Jonathan L. Benumof

practice Guidelines for Management of the Difficult airway An Updated Report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway

RACTICE Guidelines are systematically developed recommendations that assist the practitioner and patient in making decisions about health care. These recommendations may be adopted, modified, or rejected according to clinical needs and constraints and are not intended to replace local institutional policies. In addition, Practice Guidelines developed by the American Society of Anesthesiologists (ASA) are not intended as standards or absolute requirements, and their use cannot guarantee any specific outcome. Practice Guidelines are subject to revision as warranted by the evolution of medical knowledge, technology, and practice. They provide basic recommendations that are supported by a synthesis and analysis of the current literature, expert and practitioner opinion, open-forum commentary, and clinical feasibility data. This document updates the “Practice Guidelines for Management of the Difficult Airway: An Updated Report by

Critical Hemoglobin Desaturation Will Occur before Return to an Unparalyzed State following 1 mg/kg Intravenous Succinylcholine

Critical Hemoglobin Desaturation Will Occur before Return to an Unparalyzed State following 1 mg/kg Intravenous Succinylcholine Jonathan Benumof;Rachel Dagg;Reuben Benumof; Anesthesiology

The importance of transtracheal jet ventilation in the management of the difficult airway

The Importance of Transtracheal Jet Ventilation in the Management of the Difficult Airway Jonathan Benumof;Mark Scheller; Anesthesiology

Margin of safety in positioning modern double-lumen endotracheal tubes.

The authors have defined the margin of safety in positioning a double-lumen tube as the length of trachcobronchial tree over which it may be moved or positioned without obstructing a conducting airway. The purpose of this study was to measure the margin of safety in positioning three modern double-lumen tubes (Mallinkrodt [Broncho-Cath®], Rusch [Endobronchial tubes], and Sheridan [Broncho-Trach®]). The margin of safety in positioning a: 1) left-sided double-lumen tube (all manufacturers) is the length of the left mainstem bronchus minus the length from the proximal margin of the left cuff to left lumen tip; 2) Mallinkrodt right-sided double-lumen tube is the length of the right mainstem bronchus minus the length of the right cuff; and 3) Rusch right-sided double-lumen tube is the length of the right upper lobe ventilation slot minus the diameter of the right upper lobe. The length of the right and left mainstem bronchi were measured by in vivo fiberoptic bronchoscopy (n = 69), in fresh cadavers (n = 42), and in lung casts (n = 55), and the diameter of the right upper lobe bronchus was measured in lung casts (n = 55). The average ± SD male left and right mainstem bronchial lengths were ± 8 and 19 ± 6 mm, respectively, the average ± SD female left and right mainstem bronchial lengths were 44 ± 7 and 15 ± 5 mm, respectively, the average right upper lobe bronchial diameter was 11 mm, the proximal left cuff to left lumen tip distance was 30 mm, the length of the Mallinkrodt right cuff was 10 mm, and the length of the Rusch right upper lobe ventilation slot was 15 mm. The average margin of safety in positioning left-sided double-lumen tubes ranged 16–19 mm for the different manufacturers. The average margin of safety in positioning Mallinkrodt right-sided double-lumen tubes was 8 mm, and the margin of safety in positioning Rusch right-sided double-lumen tubes ranged 1–4 mm, depending on French size. The authors concluded that left-sided double-lumen tubes are much preferable to right-sided double-lumen tubes because they have a much greater positioning margin of safety, and that proper confirmation of proper position of either a left- or right-sided double-lumen tube should be aided by fiberoptic bronchoscopy, because the absolute distances that constitute the margin of safety are extremely small.

Obstructive sleep apnea in the adult obese patient: implications for airway management

Adult obese patients with suspected or sleep test confirmed OSA present a formidable challenge throughout the perioperative period. Life-threatening problems can arise with respect to tracheal intubation, tracheal extubation, and providing satisfactory postoperative analgesia. Tracheal intubation and extubation decisions in obese patients with either a presumptive and/or sleep study diagnosis of OSA must be made within the context that there may be excess pharyngeal tissue that cannot be visualized by routine examination, and the literature indicates an increased risk of intubation difficulty. Regional anesthesia for postoperative pain control is desirable (although such management is not necessary or possible for many of these patients). If opioids are used for the extubated postoperative patient, then one must keep in mind an increased risk of pharyngeal collapse and consider the need for continuous visual and electronic monitoring. The exact management of each sleep apnea patient with regard to intubation, extubation, and pain control requires judgment and is a function of many anesthesia, medical, and surgical considerations.

Paraplegia following intracord injection during attempted epidural anesthesia under general anesthesia.

Background and Objectives. A case of permanent paraplegia is reported following attempted epidural anesthesia for a total knee replacement in a 62‐year‐old woman with a history of lumbar laminectomy for a prolapsed intervertebral disc. Methods. Epidural puncture was attempted during general anesthesia and neuromuscular block. Results. After four unsuccessful attempts, an epidural catheter was inserted above the upper end of the laminectomy scar. Several episodes of arterial hypotension occurred intraoperative and postoperative. Operative blood loss was minimal, and no bone glue was used. The patient awoke paraparetic with a sensory level of anesthesia to T5 bilaterally. MRI revealed an air bubble in the cord at T10 and a region of increased T2‐weighted signal in the anterior aspect of the spinal cord between T4 and T5, consistent with infarction. Conclusion. Standards of management are discussed in relation to this case.

Comparison of Conventional Surgical versus Seldinger Technique Emergency Cricothyrotomy Performed by Inexperienced Clinicians

Background: Cricothyrotomy is the ultimate option for a patient with a life-threatening airway problem. Methods: The authors compared the first-time performance of surgical (group 1) versus Seldinger technique (group 2) cricothyrotomy in cadavers. Intensive care unit physicians (n = 20) performed each procedure on two adult human cadavers. Methods were compared with regard to ease of use and anatomy of the neck of the cadaver. Times to location of the cricothyroid membrane, to tracheal puncture, and to the first ventilation were recorded. Each participant was allowed only one attempt per procedure. A pathologist dissected the neck of each patient and assessed correctness of position of the tube and any injury inflicted. Subjective assessment of technique and cadaver on a visual analog scale from 1 (easiest) to 5 (worst) was conducted by the performer. Results: Age, height, and weight of the cadavers were not different. Subjective assessment of both methods (2.2 in group 1 vs. 2.4 in group 2) and anatomy of the cadavers (2.2 in group 1 vs. 2.4 in group 2) showed no statistically significant difference between both groups. Tracheal placement of the tube was achieved in 70% (n = 14) in group 1 versus 60% (n = 12) in group 2 (P value not significant). Five attempts in group 2 had to be aborted because of kinking of the guide wire. Time intervals (mean ± SD) were from start to location of the cricothyroid membrane 7 ± 9 s (group 1) versus 8 ± 7 s (group 2), to tracheal puncture 46 ± 37 s (group 1) versus 30 ± 28 s (group 2), and to first ventilation 102 ± 42 s (group 1) versus 100 ± 46 s (group 2) (P value not significant). Conclusions: The two methods showed equally poor performance.

Preoxygenation Best Method for Both Efficacy and Efficiency

THE purposes of maximally preoxygenating a patient before the induction of general anesthesia and paralysis are to provide the maximum amount of time that a patient can tolerate apnea and for the anesthesia provider to solve a cannot-ventilate, cannot-intubate situation. This issue of ANESTHESIOLOGY contains an intriguing article by Baraka et al. that describes a new method of preoxygenation that may be best with regard to both efficacy and efficiency. Maximal preoxygenation is achieved when the alveolar, arterial, tissue, and venous compartments are all filled with oxygen. However, patients with a decreased capacity for oxygen loading (i.e., decreased functional residual capacity [FRC], hemoglobin concentration, alveolar ventilation, cardiac output) or an increased oxygen extraction, or both, desaturate during apnea much faster than a healthy patient. Consequently, in patients with oxygen transport limitations (who desaturate the fastest) and in any patient in whom difficulty in managing the airway is suspected (need to tolerate apnea the longest time), maximal preoxygenation is indicated. Moreover, because the development of a cannot-ventilate, cannot-intubate situation is largely unpredictable, the desirability/need to maximally preoxygenate is theoretically present for all patients. Along this line of thought, the American Society of Anesthesiologists Difficult Airway Algorithm, which makes no mention of preoxygenation, should include a requirement for preoxygenation before the induction of general anesthesia whenever possible; obvious exclusion examples are very uncooperative adult patients and pediatric patients. Two major but preventable reasons why a patient will not be maximally preoxygenated are failure to achieve an alveolar fraction of oxygen (FAO2) 5 0.87 (i.e., failure to breathe fraction inspired oxygen tension [FIO2] 5 1.0 through a sealed system) and insufficient time of preoxygenation. The major reason for failure to achieve an FIO2 5 1.0 and an FAO2 5 0.87 is a leak under the mask, allowing inspiratory entrainment of room air. Avoiding a leak between the mask and the face is the most important factor in obtaining maximal preoxygenation because it is the one factor that cannot be compensated for by an increased duration of preoxygenation, and relatively minor degrees of leak may be hard to appreciate. Using the model of Farmery and Roe, it can be shown that when preapnea FAO2 is progressively decreased from 0.87 to 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, and 0.13 (breathing room air) for a healthy 70-kg patient, apnea times to arterial saturation of oxygen (SaO2) 5 60% are progressively decreased from 9.90 to 9.32, 8.38, 7.30, 6.37, 5.40, 4.40, 3.55 and 2.80 min, respectively. Clinical endpoints that indicate a sealed system are movement of the reservoir bag in and out with each inhalation and exhalation, respectively; presence of a normal capnogram and an end-tidal partial pressure of carbon dioxide (PETCO2) and tidal oximetry indicating appropriate inspired and end-tidal values. The half-time for exponential change in FAO2 with a step change in FIO2 is given by 0.693 3 VFRC/V̇A for a nonrebreathing system. With VFRC equal to 2.5 l, the halftime is 26 and 13 s when V̇A 5 4.0 and 8.0 l/min, respectively. Thus, most of the oxygen that can be stored in the alveolar and arterial spaces can be brought in by hyperventilation FIO2 5 1.0 for a short period of time and is the basis for the 4-deep-breath-within-30seconds method of preoxygenation (termed the “4DB/30 sec method”). Indeed, three studies have shown that there is no significant difference between the arterial oxygen tension (PaO2) achieved with 3–5 min of normal tidal volume ventilation of FIO2 5 1.0 method of preoxygenation (termed the “traditional” [T] method) compared to the 4DB/30 sec method (table 1). The similarity in PaO2 between the T and 4DB/30 sec methods of preoxygenation has led to the conclusion that the 4DB/30 sec method provides the same amount of preoxygenation as This Editorial View accompanies the following article: Baraka AS, Taha SK, Aouad MT, El-Khatib MF, Kawkabani N: Preoxygenation: Comparison of maximal breathing and tidal volume breathing techniques. ANESTHESIOLOGY 1999; 91:612–6. r

Hemodynamics of increased intra-abdominal pressure: Interaction with hypovolemia and halothane anesthesia.

The hemodynamic interaction of acute hypovolemia and halothane anesthesia in dogs with increased intra-abdominal pressure caused by intraperitoneal instillation of N2, N2O and CO2 was studied. During normovolemia and just basal pentobarbital anesthesia, the response to increase of intra-abdominal pressure to 40 torr consisted of a 35 per cent decrease in cardiac output, which was equal to the decrease in magnitude of inferior vena caval blood flow. During basal pentobarbital anesthesia, the addition of halothane anesthesia (1 MAC) in combination with hypovolemia (15 per cent blood volume loss) depressed the pre-inflation cardiac output more than addition of halothane anesthesia alone or induction of hypovolemia alone. During each of these conditions, superimposition of increased intra-abdominal pressure to 40 torr caused a further 26-43 per cent decrease in cardiac output compared with the pre-inflation value. Therefore, the greatest cardiovascular depression occurred when the animals were both hypovolemic and anesthetized with halothane. There was no difference in the responses to increased intra-abdominal pressure with the different inflating gases at any time. These findings indicate that in the presence of halothane anesthesia or hypovolemia, induction of pneumoperitoneum may cause severe cardiovascular depression.

What Is the Best Way to Determine Oropharyngeal Classification and Mandihular Space Length to Predict Difficult Laryngoscopy

BackgroundPrevious studies have suggested that the degree of visibility of oropharyngeal structures (OP class) and nun-dibular space (MS) length can predict difficult laryngoscopy. However, those studies were either inconsistent or omit description of how to perform these tests with regard to body, head and tongue position, and the use of phonation, hyoid versus thyroid cartilage and inside versus outside of the mentum. The purpose of this investigation was to determine which method of testing best predicts difficult laryngoscopy. MethodsIn each of 213 consenting adults the OP class was determined in 24 method combinations: two body positions (sitting and supine), three head positions (neutral, sniff, and full extension), two tongue positions (in and out), and with and without phonation. In each patient MS length was measured in 24 method combinations: two body positions (sitting and supine), three head positions (neutral, sniff, and full extension), two distal end points (hyoid and thyroid cartilage), and two proximal end points (Inside and outside of the men-turn). In each patient the laryngoscopic grade was determined at the time of induction of anesthesia. We denned laryngoscopic grades III (n = 24) and 4 (n = 0) as difficult. The area under the receiver operating characteristic curve (ROC area) for each combination was used to compare the combinations and determine significant differences: ROC area = 0.5 implied a totally uninformative combination and ROC area = 1.0 a combination that predicted perfectly. Logistic regression analysis was used to calculate a predictor of difficult intubation that combined both OP class and MS length (the performance index). The performance index could then be used to calculate sensitivity, specificity, positive and negative predictive value, and probability of difficult intubation. ResultsThe ROC areas for the different combinations used to assess OP class ranged from 0.78 to 0.94. The best combination was with the patient sitting, head in extension, tongue out, and with or without phonation. For MS length, the ROC areas ranged from 0.58 to 0.77; the best combination was the patient sitting, with the head in extension, with distance measured from the inside of the mentum to the thyroid cartilage. Combining the OP class and MS length (Performance Index = 2.5 × OP class – MS length in centimeters) significantly increased predictability of difficult intubation. At performance Index = 0 and = 2, the probability of difficult intubation was 3.5% and 24%, respectively. With clinically relevant outpoints for the performance index it was found that most difficult intubations could be predicted, but approximately half of those predicted to be difficult would in fact be easy. ConclusionsBased on the above ROC areas and ease of performing the test for the patient, we recommend that these tests be performed with patients in the sitting position, with the head in full extension, the tongue out, and with phonation, and with distance measured from the thyroid cartilage to inside of the mentum. Nevertheless, it is clear that these two tests, either used alone or in combination, will fail to predict a few difficult laryngoscopies and that they will predict difficult laryngoscopy in a significant number of patients in whom the trachea is easy to intubate.