 

SjvO2 values decreased below baseline from the first minute to 20 minutes after beach chair positioning (P< 0.0001). After beach chair positioning, SjvO2 decreased by 22% in the propofol-remifentanil group versus 14% in the sevoflurane-nitrous oxide group (p=0.01).

 

Patients under propofol-remifentanil anesthesia had more episodes of SjvO2 desaturation (SjvO2 < 50%) than those under sevoflurane-nitrous oxide anesthesia; 56% versus 21% (P= 0.008). Patients in the propofol-remifentanil group were also more likely to develop SjvO2 desaturation <40% (P=0.036).

 

MAP < 50 mmHg was a more sensitive and specific indicator of SjvO2 <50% than was regional cerebral tissue oxygenation (see table 1). No patient in this study had signs of cognitive dysfunction or neurologic damage in the postoperative period.

 

 

TABLE 1: Detection of Jugular Venous Saturation Less than 50%

 

Sensitivity

Specificity

P value

MAP < 50 mmHg

73.9%

57.6%

0.047

SctO2 < 50%

30.4%

75.8%

0.696

 

 

Conclusion Forty-one percent of subjects exhibited jugular venous desaturation during shoulder arthroscopy in the beach chair position. SjvO2 desaturation was related to both hypotensive episodes and to propofol/remifentanil anesthesia maintenance. The pharmacodynamics of these agents provides an explanation of these results. Propofol decreases cerebral blood flow more than it decreases cerebral metabolism, while sevoflurane increases cerebral blood flow in excess of cerebral metabolism. There was poor agreement between regional cerebral tissue oxygenation and SjvO2 suggesting that the Near Infrared Spectroscopy technique may not adequately reflect cerebral oxygenation.

 

Comment

Cerebral hypoperfusion was the topic of heated discussion in several Anesthesia Patient Safety Foundation (APSF) Newsletters in 2009. The Spring issue contained articles on the use of Near Infrared Spectroscopy for non-cardiac surgery and BIS for detecting cerebral hypoperfusion. Later that year, recommendations from a special APSF workshop dedicated to cerebral perfusion concluded that “blood pressure in the beach chair position should be adjusted to account for a hydrostatic gradient and that deliberate hypotension should be avoided in the beach chair position.” Additionally, most participants agreed that the reduction from baseline pressure should be less than 30% with adjustment for any hydrostatic gradient and that BP should be taken in the arm not the leg. This study showed that  cerebral MAP below 50 mmHg is clearly associated with jugular venous desaturation and therefore contributes to defects in cerebral oxygenation. For patients with hypertension, the arbitrary lower limit for MAP of 50 mmHg is well below appropriate.

 

These results might provide the impetus for the development of a “safe practice” model for general anesthesia in the beach chair position. The findings and conclusions support the consideration of potent inhaled agents instead of propofol for maintenance of anesthesia along with keeping MAP above 50 mmHg at the circle of Willis. Since arterial lines are not commonly used in elective shoulder arthroscopy cases, providers have several options for effective BP monitoring. First, know and use the correction factor for the difference in height between the BP cuff and the external auditory meatus (BP decreases 2 mmHg for every 2.5 cm height above the point of measurement). Second, consider placement of an arterial line and reference it to the external auditory meatus. Third, consider carefully the choice of anesthetic agent and cerebral monitors. Although BIS was discussed as a possible tool to identify cerebral deoxygenation in 2009, in this study, BIS levels were reportedly kept between 40 and 50 even while SjvO2 was low. If BIS values dropped during hypotensive episodes, it was not reported.

 

Despite evidence of cerebral desaturation in 41% of subjects, the authors reported that “no discernable signs [of cognitive decline] ... were found.” However, no actual evaluation of cognitive function was done, making this statement an inaccurate and inappropriate conclusion. Subtle changes in cognition require specific testing with instruments that are widely available and evaluate functions such as episodic memory, executive function, and processing speed. Only when such tests are performed could this statement be supported.

Penelope S Benedik, PhD, CRNA, RRT


Jeong H, Jeong S, Lim HJ, Lee J, Yoo KY. Cerebral oxygen saturation measured by near-infrared spectroscopy and jugular venous bulb oxygen saturation during arthroscopic shoulder surgery in beach chair position under sevoflurane-nitrous oxide or propofol-remifentanil anesthesia. Anesthesiology. 2012;116:1047-56.

Schell RM, Colel DJ. Cerebral monitoring: jugular venous oximetry. Anesth Analg 2000;90:559-66. 


Editor’s Note: For more information on procedures in the beach chair position and cerebral blood pressure see “Cerebral ischemia during shoulder surgery in the upright position: a case series” in Anesthesia Abstracts Volume 4 Number 1, January 31, 2010. (Original article citation J Clin Anesth 2005;17:463-469.)


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 7, July 31, 2012





Ventilation with lower tidal volumes as compared with conventional tidal volumes for patients without acute lung injury: a preventive randomized controlled trial

Critical Care 2010;14(1);R1 Published online 2010 January 7. doi: 10.1186/cc8230

Determann RM, Royakkers A, Wolthuis EK, Vlaar AP, Choi G, Paulus F, Hofstra JJ, de Graaff MJ, Korevaar JC, Schultz MJ


Abstract

Purpose This randomized controlled trial sought to discover whether lower tidal volume ventilation compared to conventional ventilation altered cytokine production in the lungs and plasma of critically ill patients without previous acute lung injury. The authors also investigated the development of acute lung injury, duration of mechanical ventilation, and overall mortality.

 

Background Many previous studies have demonstrated the value of lower tidal volume ventilation in patients with acute lung injury or adult respiratory distress syndrome (ARDS). In these patients, a significantly lower morbidity and mortality is associated with a tidal volume of 6 mL/kg of predicted body weight instead of the “conventional” 10 mL/kg predicted body weight. Pneumonia, aspiration, multiple blood transfusions, trauma, and shock, comorbidities that occasionally present to the OR, not only worsen but also may instigate lung injury. Large volume ventilation has been associated with the production of cytokines and other inflammatory mediators suggesting that acute lung injury in previously healthy lungs may be a largely preventable disease.

 

Methodology One hundred fifty patients without preexisting lung injury who required mechanical ventilation for more than 72 hours were enrolled. Patients with previous lung surgery were excluded. Patients were randomized into conventional volume ventilation of 10 mL/kg predicted body weight or small tidal volume (VT) ventilation of 6 mL/kg predicted body weight. If patients randomized to the small VT group became severely dyspneic, tachypneic, or uncomfortable, VT could be increased to 7 to 8 mL/kg predicted body weight at the discretion of the attending physician. The fraction of inspired oxygen and positive end-expiratory pressure were set based on the patient’s PaO2 and according to the ICU’s local protocol. All patients were tested for tolerance to pressure support ventilation three times daily; if tolerated, pressure support was used to achieve target tidal volume. Patients were weaned from pressure support with a standard protocol and extubated based on typical criteria. If the patient required reintubation within 28 days, they were placed in the same group to which originally randomized. The presence of lung injury was defined by consensus criteria: acute onset of bilateral chest X-ray infiltrates and PaO2 to fraction of inspired oxygen ratio < 300 mm Hg.

 

Demographic data and ventilatory parameters including the oxygenation index and lung injury score were collected at baseline and throughout the study. On entry to the study and every second day, bronchoalveolar lavage was performed to determine levels of tumor necrosis factor α, interleukin-1β and interleukin-6. Concurrently, arterial blood was drawn for interleukin-6 measurement.

 

A sample size of 200 was determined from power analysis. Physicians blinded to clinical parameters and randomization scored chest radiographs and reviewed the oxygenation ratio, echocardiography data, pulmonary capillary wedge pressures, and fluid balance to determine the development of acute lung injury or adult respiratory distress syndrome (ARDS). Any patient who developed lung injury was subsequently ventilated at 6 mL/kg predicted body weight but was kept in their original group for analysis.

 

Result Patients in the low VT group were slightly older (63 versus 58 years, P = 0.06) and a higher proportion were current smokers (76% versus 61%, P=0.04). Otherwise no significant differences were found between groups.

 

The study was terminated after accruing 150 subjects because 13.5% (10 of 74) of patients in the conventional ventilation group developed acute lung injury or ARDS compared with only 2.6% (2 of 76) in the low VT group (P = 0.01). The relative risk of developing acute lung injury in the conventional group was 5 times greater than in the low VT group.

 

The twelve patients who developed lung injury met the criteria at 2 ± 1 days. After 7 and 28 days, there were no differences between groups in the number of ventilator-free days or mortality. There were no differences in the number of days that sedation or vasopressors were required between groups. Both tidal volume and PEEP level were independent predictors of the development of lung injury. The interleukin-6 level in lung fluid was significantly higher in the conventional VT group (P = 0.04), but no differences were found in tumor necrosis factor α and interleukin-1β.

 

Conclusion A lower tidal volume of 6 mL/kg predicted body weight may prevent the development of new lung injury if instituted at the onset of mechanical ventilation.

 

Comment

This 2010 critical care study is relevant to anesthesia practice. How? Because a subset of surgical patients is at risk for the development of ventilator-associated lung injury. This is more likely in trauma victims and other critically ill patients who present without acute lung injury. In the interest of injury prevention, anesthesia providers should consider taking a long-term view when selecting ventilator settings for these patients. This means making the simple calculation of predicted body weight and setting the tidal volume to 6 mL/kg predicted body weight and not more than 8 mL/kg predicted body weight. A recent review of current practice (see Jaber et al. referenced below) reveals that female sex and being overweight or obese significantly increases the chance of being ventilated with a tidal volume > 10 mL/kg predicted body weight. Clearly, this single choice could significantly affect an individual’s outcome.

Penelope S Benedik, PhD, CRNA, RRT


Beck-Schimmer B, Schimmer RC. Perioperative tidal volume and intra-operative open lung strategy in healthy lungs: where are we going? Best Pract Res Clin Anaesthesiol. 2010;24:199-210.

Jaber S, Coisel Y, Chanques, G. et al. A multicentre observational study of intra-operative ventilatory management during general anaesthesia: tidal volumes and relation to body weight. Anaesthesia 2012;67:999-1008.


Contributing Editor’s Note: The simplest formula for a quick and easy calculation of predicted body weight is height in meters squared times 22 (PBW = 22 × m2).


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 7, July 31, 2012





Difficult Airway Society Guidelines for the management of tracheal extubation

Anaesthesia 2012;67:318-340

Popat M, Mitchell V, Dravid R, Patel A, Swampillai C, Higgs A


Abstract

Purpose The aim of this paper was to suggest physiologically sound principles for guiding extubation practices in patients who have a difficult airway.

 

Background Planning intubation for patients with known or suspected difficult airway has been well described and forms an important part of anesthesia practice. On the other hand, no clear advice beyond “extubate awake” has been offered to help providers create optimal extubation conditions. The authors rightly point out that airway conditions around extubation are substantially different than conditions during a carefully controlled and planned intubation. Edema from intubation trauma, surgery, or positioning can compromise a previously intact tissue bed. Emergence from anesthesia is less controlled and may be prolonged by residual anesthetics contributing to airway compromise. Additionally, perioperative staff generally understand delay related to intubation, but are not as forgiving about “delay” around the extubation process.

 

Methodology Despite a review of the literature from 1970 to 2008, no randomized controlled trials or meta-analyses were identified on extubation complications and practice. These guidelines were based on expert opinion from editorials, textbooks, and solicited comments. The Difficult Airway Society (DAS) work group formed proposed guidelines and circulated the drafts to DAS members and international experts.

 

Result Potential issues during tracheal extubation were categorized as:

  1. problems related to airway reflexes (exaggerated, diminished, or dysfunctional)
  2. depletion of oxygen stores
  3. airway injury
  4. physiological system compromise
  5. human factors

 

A key principle is that extubation is elective and should be planned and performed with care. The extubation guidelines describe how to plan, prepare for, and perform a safe extubation after difficult intubation and how to provide appropriate post-extubation care. DAS extubation planning is based on both airway risk factors and general risk factors; described in three algorithms.

 

The basic algorithm reviews both general and airway risk factors for a difficult extubation in which the patient is stratified to either a “low-risk” or “at-risk” category. Low-risk patients include fasted patients with an uncomplicated airway and no significant comorbidities. At-risk patients include those in whom the ability to oxygenate is questionable, reintubation is potentially difficult, and/or significant comorbidities are present. In all cases, the airway should be assessed for any changes that have occurred since the intubation (distortion, edema, bleeding, etc.).

 

Both “low-risk” and “at-risk” algorithms were developed that include detailed sequences for each. For a low-risk case, procedures are described for both an awake and a deep extubation. For awake extubation, patients should be:

  • preoxygenated
  • suctioned under direct vision
  • positioned head-up or left lateral if empty stomach (especially in the obese)
  • positioned head down if full stomach
  • muscle relaxant reversed
  • have an appropriate bite block in place (not an oral airway)

Deep extubation is an advanced technique requiring experience and the full attention of the anesthetist until the patient is fully awake in the operating room. Additionally, deep extubation should only be performed in a patient with no risk of aspiration and in whom reintubation would be easy.

 

The algorithm for at-risk extubation also includes careful evaluation and planning. The most important step in the at-risk extubation plan is answering the question “is it safe to remove the tube?” If not, either extubation should be postponed or a more permanent airway be used (e.g. tracheostomy). If extubation is deemed safe, two pathways are defined: awake extubation and advanced techniques. The appropriate use of advanced techniques including LMA-exchange, remifentanil infusion, or the use of an airway exchange catheter are described in detail. The guidelines note that advanced techniques require training and experience and should not be attempted by junior anesthetists or trainees.

 

Post-extubation care and follow-up are an important part of anesthesia. The guidelines review appropriate staffing, observation and identifying warning signs, availability of the difficult airway cart, safe transfer procedures, respiratory care, and documentation of clinical details and the recovery plan.

 

Conclusion A thoughtful plan for extubation should be a required component of every anesthetic and may be more important than the intubation plan. By the time of extubation, airway conditions are generally much worse than during intubation.

 

Comment

Guidelines are generally the most helpful in critical but rare situations; here is a sorely needed guideline to support a crucial part of an anesthetic—the END! The vast majority of extubations occur in low risk, fasted, easy to intubate patients. These guidelines help us plan and prepare for extubating at risk patients who have difficult airways that are more compromised for extubation than for intubation. They also provide support for a decision to delay extubation if the conditions are not deemed to be safe. Some caveats have already been pointed out about these guidelines (see reference below). First, some of the recommended techniques will require further education and training because anesthetists may not be familiar with them. LMA exchange and airway exchange catheters in particular are not commonly practiced. Second, oral airways are not usually effective bite blocks and may fail if used for this purpose. Rolled gauze--taped to the endotracheal tube--should be placed between the molars; placement between the front teeth is ineffective.

Penelope S Benedik, PhD, CRNA, RRT


The August 2012 issue of the journal, Anaesthesia (volume 67, number 8) contains letters to the editor about these guidelines beginning on page 917.


Editor’s Note: The editors of Anesthesia Abstracts strongly encourage readers to examine the extubation algorithms on the difficult airway society web site. We have not included them here in observance of copyright laws.

The Difficult Airway Society Guidelines for the management of tracheal extubation can be accessed at

http://www.das.uk.com/content/das-extubation-guidelines.


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 7, July 31, 2012





Intraoperative acceleromyography monitoring reduces symptoms of muscle weakness and improves quality of recovery in the early postoperative period

Anesthesiology 2011;115:946-954

Murphy GS, Szokol JW, Avram MJ, Greenberg SB, Marymont JH, Vender JS, Gray J, Landry E, Gupta DK


Abstract

Purpose This study was designed to determine whether acceleromyographic monitoring of neuromuscular function would reduce the signs and symptoms of residual paralysis in the recovery room compared to conventional train-of-four (TOF) monitoring.

 

Background It has been clearly demonstrated that a large proportion of patients (38% to 64%) who receive intermediate-acting neuromuscular blockers during surgery have residual neuromuscular blockade in the postanesthesia recovery room even after receiving reversal agents. The updated standard defines residual blockade as present if the train-of-four ratio (TOF Ratio) is less than 0.9. This residual blockade occurs even when 4 of 4 apparently equal twitches are present by conventional peripheral nerve stimulator monitors, demonstrating the lack of sensitivity of conventional PNS monitoring. The TOF Ratio is measured by acceleromyography, a technique now available outside the research lab. A TOF Ratio between 0 and 0.9 is associated with a myriad of objective signs including airway obstruction, hypoxemia, difficulty swallowing and speaking, visual disturbances, and facial and generalized weakness. To what extent a patient feels uncomfortable with these signs and symptoms and how they affect the patient’s recovery has not yet been studied.

 

Methodology This was a randomized, double-blind study of 155 ASA class I to III patients older than 18 years who were scheduled for elective surgery at least 60 minutes in duration requiring neuromuscular paralysis. Patients who had any disease that interfered with neuromuscular function, renal disease or hepatic disease were excluded. Access to the ulnar nerve for neuromuscular monitoring was required. Prior to entering the operating room, patients were randomized to conventional TOF monitoring (TOF-PNS group) or acceleromyography monitoring (TOF-Ratio group). Both groups used the TOF-Watch peripheral nerve stimulator. The TOF-PNS group were blinded to the TOF Ratio information and had access only to visual or tactile TOF counts. The TOF Ratio group had access to the train-of-four ratio throughout the case.

 

A standardized anesthetic was provided to both groups and normothermia maintained. Intubation was facilitated with rocuronium 0.6 to 0.8 mg/kg IV. Both groups kept a visual TOF count of 2 to 3 during the case with rocuronium boluses of 5 to 10 mg given prn. No rocuronium was administered during the last 20 to 30 minutes of the case. All patients received reversal with neostigmine 50 mcg/kg when a TOF count of at least 3 occurred. In the TOF-PNS group, patients were extubated only after no fade was seen on the TOF count and clinical criteria were met (sustained head lift, stable ventilatory pattern, following commands). In the TOF Ratio group, patients were extubated only after a TOF Ratio greater than 0.8 was achieved and the same clinical criteria were met.

 

Immediately after entry into the PACU, and at 20, 40, and 60 minutes after PACU admission, the TOF Ratio was determined using a TOF-Watch PNS. Subsequent to this determination, a blinded research assistant assessed patients for objective signs of muscle weakness (11 tests of muscle strength) or patient-reported subjective symptoms of muscle paresis if the previous 11 tests were difficult or uncomfortable to perform. Patients also quantified their overall feeling of muscle weakness. Aldrete scores were taken every 10 minutes by the recovery nurses who were blinded to both the actual TOF Ratio and the group assignment. The time until the Aldrete score was ≥ 8 of 10 was achieved was noted, indicating readiness for discharge. Patients also completed a “quality of recovery” score (QoR-9), an instrument with accepted validity and reliability in patients undergoing a variety of surgical procedures.

 

Result No differences in demographics were found. No differences in duration of surgery, temperature, rocuronium total dose, or time from neostigmine administration to PACU were found. Neuromuscular recovery for each group at the time of PACU admission is shown in table 1.

 

 

 

Table 1: Neuromuscular Recovery on PACU Admission

Control Group

(TOF-PNS)

Acceleromyography

(TOF Ratio) Group

 

P Value

Mean TOF Ratio in PACU

0.88

0.98

0.004

# patients TOF Ratio < 0.9

50% (n=37)

14.5% (n=11)

<0.0001

# patients TOF Ratio < 0.7

19% (n=14)

4% (n=3)

0.004

 

 

The patient’s self-reported overall weakness score, from 0 (extreme weakness) to 10 (no weakness) is illustrated in figure 1. The two groups differed in overall weakness across all time points (P< 0.0001). This chart reflects the fact that 10 of 76 TOF Ratio patients were extubated before a TOF Ratio > 0.8 was achieved because they were not tolerating the endotracheal tube. Of these, 3 patients had TOF Ratios < 0.7 on entry to the PACU and still had not reported full recovery from overall weakness at 60 minutes.

 

 

Figure 1: Self Reported Weakness Score

Figure 1

Note: scale from 0 (extreme weakness) to 10 (no weakness).

 

The number of signs of muscle weakness had a low sensitivity of only 43% for a TOF Ratio < 0.9. In fact, the median number of signs (objective tests) of muscle weakness in both groups for all times in the PACU was zero. Subjective testing simply did not reliably gauge residual neuromuscular blockade.

 

The number of symptoms of muscle weakness had a relatively high sensitivity of 87% and a specificity of 82% for a TOF Ratio < 0.9. Figure 2 compares the median number of symptoms reported by patients on PACU admission and at 20, 40, and 60 minutes after admission. Only the acceleromyography group had no symptoms of muscle weakness at both 40 and 60 minutes post-PACU admission.

 

 

Figure 2: Median Number Symptoms of Weakness

Figure 2

Note: y axis is number of symptoms of weakness reported by patient at each time point.

 

 

By the 60 minute PACU evaluation, 36% of all subjects still reported an overall generalized weakness. The Aldrete scores did not predict muscle weakness nor were they affected by residual muscle weakness. The use of acceleromyography improved the overall quality of recovery by patient self-report but did not alter length of stay.

 

Conclusion Compared with conventional TOF monitoring, patients monitored with acceleromyography have lower incidence of residual muscle weakness and report fewer symptoms of muscle weakness during the postoperative recovery period.

 

Comment

Signs are objective measures and include testable characteristics like the ability to accomplish a 5-second head lift or 5-second tongue protrusion; have the ability to swallow, speak or cough; or the ability to breathe deeply. Symptoms are subjective measures and rate the patient’s experience of trying to perform the objective measure. So a potential sign of poor neuromuscular recovery is a tidal volume measured at 175 mL in a 70 kg patient; a symptom of the same is a patient who states, “I can’t breathe.” Thus, if a patient feels weak and uncomfortable, it is likely that they are still partially paralyzed. Absent the ability to accurately measure a TOF Ratio (you don’t have a TOF-Watch), how the patient feels seems to be a more accurate assessment of neuromuscular function than our currently used “objective” clinical tests!

Penelope S Benedik, PhD, CRNA, RRT


Contributing Editor’s Note: I purchased a TOF-Watch several years ago for use in my practice.


© Copyright 2012 Anesthesia Abstracts · Volume 6 Number 7, July 31, 2012