Simulation Technique for Difficult Intubation: Teaching Tool or New Hazard? Joel S. Goldberg, MD,* Andrew C. Bernard, EMT,? Richard J. Marks, MBBS, FFARCS (Eng.),$ Robert N. Sladen, MB, MRCP (UK), FRCP(C)# Anesthesiology Center;
ical Center,
*Assistant Medical Research Professor of Anesthesiology, Duke University Medical Center TResearch Assistant, Duke University Medical Center $Visiting Associate in Anesthesiology, Duke University Medical Center. Currently, Senior Registrar in Anesthesia, Royal Free Hospital, London, England $Associate Professor of Anesthesiology and Surgery, Duke University Medical Center; Chief, Anesthesiology Service, Durham Veterans Administration Medical Center Address reprint requests to Dr. Goldberg at the Anesthesiology Service, Durham Veterans Administration Medical Center, 508 Fulton Street, Durham, NC 27705, USA.
Service,
Durham
and Department Durham,
Veterans
of Anesthesiology,
Administration Duke
University
Medical Med-
NC.
This investigation evaluated the risks of a simulation drill designed to improve the skill of anesthesia personnel in dealing with an unexpected dafficult intubation. In a controlled prospective study, 40 patients with normal airways scheduled to undergo noncardiothoracic surgery were randomized into two groups of 20 patienki. In the control group, intubation was performed by standard techniques. In the simulation group, intubation of a difficult airway was simulated and performed with the aid of an endotracheal tube introducer. Heart rate (HR); systolic, mean, and diastolic blood pressures (BPS); and arterial oxygen saturation were measured noninvasively during the preinduction period and 1 minute postintubation. A record was kept of all adverse events, including electrocardiogram (EKG) evidence of myocardial ischemia or cardiac arrhythmias, esophageal intubation, pulmonary aspiration, or tracheal injury. There were no significant dfferences in percent changes in HR, BP, or oxygen saturation between the two groups. There were five uncomplicated esophageal intubations in the simulation group compared with none in the control group (p = 0.001). No other adverse events were recorded. The potential hazards of esophageal intubation should be considered before this simulation drill is performed. Keywords: Intubation, airway resistance.
endotracheal;
anesthesia, esophagus;
trachea;
Received for publication June 8, 1989; revised manuscript accepted for publication August 21, 1989.
Introduction
0 1990 Buttetworth
Inability to successfully intubate the trachea is a leading cause of anesthetic morbidity and mortality. l,* Loss of a patent airway, esophageal intubation,
Publishers
J. Clin. Anesth.,
vol. 2, Jan/Feb
1990
21
Original Contributions
and pulmonary aspiration of gastric contents are infrequent but devastating complications of failed endotracheal intubations. Of serious respiratory incidents defined in a review of closed malpractice claims performed by the American Society of Anesthesiologists, unrecognized esophageal intubation was the single most frequent cause of critical anesthesia-related injury.’ An international review of anesthetic mishaps clearly implicates the unexpected difficult intubation as a major cause of these anesthetic misadventures3 (Table 1).
Physical examination may fail to predict a difficult laryngeal exposure or may not be possible prior to endotracheal intubation during cardiopulmonary resuscitation. Findings on physical examination used to predict a difficult intubation include a short recessed mandible, a large tongue, a short neck, and a full set of protruding teeth. 4 These signs are not sensitive indicators, however, and the unexpected difficult intubation caused by failure to expose the glottis is a continued hazard to anesthesiologists. Improved monitoring capabilities and vigilance have reduced airway catastrophes, but these capabilities are also not without limitations. Interpretation of end-tidal CO, measurement by capnography, considered the most reliable monitor of endotracheal tube placement,5 may be falsely positive or negative. If respiratory gas has inadvertently entered the stomach prior to esophageal intubation, the initial carbon dioxide measurements will be greater than atmospheric levels.6 This situation can mislead the anesthesiologist to believe that the endotracheal tube is properly positioned. Conversely, pulmonary blood flow may be severely reduced during cardiopulmonary resuscitation, producing an end-tidal CO, that is lower than the sensitivity of the measuring device.’ In this instance, correct placement of the endotracheal tube may be mistaken for an esophageal intubation. Finally, capnography does not help prevent pulmonary
Table 1.
Grade 1
Grade 2
Grade 3
Grade 4
Figure 1. The four classes of laryngeal exposures as seen during laryngoscopy: grade 1, normal exposure of glottis;
grade 2, partial exposure of glottis; grade 3, epiglottis visualized but glottis not seen; grade 4, epiglottis not visualized.
Intubation-Related Anesthetic Catastrophe@
Author(s)
Country
Green RA, Taylor THa
U.K. Australia U.S.A.
Holland Rb Solazzi RW, Ward RJc
Claims from the Medical Protection Society. bCoroner’s records from New South Wales. l mm ST segment depression), pulmonary aspiration of gastric contents, tracheal injury, and esophageal intubation. The two-tailed t-test was used to compare the percent change in data from preinduction to postintubation between the simulation group and the control group. The intubation success of the simulation group 24
J. Clin. Anesth., vol. 2, JanlFeb
1990
compared with that of the control group was analyzed by the Fisher’s exact test.
Results There were no significant differences in age and ASA physical status between the two groups (Table 2). Percent changes in HR, BP, oxygen saturation and from preinduction to postintubation were not significantly different between the simulation group and the control group (Table 3). There were no cases of hypoxemia, myocardial ischemia, pulmonary aspiration of gastric contents, or tracheal injury. There were live esophageal intubations in the 20 patients on whom the simulation was performed, compared with no esophageal intubations in the control group (Table 4). This difference was statistically significant (p = 0.001). There was no evidence of hypoxemia, arrhythmias, myocardial ischemia, or pulmonary aspiration of gastric contents associated with the esophageal intubations. All five patients were successfully reintubated on the first attempt. On intubation, one patient in the control group showed evidence of a junctional rhythm. Also, one patient undergoing simulated intubation experienced a brief period of supraventricular tachycardia, which the supervising anesthesiologist believed to be unrelated to the simulation, since it occurred after successful endotracheal intubation. There was no evidence of myocardial ischemia or hemodynamic instability caused by the arrhythmias.
Discussion Evidence of airway injury, loss of airway control, hemodynamic instability, myocardial &hernia, and oxygen desaturation were considered as risks to patients participating in the simulation drill described by Cormack and Lehane.* The investigators were surprised to discover that five esophageal intubations ocTable 2. Age and ASA Physical Status of Subjects in the Study
Age* ASA physical status (I, II, III)+ Means 2 *p = 0.64 ‘p = 0.30
SD.
Simulation Group (II = 20)
Control Group (n = 20)
53.7 2 15.7
51.1 + 18.1
3, 10, 7
6, 8, 6
Simulationfor difficult intubation: Goldberg et al. Table 3.
Percent Change between Preintubation and Postintubation Data Simulation
Post
Pre
HR (beats/min)* SBP (mmHg)+ DBP (mmHg)* MAP (mmHg)* SaO, (%)I
77 131 80 101 99
2 ? f. r 4
Group (II = 20)
16 21 7 14 2
91 153 94 117 99
2 r 4 2 c
Control Group (n = 20) Pre
% Change
20 38 21 27 2
15 23 27 27 -0.17
* + ? 2 5
20 24 26 29 0.8
73 141 78 101 99
” I t t 2
Post 11
26 13 17 1
86 144 86 107 99
+ 18 +- 34 r 21 + 28 * 1
% Change
16 27 28 26
* ? ? +
16 28 28 24 0 ?I 0.97
Means k SD. Note: p values for comparison
of percent change between simulation group and control group.
*p = 0.87 ‘p = 0.63 ‘p = 0.82 ‘p = 0.94 ‘/I = 0.85 Pre = preinduction; Post = 1 minute postintubation; HR = heart rate; SBP = systolic blood pressure; MAP = mean arterial pressure; SaO, = arterial oxygen saturation.
Table 4.
Intubation Success Simulation Group (n = 20)
Tracheal intubation Esophageal intubation
15 5
Control Group (n = 20)
20 0
p = 0.001.
curred in the simulation group. These intubations could not be attributed to learning or to a single individual because they occurred randomly throughout the study with three different intubators. However, the 25% incidence of esophageal intubation has raised a number of questions. First, what are the ethical considerations of a simulation drill that may cause an esophageal intubation? According to Cormack and Lehane, “There is no risk to the patient and the time taken is similar to that for standard intubations” (p. 1108). The present authors strongly disagree and feel that informed consent should be obtained from all patients who participate in the simulation drill. Although none of the patients in this study suffered any injuries, the risks of hypoxemia, pulmonary aspiration, or gastric distention from recognized esophageal intubation were greater in the simulation group. Furthermore, an esophageal intubation clearly increases the time for a successful endotracheal intubation. Second, what should be the anesthetic management of an esophageal intubation? The investigators chose to remove the endotracheal tube immediately after recognition, believing that the risk of aspiration was
DBP = diastolic blood pressure;
less than the risk of hypoxemia and hypercarbia caused by leaving the tube in place and ventilating with a mask or attempting a second intubation without first ventilating the patient. Third, should patients volunteering for the simulation drill be protected from gastric acid aspiration with antacids, H, antagonists, and metaclopramide? Traditionally, these medications have been used prophylactically in high-risk or full-stomach patients. Subjecting volunteers to potential side effects that include inhibition of hepatic enzyme systems, potentiation of the actions of anticoagulants and phenytoin, and increased postoperative somnolence does not appear to be justified. Fourth, what would be the incidence of esophageal intubations in grade 3 exposures if an introducer were not used? Cormack and Lehane* have incorporated the use of the introducer as an essential part of their simulation drill. If the simulation drill can be practiced effectively without the aid of the introducer, elimination of the potential hazard of tracheal perforation would permit more widespread use of the drill, even though the current investigation showed no evidence of tracheal injury. Perhaps the introducer is not the answer to the grade 3 problem. The authors are currently evaluating the simulation drill without the aid of an endotracheal tube introducer. Fifth, was the high frequency of esophageal intubation caused by the investigators’ inability to perform the drill properly? One of the investigators learned the simulation drill during a rotation at the Northwick Park Hospital in London and taught it to the other investigators and trainees at the Durham Veterans Administration Medical Center. J. Clin. Anesth.,
vol. 2, Jan/Feb
1990
25
Orig-kuzl Contributions
Finally, and most importantly, do the possible benefits of this training outweigh the potential hazards of esophageal intubation ? The authors agree with Cormack and Lehane that it is not yet possible to prove that this drill reduces the number of failed intubations, since the rarity of this occurrence means that a study confined to one unit would take decades to collect the necessary data. Mallampati et al.” studied the hindered views of the faucial pillars, soft palate, and uvula produced by a large tongue as a clinical sign to predict difficult tracheal intubation. In 210 ASA I and II patients, they identified 9 (4.3% of the total patients) in whom the glottis could not be exposed by direct laryngoscopy. In all these patients, the uvula could not be visualized. If nonvisualization of the uvula helps to predict the grade 3 exposure, should the airway of a patient who is at high risk for pulmonary aspiration and whose uvula is obscured by the tongue be intubated while awake? With the patient anesthetized, encountering a grade 3 exposure may have a 1 in 4 chance of unsuccessful intubation. The authors believe that an esophageal intubation in a patient with a full stomach greatly increases the risk of aspiration. Careful consideration should be given to performing an awake intubation in a patient with these anesthetic problems. The investigators chose not to standardize induction techniques, muscle relaxants, or anesthesia personnel in order to demonstrate that this simulation drill may be used in a variety of clinical situations. Furthermore, they hope that this simulation can serve as a model to evaluate devices used for unexpected difficult intubations leading to scientific rather than anecdotal justification for their use. Whether the simulated grade 3 represents the same hidden anatomy and poses the same obstacles to successful intubation as that of the nonsimulated grade 3 exposure cannot be easily demonstrated and may be a limitation of this type of drill. In conclusion, failure to expose the glottis during laryngoscopy (grade 3 view) is an unpredictable complication that may be the harbinger of an airway catastrophe. The authors believe that the simulation drill
26
J. Clin. Anesth., vol. 2, Jan/Feb 1990
devised by Cormack and Lehane is an honest attempt at improving the anesthesiologist’s skill at successful intubation without glottic visualization. However, this simulation drill is associated with an unexpectedly high incidence of esophageal intubation. Although the drill has been uncomplicated thus far, the etiology and risks of esophageal intubation associated with it must be investigated further before it can be recommended for widespread use in the training of anesthetists in this country.
Acknowledgment The authors wish to thank James E. Linthicum of the Durham Veterans Administration Medical Center for medical illustrations.
References 1. Cheney FW, Posner K, Caplan RA, Ward RJ: Standard of care and anesthesia liability. JAMA 1989;26 1: 15991633.
Utting JE, Gray TC, Shelly FC: Human misadventure in anesthesia. Can Anaesth Sot J 1979;26:472-8. Pierce EC, Cooper JB, eds: Analysis of anesthetic mishaps. Int Anesthesiol Clin 1984;22:43-89. White A, Kander PL: Anatomical factors in difficult direct laryngoscopy. Br J Anaesth 1975;47:468-74. Birmingham PK, Cheney FW, Ward RJ: Esophageal intubation: a review of detection techniques. Anesth Analg 1986;65:886-91. 6. Linko K, Paloheimo M, Tammisto T.: Capnography for detection of accidental oesophageal intubation. Acta Anaesthesiol Stand 1983;27:199-202. Falk JL, Rackow EC, Weil MH: End-tidal carbon dioxide concentration during cardiopulmonary resuscitation. N Engl J Med 1988;318:607-11. Cormack RS, Lehane J: Difficult tracheal intubation in obstetrics. Anaesthesia 1984;39: 1105-l 1. Mallampati SR, Gatt SP, Gugino LD, et al: A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anuesth Sot J 1985;32:429-34.
ical Center,
*Assistant Medical Research Professor of Anesthesiology, Duke University Medical Center TResearch Assistant, Duke University Medical Center $Visiting Associate in Anesthesiology, Duke University Medical Center. Currently, Senior Registrar in Anesthesia, Royal Free Hospital, London, England $Associate Professor of Anesthesiology and Surgery, Duke University Medical Center; Chief, Anesthesiology Service, Durham Veterans Administration Medical Center Address reprint requests to Dr. Goldberg at the Anesthesiology Service, Durham Veterans Administration Medical Center, 508 Fulton Street, Durham, NC 27705, USA.
Service,
Durham
and Department Durham,
Veterans
of Anesthesiology,
Administration Duke
University
Medical Med-
NC.
This investigation evaluated the risks of a simulation drill designed to improve the skill of anesthesia personnel in dealing with an unexpected dafficult intubation. In a controlled prospective study, 40 patients with normal airways scheduled to undergo noncardiothoracic surgery were randomized into two groups of 20 patienki. In the control group, intubation was performed by standard techniques. In the simulation group, intubation of a difficult airway was simulated and performed with the aid of an endotracheal tube introducer. Heart rate (HR); systolic, mean, and diastolic blood pressures (BPS); and arterial oxygen saturation were measured noninvasively during the preinduction period and 1 minute postintubation. A record was kept of all adverse events, including electrocardiogram (EKG) evidence of myocardial ischemia or cardiac arrhythmias, esophageal intubation, pulmonary aspiration, or tracheal injury. There were no significant dfferences in percent changes in HR, BP, or oxygen saturation between the two groups. There were five uncomplicated esophageal intubations in the simulation group compared with none in the control group (p = 0.001). No other adverse events were recorded. The potential hazards of esophageal intubation should be considered before this simulation drill is performed. Keywords: Intubation, airway resistance.
endotracheal;
anesthesia, esophagus;
trachea;
Received for publication June 8, 1989; revised manuscript accepted for publication August 21, 1989.
Introduction
0 1990 Buttetworth
Inability to successfully intubate the trachea is a leading cause of anesthetic morbidity and mortality. l,* Loss of a patent airway, esophageal intubation,
Publishers
J. Clin. Anesth.,
vol. 2, Jan/Feb
1990
21
Original Contributions
and pulmonary aspiration of gastric contents are infrequent but devastating complications of failed endotracheal intubations. Of serious respiratory incidents defined in a review of closed malpractice claims performed by the American Society of Anesthesiologists, unrecognized esophageal intubation was the single most frequent cause of critical anesthesia-related injury.’ An international review of anesthetic mishaps clearly implicates the unexpected difficult intubation as a major cause of these anesthetic misadventures3 (Table 1).
Physical examination may fail to predict a difficult laryngeal exposure or may not be possible prior to endotracheal intubation during cardiopulmonary resuscitation. Findings on physical examination used to predict a difficult intubation include a short recessed mandible, a large tongue, a short neck, and a full set of protruding teeth. 4 These signs are not sensitive indicators, however, and the unexpected difficult intubation caused by failure to expose the glottis is a continued hazard to anesthesiologists. Improved monitoring capabilities and vigilance have reduced airway catastrophes, but these capabilities are also not without limitations. Interpretation of end-tidal CO, measurement by capnography, considered the most reliable monitor of endotracheal tube placement,5 may be falsely positive or negative. If respiratory gas has inadvertently entered the stomach prior to esophageal intubation, the initial carbon dioxide measurements will be greater than atmospheric levels.6 This situation can mislead the anesthesiologist to believe that the endotracheal tube is properly positioned. Conversely, pulmonary blood flow may be severely reduced during cardiopulmonary resuscitation, producing an end-tidal CO, that is lower than the sensitivity of the measuring device.’ In this instance, correct placement of the endotracheal tube may be mistaken for an esophageal intubation. Finally, capnography does not help prevent pulmonary
Table 1.
Grade 1
Grade 2
Grade 3
Grade 4
Figure 1. The four classes of laryngeal exposures as seen during laryngoscopy: grade 1, normal exposure of glottis;
grade 2, partial exposure of glottis; grade 3, epiglottis visualized but glottis not seen; grade 4, epiglottis not visualized.
Intubation-Related Anesthetic Catastrophe@
Author(s)
Country
Green RA, Taylor THa
U.K. Australia U.S.A.
Holland Rb Solazzi RW, Ward RJc
Claims from the Medical Protection Society. bCoroner’s records from New South Wales. l mm ST segment depression), pulmonary aspiration of gastric contents, tracheal injury, and esophageal intubation. The two-tailed t-test was used to compare the percent change in data from preinduction to postintubation between the simulation group and the control group. The intubation success of the simulation group 24
J. Clin. Anesth., vol. 2, JanlFeb
1990
compared with that of the control group was analyzed by the Fisher’s exact test.
Results There were no significant differences in age and ASA physical status between the two groups (Table 2). Percent changes in HR, BP, oxygen saturation and from preinduction to postintubation were not significantly different between the simulation group and the control group (Table 3). There were no cases of hypoxemia, myocardial ischemia, pulmonary aspiration of gastric contents, or tracheal injury. There were live esophageal intubations in the 20 patients on whom the simulation was performed, compared with no esophageal intubations in the control group (Table 4). This difference was statistically significant (p = 0.001). There was no evidence of hypoxemia, arrhythmias, myocardial ischemia, or pulmonary aspiration of gastric contents associated with the esophageal intubations. All five patients were successfully reintubated on the first attempt. On intubation, one patient in the control group showed evidence of a junctional rhythm. Also, one patient undergoing simulated intubation experienced a brief period of supraventricular tachycardia, which the supervising anesthesiologist believed to be unrelated to the simulation, since it occurred after successful endotracheal intubation. There was no evidence of myocardial ischemia or hemodynamic instability caused by the arrhythmias.
Discussion Evidence of airway injury, loss of airway control, hemodynamic instability, myocardial &hernia, and oxygen desaturation were considered as risks to patients participating in the simulation drill described by Cormack and Lehane.* The investigators were surprised to discover that five esophageal intubations ocTable 2. Age and ASA Physical Status of Subjects in the Study
Age* ASA physical status (I, II, III)+ Means 2 *p = 0.64 ‘p = 0.30
SD.
Simulation Group (II = 20)
Control Group (n = 20)
53.7 2 15.7
51.1 + 18.1
3, 10, 7
6, 8, 6
Simulationfor difficult intubation: Goldberg et al. Table 3.
Percent Change between Preintubation and Postintubation Data Simulation
Post
Pre
HR (beats/min)* SBP (mmHg)+ DBP (mmHg)* MAP (mmHg)* SaO, (%)I
77 131 80 101 99
2 ? f. r 4
Group (II = 20)
16 21 7 14 2
91 153 94 117 99
2 r 4 2 c
Control Group (n = 20) Pre
% Change
20 38 21 27 2
15 23 27 27 -0.17
* + ? 2 5
20 24 26 29 0.8
73 141 78 101 99
” I t t 2
Post 11
26 13 17 1
86 144 86 107 99
+ 18 +- 34 r 21 + 28 * 1
% Change
16 27 28 26
* ? ? +
16 28 28 24 0 ?I 0.97
Means k SD. Note: p values for comparison
of percent change between simulation group and control group.
*p = 0.87 ‘p = 0.63 ‘p = 0.82 ‘p = 0.94 ‘/I = 0.85 Pre = preinduction; Post = 1 minute postintubation; HR = heart rate; SBP = systolic blood pressure; MAP = mean arterial pressure; SaO, = arterial oxygen saturation.
Table 4.
Intubation Success Simulation Group (n = 20)
Tracheal intubation Esophageal intubation
15 5
Control Group (n = 20)
20 0
p = 0.001.
curred in the simulation group. These intubations could not be attributed to learning or to a single individual because they occurred randomly throughout the study with three different intubators. However, the 25% incidence of esophageal intubation has raised a number of questions. First, what are the ethical considerations of a simulation drill that may cause an esophageal intubation? According to Cormack and Lehane, “There is no risk to the patient and the time taken is similar to that for standard intubations” (p. 1108). The present authors strongly disagree and feel that informed consent should be obtained from all patients who participate in the simulation drill. Although none of the patients in this study suffered any injuries, the risks of hypoxemia, pulmonary aspiration, or gastric distention from recognized esophageal intubation were greater in the simulation group. Furthermore, an esophageal intubation clearly increases the time for a successful endotracheal intubation. Second, what should be the anesthetic management of an esophageal intubation? The investigators chose to remove the endotracheal tube immediately after recognition, believing that the risk of aspiration was
DBP = diastolic blood pressure;
less than the risk of hypoxemia and hypercarbia caused by leaving the tube in place and ventilating with a mask or attempting a second intubation without first ventilating the patient. Third, should patients volunteering for the simulation drill be protected from gastric acid aspiration with antacids, H, antagonists, and metaclopramide? Traditionally, these medications have been used prophylactically in high-risk or full-stomach patients. Subjecting volunteers to potential side effects that include inhibition of hepatic enzyme systems, potentiation of the actions of anticoagulants and phenytoin, and increased postoperative somnolence does not appear to be justified. Fourth, what would be the incidence of esophageal intubations in grade 3 exposures if an introducer were not used? Cormack and Lehane* have incorporated the use of the introducer as an essential part of their simulation drill. If the simulation drill can be practiced effectively without the aid of the introducer, elimination of the potential hazard of tracheal perforation would permit more widespread use of the drill, even though the current investigation showed no evidence of tracheal injury. Perhaps the introducer is not the answer to the grade 3 problem. The authors are currently evaluating the simulation drill without the aid of an endotracheal tube introducer. Fifth, was the high frequency of esophageal intubation caused by the investigators’ inability to perform the drill properly? One of the investigators learned the simulation drill during a rotation at the Northwick Park Hospital in London and taught it to the other investigators and trainees at the Durham Veterans Administration Medical Center. J. Clin. Anesth.,
vol. 2, Jan/Feb
1990
25
Orig-kuzl Contributions
Finally, and most importantly, do the possible benefits of this training outweigh the potential hazards of esophageal intubation ? The authors agree with Cormack and Lehane that it is not yet possible to prove that this drill reduces the number of failed intubations, since the rarity of this occurrence means that a study confined to one unit would take decades to collect the necessary data. Mallampati et al.” studied the hindered views of the faucial pillars, soft palate, and uvula produced by a large tongue as a clinical sign to predict difficult tracheal intubation. In 210 ASA I and II patients, they identified 9 (4.3% of the total patients) in whom the glottis could not be exposed by direct laryngoscopy. In all these patients, the uvula could not be visualized. If nonvisualization of the uvula helps to predict the grade 3 exposure, should the airway of a patient who is at high risk for pulmonary aspiration and whose uvula is obscured by the tongue be intubated while awake? With the patient anesthetized, encountering a grade 3 exposure may have a 1 in 4 chance of unsuccessful intubation. The authors believe that an esophageal intubation in a patient with a full stomach greatly increases the risk of aspiration. Careful consideration should be given to performing an awake intubation in a patient with these anesthetic problems. The investigators chose not to standardize induction techniques, muscle relaxants, or anesthesia personnel in order to demonstrate that this simulation drill may be used in a variety of clinical situations. Furthermore, they hope that this simulation can serve as a model to evaluate devices used for unexpected difficult intubations leading to scientific rather than anecdotal justification for their use. Whether the simulated grade 3 represents the same hidden anatomy and poses the same obstacles to successful intubation as that of the nonsimulated grade 3 exposure cannot be easily demonstrated and may be a limitation of this type of drill. In conclusion, failure to expose the glottis during laryngoscopy (grade 3 view) is an unpredictable complication that may be the harbinger of an airway catastrophe. The authors believe that the simulation drill
26
J. Clin. Anesth., vol. 2, Jan/Feb 1990
devised by Cormack and Lehane is an honest attempt at improving the anesthesiologist’s skill at successful intubation without glottic visualization. However, this simulation drill is associated with an unexpectedly high incidence of esophageal intubation. Although the drill has been uncomplicated thus far, the etiology and risks of esophageal intubation associated with it must be investigated further before it can be recommended for widespread use in the training of anesthetists in this country.
Acknowledgment The authors wish to thank James E. Linthicum of the Durham Veterans Administration Medical Center for medical illustrations.
References 1. Cheney FW, Posner K, Caplan RA, Ward RJ: Standard of care and anesthesia liability. JAMA 1989;26 1: 15991633.
Utting JE, Gray TC, Shelly FC: Human misadventure in anesthesia. Can Anaesth Sot J 1979;26:472-8. Pierce EC, Cooper JB, eds: Analysis of anesthetic mishaps. Int Anesthesiol Clin 1984;22:43-89. White A, Kander PL: Anatomical factors in difficult direct laryngoscopy. Br J Anaesth 1975;47:468-74. Birmingham PK, Cheney FW, Ward RJ: Esophageal intubation: a review of detection techniques. Anesth Analg 1986;65:886-91. 6. Linko K, Paloheimo M, Tammisto T.: Capnography for detection of accidental oesophageal intubation. Acta Anaesthesiol Stand 1983;27:199-202. Falk JL, Rackow EC, Weil MH: End-tidal carbon dioxide concentration during cardiopulmonary resuscitation. N Engl J Med 1988;318:607-11. Cormack RS, Lehane J: Difficult tracheal intubation in obstetrics. Anaesthesia 1984;39: 1105-l 1. Mallampati SR, Gatt SP, Gugino LD, et al: A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anuesth Sot J 1985;32:429-34.
