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Controversies in out-of-hospital emergency airway control: Esophageal obstruction or endotracheal intubation?
SESSION 2: Airway and Initial Drug Management
Controversies in Out-of-Hospital Emergency Airway Control: Esophageal Obstruction or Endotracheal Intubation? Roger Dean White, MD, FACC / Rochester, Minnesota
Maintaining an unobstructed airway and providing adequate oxygenation and CO 2 elimination, by artificial means if necessary, are among the highest priorities in all life-threatening circumstances. How this goal can best be met in the prehospital setting has become a controversial issue. The esophageal obturator airway (EOA ®) frequently is used in the prehospital setting, but its use and effectiveness recently have been criticized. A critical review of available literature reveals two areas of concern: 1) many clinical studies do not address prehospital airway management, and 2) the EOA has only one advantage over mask techniques for artificial ventilation, ie, it reduces the likelihood of aspiration of gastric contents. This advantage was the only one postulated by initial investigators. Many perceived EOA problems are due to poor mask fit and can be rectified. Although endotracheal intubation is the accepted standard for airway management in the apneic patient, its limitations in the prehospital setting are many. These utilization problems and complications remain undefined and must be addressed. [White RD: Controvezsies in out-of-hospital emergency airway control: Esophageal obstruction or endotracheal intubation? Ann Emerg Med September 1984 (Part 2);13:778-781. Key words: airway management; cardiopulmonary resuscitation.]
Introduction It is agreed universally that restoration and maintenance of an unobstructed airway and provision of adequate oxygenation and ventilation are the highest priorities in virtually every life-threatening circumstance. We are still struggling, however, to identify the procedures and devices that will enable us to meet this urgent priority in the widest possible number and variety of situations. The dilemma is further compounded when airway control devices are introduced into out-of-hospital practice without adequate prior assessment of their efficacy and, perhaps most importantly, their limitations. At the other extreme is the simplistic and poorly thought out declaration that anything short of direct laryngoscopy and endotracheal intubation is From the Department of Anesthesiology, Mayo Medical School, Rochester, Minnesota. Address for reprints: Roger D White, MD, Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota 55905. 13:9September 1984 (Part 2)
inadequate for airway control in emergencies requiring invasive instrmnentation. The plethora of devices on the market today clearly attests to the complexity and magnitude of the problem and the elusive nature of its solution. At the moment the major controversy seems to center on the esophageal obturator airway (EOA ®) and its cotmterpart, the esophageal gastric-tube airway (EGTA®). This discussion will approach this controversial aspect of emergency airway management in light of what is now known about esophageal obstruction with obturator airways and endotracheal intubation in out-of-hospital emergency settings. By putting both procedures into proper perspective, we hope to reach a more objective conclusion regarding out-of-hospital emergency airway management.
The Esophageal Obturator Airway The EOA was developed to provide a means of airway control in situations in which endotracheal intubation is not feasible. 1 The first published independent experimental assessment of esophageal obstruction was accomplished in dogs using a Foley catheter with a 30-mL balloon. The conclusions were clear: 1) endotracheal intubation is the method of choice for airway control during cardiac arrest and should be utilized whenever possible; and 2) when endotracheal intubation is not feasible, esophageal obstruction provides the definite advantage over standard mask ventilation of preventing aspiration of regurgitated gastric contents, g No claim was (or could have been) made regarding the superiority of esophageal obstruction in oxygenation and ventilation. In 1976 a clinical evaluation of the EOA was reported. 3 There unfortunately were only six patients in this study, and all were evaluated after admission to the emergency department. It is difficult to compare arterial blood gas values obtained during ventilation with the EOA and those following endotracheal intubation, but the authors did note some elevated arterial carbon dioxide tension (PaCO2) during ventilation using the EOA. No other conclusions are permissible from this limited study, but this observation alone was an indication that ventilation of arrested patients using an EOA may be accompanied by elevated PaCO 2 as a consequence of alveolar hypoventilation. Curiously, in spite of this apparent precaution widespread
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Fig. The pharyngeo-tracheal lumen airway in place. The lower cuff obstructs the esophagus, and the large-volume upper cuff seals the pharynx. Oropharyngeal ventilation is accomplished by means of the shorter tube without the need for a mask seal against the face. (Reproduced with permission from Eugene N Scarberry.) out-of-hospital use of the EOA was continued and was followed by a shift of focus from the adequacy of oxygenation and ventilation to a concern about a variety of mechanical complications. This concern was the inevitable consequence of rapidly disseminated implementation of esophageal obstruction with the EOA. Initial reports centered on esophageal lacerations and perforations. 46 Other complications were identified subsequently. These included unrecognized tracheal intubation, z gastric rupture due to cuff failure, s anterior displacement of the trachea and larynx,9 and upper airway obstruction secondary to a user's modification of the device.lO The frequency of these complications cannot be determined from these reports. A more recent prospective study of 106 patients who had an EOA in place provides some statistical information.n In autopsies on 70 of these patients no cases of esophageal rupture were noted. Mucosal lacerations were seen in 10% (7/70}. The trachea was intubated accidentally in 4% of patients (3/70). In another 4% the EOA could not be inserted or the "fit" was considered too tight. This prospective study provides the best quantitative assessment of major complications. In 1978 a clinical comparison of the EOA with a standard anesthesia mask and oropharyngeal airway suggested some serious technical difficulties with the EOA.~2 In ten anesthetized patients leakage around the EOA m a s k was frequent and often substantial, and accounted for lifethreatening reductions in tidal volume in two patients. The mask-to-face fit was identified by these clinicians as a major deficiency of the EOA, and the cause of its most serious limitations. They stressed that placement of the EOA does not assure airway patency. Meislin 13 assessed the respiratory effectiveness of the EOA in a comparison with endotracheal intubation in patients in the emergency department. He concluded that in this setting ventilation with the EOA is as effective as that with endotracheal intubation. Yet a review of his blood gas data reveals that 50% (11/22) of his patients had elevated PaCO 2 (/> 45 m m Hg) during ventilation with the EOA; in nine of these the PaCOz was lowered at least partially after endotracheal intubation. Smith and associates 14 made a similar comparative assessment of oxygenation and ventilation using an EOA followed by an endotracheal tube. They studied a group of patients who had sustained out-of-hospital cardiorespiratory arrest and were admitted to the emergency department, where arterial blood gas measurements were made. Based on the initial blood gas measurements and the improvement noted after endotracheal intubation, they concluded that the EOA provides inferior and inadequate ventilation. The same conclusion was reached by Auerbach and Geehr is in an almost identical clinical study format. Both studies unfortunately have intrinsic limitations. As Smith et all4 correctly acknowledge in their paper, no studies compare use of the EOA and the endotracheal tube in out-of-hospital settings relative to oxygenation and ventilation as assessed by serial measurements of arterial blood gases. Current circumstances make it virtually impossible to obtain arterial 32/779
blood during the out-of-hospital management of emergencies. The observations in these two studies do not allow us to compare the efficacy of ventilation with the EOA and the endotracheal tube in the out-of-hospital setting. Arterial blood gases of patients in whom obturator airways had been inserted in out-of-hospital cardiac arrest were measured immediately after the arrival in the emergency department. Thus these measurements were made after the worst possible period for degeneration of arterial blood gases, ie, the transport of arrested patients in an ambulance and from the ambulance into the emergency department. Deterioration of arterial blood gases has been observed frequently in intubated patients being transported from the operating room to intensive care units after open heart surgery. In these situations patients are being ventilated manually with fractional inspired concentrations of oxygen of 1.0; blood gases still deteriorate during transport. Comparison of arterial blood gases obtained immediately on arrival in the hospital following a period of CPR in a moving ambulance with those obtained five minutes or more after endotracheal intubation in the emergency department is clearly fallacious, and permits no comparative conclusions. Nevertheless their observations parallel others discussed earlier, and are further evidence that the insertion of an EOA does not assure an adequate airway; hypoventilation and even inadequate oxygenation frequently may accompany the use of this device. What can we conclude regarding the role of the EOA (or EGTA) in current out-of-hospital emergency medical practice? The EOA has only one advantage over mask techniques of ventilation: it reduces the likelihood of aspiration of regurgitated gastric contents. Somewhat ironically this was precisely the point made by the investigators who first experimentally evaluated esophageal obstruction! 2 Otherwise the EOA demands the same degree of intense vigilance and skill to maintain a tight seal of the mask against the face. It often requires two hands to secure the mask against the face in order to obtain an adequate seal. Difficulty with this mandatory skill probably accounts for most of the problems with ventilation using the obturator airway, and may result in inadequate tidal volumes. A redesigned face
Annals of Emergency Medicine
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mask would simplify and facilitate ventilation and assure higher tidal volumes. Adaptation of the Seal-Easy® face mask would appear to provide a potential resolution to this problem. The excellent prospective study by Donen and his associates n indicates that with meticulous attention to details in initial training in the use of the EOA, the incidence of tracheal intubation can be reduced dramatically to as low as 0.004%. They also documented a very low incidence of esophageal inju~, a reduction in the frequency of regurgitation and aspiration, and adequate ventilation as determined by PaCO z measurement.
Endotracheal Intubation Endotracheal intubation remains the definitive procedure for airway control in the majority of emergencies in which invasive maneuvers are indicated. Whenever circumstances permit utilization of this technique, it is without question the method of first choice, as was stated clearly in the first experimental study of esophageal obstruction. 2 Jacobs and associates 16 have shown that endotracheal intubation can be accomplished by emergency medical technician-paramedics (EMT-Ps) in the out-of-hospital environment with a high degree of success (97%). They pointed out, and it must be underscored, that acquisition and maintenance of this technical skill necessitates intensive initial training with adequate teaching resources and enough patients to maintain proficiency. In their study each EMT-P performed approximately 1.6 field intubations per month. Their observations tell us nothing about the effectiveness of endotracheal intubation in providing good oxygenation and ventilation in out-of-hospital emergencies and make no comparison with use of the EOA. Their findings point out only that under the highly controlled conditions of their study, after intensive training and with ongoing field experience in a highpatient-volume setting, the skill of endotracheal intubation can be acquired and applied by EMT-Ps. No further conclusions are permissible from their observations. If endotracheal intubation is used on a widespread basis in out-of-hospital emergency care, we can anticipate an increase in the number of reports of complications, as we have seen with the EOA. These reports undoubtedly will underestimate the frequency and magnitude of many complications, such as the time consumed in abortive attempts at intubation and, of course, the gravest complication, esophageal intubation. There is no reason to believe that widespread experience with endotracheal intubation would lead to an incidence of complications different than those we have seen With use of the EOA. Indeed, complications from attempted intubation of the trachea may turn out to be far graver and have a higher incidence than those that have been seen and reported with use of the EOA. 17-w An alternative to the EOA that is designed to avoid the problem of a mask seal has been developed. The pharyngeotracheal lumen (PTL} airway (Figure) is a double lumen tube with two cuffs. Blind insertion provides either endotracheal intubation or esophageal obstruction. Inflation of the largevolume upper cuff permits a seal of the upper airway without a mask fit against the face, a distinct advantage over the EOA. Akhough there is no reported field experience with this device, preliminary observations in anesthetized patients suggest that it is capable of providing a good airway seal and efficient gas exchange. 2° More data based on field experience obviously are needed before this device can be recommended confidently as an advantageous akemative to the EOA and endotracheal intubation. 13:9 September 1984 (Part 2)
Conclusions The critical questions regarding the obturator airway and the endotracheal tube in out-of-hospital emergencies remain unanswered. In circumstances such as those of the emergency medical services (EMS) system in Jacobs' study, endotracheal intubation seems totally reasonable36 To recommend extension of this skill to all other EMS environments is unwarranted, and the EOA may remain the airway of choice. Extensive field experience with endotracheal intubation has convinced many of us not only of the need for initial training that includes mukiple opportunities to execute this skill under supervision, but also of the equally compelling need for ongoing opportunities in the field in order to maintain and perfect this skill. It is time for the advocates of EOAs and those of endotracheal tubes to step back and acknowledge the limitations of both devices in out-of-hospital settings with regard to ongoing proficiency of insertion, adequacy of gas exchange, and the incidence and types of complications. In many EMS systems it may be advantageous to institute airway control and ventilation with the EOA and intubate the trachea when back-up personnel arrive to assist with equipment set-up and suctioning. When the EOA is used, however, meticulous and constant attention is necessary to maintain a tight seal of the mask against the face to assure the delivery of adequate tidal volumes. Endotracheal intubation remains the method of choice for airway control, and it should be used whenever training, retraining, and patient exposure permit acquisition and maintenance of this skill. Those who choose this route of airway management must begin to do prospective, controlled studies in the out-of-hospital environment to document the frequency of prompt and proper insertion, adequacy of oxygenation and ventilation, and complications. Until such data are available no broad statement can be made about the appropriateness of the application of this skill in field circumstances. In any case endotracheal intubation is not, and will never be, feasible in all situations. The EOA can be used if its limitations are recognized and its complications minimized through more intensive initial training, n Available evidence strongly indicates that redesign of the EOA face mask is needed in order to improve delivered tidal volumes.
References
1. Don Michael TA, Lambert EH, Mehran A: "Mouth-to-lung airway" for cardiac resuscitation. Lancet 1968;2:1329. 2. Greenbaum DM, Poggi J, Grace WJ: Esophageal obstruction during oxygen administration: A new method for use in resuscitation. Chest 1974:65;188-191. 3. Schofferman J, Oill P, Lewis AJ: The esophageal obturator airway: A clinical evaluation. Chest 1976;69:67-71. 4. Johnson KR Jr, Genovesi MG, Lassar KH: Esophageal obturator airway: Use and complications. JACEP 1976;5:36-39. 5. Pitcher DB, DeMeules JE: Esophageal perforation following use of esophageal airway. Chest 1976;69:377-380. 6. Strate RG, Fischer RP: Midesophageal perforations by esophageal obturator airways. ] Trauma 1976:16;503-511. 7. Yancey W, Wears R, Kamajian G, et al: Unrecognized tracheal intubation: A complication of the esophageal obturator airway. Ann Emerg Med 1980;9:18-20. 8. Crippen D, Olvey S, Graffis R: Gastric rupture: An esophageal obturator airway complication. Ann Emerg Med 1981;10:370-373.
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9. Low RB, Jensen RD, Cavanaugh KJ: Marked anterior displacement of the trachea and larynx from an esophageal obturator airway (EOA). Ann Emerg Med 1982;11:670-672. 10. Berkebile PE, Narla R: An unusual complication of esophageal obturator airway (EOA). Anesthesiology 1982;57:414-415. 11. Donen N, Tweed A, Dashfsky S, et ah The esophageal obturator airway: An appraisal. Can Anaesth Soc J 1983;30:194-200. 12. Bryson TK, Benumof JL, Ward CF: The esophageal obturator airway: A clinical comparison to ventilation with a mask and oropharyngeal airway. Chest 1978;74:537-539. 13. Meislin HW: The esophageal obturator airway: A study of respiratory effectiveness. Ann Emerg Med 1980;9:54-59. 14. Smith JP, Bodai BI, Augourg R, et ah A field evaluation of the esophageal obturator airway. J Trauma 1983;23:317-321. 15. Auerbach PS, Geehr EC: Inadequate oxygenation and ventila-
tion using the esophageal gastric tube airway in the prehospital setting. JAMA 1983;250:3067-3071. 16. Jacobs LM, Berrizbeitia LD, Bennett B, et ah Endotracheal intubation in the prehospital phase of emergency medical care. JAMA 1983;250:2175-2177. 17. Taryle DA, Chandler JE, Good JT, et al: Emergency room intubations - - complications and survival. Chest 1979;75:541-543. 18. Stauffer JL, Petty TL: Accidental intubation of the pyriform sinus: A complication of "roadside" resuscitation. JAMA 1977; 237:2324-2325. 19. Pollard BJ, Junius F: Accidental intubation of the oesophagus. Anaesth Intensive Care 1980;8:183-186. 20. Niemann JT, Rosborough JP, Myers R, et al: The pharyngeotracheal lumen airway: Preliminary investigation of a new adjunct. Ann Emerg Med 1984;13:591-596.
Effects of Acidemia and Sodium Bicarbonate Therapy in Advanced Cardiac Life Support James T Niemann, MD* / Torrance, California / John P Rosborough, PhD1- / Houston, Texas
Cardiac output using the currently recommended closedchest cardiopulmonary resuscitation (CPR) technique is marginal (< 30% of control), and eventually will result in tissue hypoperfusion and lactic acidemia. Intermittent sodium bicarbonate administration currently is recommended for treatment of this metabolic acidemia, and based on available data recommended dosages are empiric but sound. In this review the potential complications of acidemia and sodium bicarbonate administration are considered from the viewpoint of resuscitation outcome. In our opinion, available data are limited, and further evaluation and consideration of sodium bicarbonate requirements in the resuscitation setting are required. [Niemann JT, Rosborough JP: Effects of acidemia and sodium bicarbonate therapy in advanced cardiac life support. Ann Emerg Med September 1984 (Part 2);13:781-784. Key words: acid-base balance; cardiopulmonary resuscitation; sodium bicarbonate.]
Introduction Cardiac output during circulatory arrest and closed-chest artificial circulatory support is less than 30% of values measured during sinus r h y t h m in animals and h u m a n subjectsA -4 Tissue hypoperfusion and lactic acidemia will inFrom the Department of Emergency Medicine, Harbor-UCLA Medical Center, Torrance, California;* and the Department of Physiology, Baylor College of Medicine, Houston, Texas.t Address for reprints: James T Niemann, MD, Department of Emergency Medicine, Harbor-UCLA Medical Center, 1000 West Carson Street, Torrance, California 90509. 34/781
variably result if closed-chest resuscitation efforts are prolonged by prehospital rescuers and emergency department personnel. Intermittent sodium bicarbonate (NaHCO3) administration is used to treat this metabolic acidemia, s Arterial pH cannot be predicted during arrest and resuscitation, however, because it is related to the duration of circulatory arrest and cardiopulmonary resuscitation (CPR), the adequacy of artificial circulation and ventilation, the pH prior to arrest, and the concentration of N a H C O 3 administered and its volume of distribution. 6 Current dosage recommendations are largely intuitive because few clinical studies have addressed the time course of acid-base changes during cardiopulmonary arrest and resuscitation attempts. Most of these studies were performed in hospitalized, critically ill patients, and thus may not be directly applicable to prehospital and emergency department settings. 6-8 Current recommendations regarding N a H C O 3 therapy can be viewed only as clinical "best guesses," because available data neither support nor clearly refute current recommendations. We review the potential adverse effects of acidemia and N a H C O 8 administration.
Effects of Metabolic Acidemia During Resuscitation Potential adverse effects of acidemia during cardiopulmonary arrest and resuscitation attempts include depressed myocardial contractility,9,1o lowered ventricular fibrillation threshold, n attenuated pressor response to administered catecholamines, m and increased ventricular defibrillation thresholdA 8 In the setting of ventricular fibrillation and resuscitation, the first two concerns are more theoretical than real. The
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Controversies in Out-of-Hospital Emergency Airway Control: Esophageal Obstruction or Endotracheal Intubation? Roger Dean White, MD, FACC / Rochester, Minnesota
Maintaining an unobstructed airway and providing adequate oxygenation and CO 2 elimination, by artificial means if necessary, are among the highest priorities in all life-threatening circumstances. How this goal can best be met in the prehospital setting has become a controversial issue. The esophageal obturator airway (EOA ®) frequently is used in the prehospital setting, but its use and effectiveness recently have been criticized. A critical review of available literature reveals two areas of concern: 1) many clinical studies do not address prehospital airway management, and 2) the EOA has only one advantage over mask techniques for artificial ventilation, ie, it reduces the likelihood of aspiration of gastric contents. This advantage was the only one postulated by initial investigators. Many perceived EOA problems are due to poor mask fit and can be rectified. Although endotracheal intubation is the accepted standard for airway management in the apneic patient, its limitations in the prehospital setting are many. These utilization problems and complications remain undefined and must be addressed. [White RD: Controvezsies in out-of-hospital emergency airway control: Esophageal obstruction or endotracheal intubation? Ann Emerg Med September 1984 (Part 2);13:778-781. Key words: airway management; cardiopulmonary resuscitation.]
Introduction It is agreed universally that restoration and maintenance of an unobstructed airway and provision of adequate oxygenation and ventilation are the highest priorities in virtually every life-threatening circumstance. We are still struggling, however, to identify the procedures and devices that will enable us to meet this urgent priority in the widest possible number and variety of situations. The dilemma is further compounded when airway control devices are introduced into out-of-hospital practice without adequate prior assessment of their efficacy and, perhaps most importantly, their limitations. At the other extreme is the simplistic and poorly thought out declaration that anything short of direct laryngoscopy and endotracheal intubation is From the Department of Anesthesiology, Mayo Medical School, Rochester, Minnesota. Address for reprints: Roger D White, MD, Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota 55905. 13:9September 1984 (Part 2)
inadequate for airway control in emergencies requiring invasive instrmnentation. The plethora of devices on the market today clearly attests to the complexity and magnitude of the problem and the elusive nature of its solution. At the moment the major controversy seems to center on the esophageal obturator airway (EOA ®) and its cotmterpart, the esophageal gastric-tube airway (EGTA®). This discussion will approach this controversial aspect of emergency airway management in light of what is now known about esophageal obstruction with obturator airways and endotracheal intubation in out-of-hospital emergency settings. By putting both procedures into proper perspective, we hope to reach a more objective conclusion regarding out-of-hospital emergency airway management.
The Esophageal Obturator Airway The EOA was developed to provide a means of airway control in situations in which endotracheal intubation is not feasible. 1 The first published independent experimental assessment of esophageal obstruction was accomplished in dogs using a Foley catheter with a 30-mL balloon. The conclusions were clear: 1) endotracheal intubation is the method of choice for airway control during cardiac arrest and should be utilized whenever possible; and 2) when endotracheal intubation is not feasible, esophageal obstruction provides the definite advantage over standard mask ventilation of preventing aspiration of regurgitated gastric contents, g No claim was (or could have been) made regarding the superiority of esophageal obstruction in oxygenation and ventilation. In 1976 a clinical evaluation of the EOA was reported. 3 There unfortunately were only six patients in this study, and all were evaluated after admission to the emergency department. It is difficult to compare arterial blood gas values obtained during ventilation with the EOA and those following endotracheal intubation, but the authors did note some elevated arterial carbon dioxide tension (PaCO2) during ventilation using the EOA. No other conclusions are permissible from this limited study, but this observation alone was an indication that ventilation of arrested patients using an EOA may be accompanied by elevated PaCO 2 as a consequence of alveolar hypoventilation. Curiously, in spite of this apparent precaution widespread
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ESOPHAGEAL OBSTRUCTION OR ENDOTRACHEAL INTUBATION White
Fig. The pharyngeo-tracheal lumen airway in place. The lower cuff obstructs the esophagus, and the large-volume upper cuff seals the pharynx. Oropharyngeal ventilation is accomplished by means of the shorter tube without the need for a mask seal against the face. (Reproduced with permission from Eugene N Scarberry.) out-of-hospital use of the EOA was continued and was followed by a shift of focus from the adequacy of oxygenation and ventilation to a concern about a variety of mechanical complications. This concern was the inevitable consequence of rapidly disseminated implementation of esophageal obstruction with the EOA. Initial reports centered on esophageal lacerations and perforations. 46 Other complications were identified subsequently. These included unrecognized tracheal intubation, z gastric rupture due to cuff failure, s anterior displacement of the trachea and larynx,9 and upper airway obstruction secondary to a user's modification of the device.lO The frequency of these complications cannot be determined from these reports. A more recent prospective study of 106 patients who had an EOA in place provides some statistical information.n In autopsies on 70 of these patients no cases of esophageal rupture were noted. Mucosal lacerations were seen in 10% (7/70}. The trachea was intubated accidentally in 4% of patients (3/70). In another 4% the EOA could not be inserted or the "fit" was considered too tight. This prospective study provides the best quantitative assessment of major complications. In 1978 a clinical comparison of the EOA with a standard anesthesia mask and oropharyngeal airway suggested some serious technical difficulties with the EOA.~2 In ten anesthetized patients leakage around the EOA m a s k was frequent and often substantial, and accounted for lifethreatening reductions in tidal volume in two patients. The mask-to-face fit was identified by these clinicians as a major deficiency of the EOA, and the cause of its most serious limitations. They stressed that placement of the EOA does not assure airway patency. Meislin 13 assessed the respiratory effectiveness of the EOA in a comparison with endotracheal intubation in patients in the emergency department. He concluded that in this setting ventilation with the EOA is as effective as that with endotracheal intubation. Yet a review of his blood gas data reveals that 50% (11/22) of his patients had elevated PaCO 2 (/> 45 m m Hg) during ventilation with the EOA; in nine of these the PaCOz was lowered at least partially after endotracheal intubation. Smith and associates 14 made a similar comparative assessment of oxygenation and ventilation using an EOA followed by an endotracheal tube. They studied a group of patients who had sustained out-of-hospital cardiorespiratory arrest and were admitted to the emergency department, where arterial blood gas measurements were made. Based on the initial blood gas measurements and the improvement noted after endotracheal intubation, they concluded that the EOA provides inferior and inadequate ventilation. The same conclusion was reached by Auerbach and Geehr is in an almost identical clinical study format. Both studies unfortunately have intrinsic limitations. As Smith et all4 correctly acknowledge in their paper, no studies compare use of the EOA and the endotracheal tube in out-of-hospital settings relative to oxygenation and ventilation as assessed by serial measurements of arterial blood gases. Current circumstances make it virtually impossible to obtain arterial 32/779
blood during the out-of-hospital management of emergencies. The observations in these two studies do not allow us to compare the efficacy of ventilation with the EOA and the endotracheal tube in the out-of-hospital setting. Arterial blood gases of patients in whom obturator airways had been inserted in out-of-hospital cardiac arrest were measured immediately after the arrival in the emergency department. Thus these measurements were made after the worst possible period for degeneration of arterial blood gases, ie, the transport of arrested patients in an ambulance and from the ambulance into the emergency department. Deterioration of arterial blood gases has been observed frequently in intubated patients being transported from the operating room to intensive care units after open heart surgery. In these situations patients are being ventilated manually with fractional inspired concentrations of oxygen of 1.0; blood gases still deteriorate during transport. Comparison of arterial blood gases obtained immediately on arrival in the hospital following a period of CPR in a moving ambulance with those obtained five minutes or more after endotracheal intubation in the emergency department is clearly fallacious, and permits no comparative conclusions. Nevertheless their observations parallel others discussed earlier, and are further evidence that the insertion of an EOA does not assure an adequate airway; hypoventilation and even inadequate oxygenation frequently may accompany the use of this device. What can we conclude regarding the role of the EOA (or EGTA) in current out-of-hospital emergency medical practice? The EOA has only one advantage over mask techniques of ventilation: it reduces the likelihood of aspiration of regurgitated gastric contents. Somewhat ironically this was precisely the point made by the investigators who first experimentally evaluated esophageal obstruction! 2 Otherwise the EOA demands the same degree of intense vigilance and skill to maintain a tight seal of the mask against the face. It often requires two hands to secure the mask against the face in order to obtain an adequate seal. Difficulty with this mandatory skill probably accounts for most of the problems with ventilation using the obturator airway, and may result in inadequate tidal volumes. A redesigned face
Annals of Emergency Medicine
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mask would simplify and facilitate ventilation and assure higher tidal volumes. Adaptation of the Seal-Easy® face mask would appear to provide a potential resolution to this problem. The excellent prospective study by Donen and his associates n indicates that with meticulous attention to details in initial training in the use of the EOA, the incidence of tracheal intubation can be reduced dramatically to as low as 0.004%. They also documented a very low incidence of esophageal inju~, a reduction in the frequency of regurgitation and aspiration, and adequate ventilation as determined by PaCO z measurement.
Endotracheal Intubation Endotracheal intubation remains the definitive procedure for airway control in the majority of emergencies in which invasive maneuvers are indicated. Whenever circumstances permit utilization of this technique, it is without question the method of first choice, as was stated clearly in the first experimental study of esophageal obstruction. 2 Jacobs and associates 16 have shown that endotracheal intubation can be accomplished by emergency medical technician-paramedics (EMT-Ps) in the out-of-hospital environment with a high degree of success (97%). They pointed out, and it must be underscored, that acquisition and maintenance of this technical skill necessitates intensive initial training with adequate teaching resources and enough patients to maintain proficiency. In their study each EMT-P performed approximately 1.6 field intubations per month. Their observations tell us nothing about the effectiveness of endotracheal intubation in providing good oxygenation and ventilation in out-of-hospital emergencies and make no comparison with use of the EOA. Their findings point out only that under the highly controlled conditions of their study, after intensive training and with ongoing field experience in a highpatient-volume setting, the skill of endotracheal intubation can be acquired and applied by EMT-Ps. No further conclusions are permissible from their observations. If endotracheal intubation is used on a widespread basis in out-of-hospital emergency care, we can anticipate an increase in the number of reports of complications, as we have seen with the EOA. These reports undoubtedly will underestimate the frequency and magnitude of many complications, such as the time consumed in abortive attempts at intubation and, of course, the gravest complication, esophageal intubation. There is no reason to believe that widespread experience with endotracheal intubation would lead to an incidence of complications different than those we have seen With use of the EOA. Indeed, complications from attempted intubation of the trachea may turn out to be far graver and have a higher incidence than those that have been seen and reported with use of the EOA. 17-w An alternative to the EOA that is designed to avoid the problem of a mask seal has been developed. The pharyngeotracheal lumen (PTL} airway (Figure) is a double lumen tube with two cuffs. Blind insertion provides either endotracheal intubation or esophageal obstruction. Inflation of the largevolume upper cuff permits a seal of the upper airway without a mask fit against the face, a distinct advantage over the EOA. Akhough there is no reported field experience with this device, preliminary observations in anesthetized patients suggest that it is capable of providing a good airway seal and efficient gas exchange. 2° More data based on field experience obviously are needed before this device can be recommended confidently as an advantageous akemative to the EOA and endotracheal intubation. 13:9 September 1984 (Part 2)
Conclusions The critical questions regarding the obturator airway and the endotracheal tube in out-of-hospital emergencies remain unanswered. In circumstances such as those of the emergency medical services (EMS) system in Jacobs' study, endotracheal intubation seems totally reasonable36 To recommend extension of this skill to all other EMS environments is unwarranted, and the EOA may remain the airway of choice. Extensive field experience with endotracheal intubation has convinced many of us not only of the need for initial training that includes mukiple opportunities to execute this skill under supervision, but also of the equally compelling need for ongoing opportunities in the field in order to maintain and perfect this skill. It is time for the advocates of EOAs and those of endotracheal tubes to step back and acknowledge the limitations of both devices in out-of-hospital settings with regard to ongoing proficiency of insertion, adequacy of gas exchange, and the incidence and types of complications. In many EMS systems it may be advantageous to institute airway control and ventilation with the EOA and intubate the trachea when back-up personnel arrive to assist with equipment set-up and suctioning. When the EOA is used, however, meticulous and constant attention is necessary to maintain a tight seal of the mask against the face to assure the delivery of adequate tidal volumes. Endotracheal intubation remains the method of choice for airway control, and it should be used whenever training, retraining, and patient exposure permit acquisition and maintenance of this skill. Those who choose this route of airway management must begin to do prospective, controlled studies in the out-of-hospital environment to document the frequency of prompt and proper insertion, adequacy of oxygenation and ventilation, and complications. Until such data are available no broad statement can be made about the appropriateness of the application of this skill in field circumstances. In any case endotracheal intubation is not, and will never be, feasible in all situations. The EOA can be used if its limitations are recognized and its complications minimized through more intensive initial training, n Available evidence strongly indicates that redesign of the EOA face mask is needed in order to improve delivered tidal volumes.
References
1. Don Michael TA, Lambert EH, Mehran A: "Mouth-to-lung airway" for cardiac resuscitation. Lancet 1968;2:1329. 2. Greenbaum DM, Poggi J, Grace WJ: Esophageal obstruction during oxygen administration: A new method for use in resuscitation. Chest 1974:65;188-191. 3. Schofferman J, Oill P, Lewis AJ: The esophageal obturator airway: A clinical evaluation. Chest 1976;69:67-71. 4. Johnson KR Jr, Genovesi MG, Lassar KH: Esophageal obturator airway: Use and complications. JACEP 1976;5:36-39. 5. Pitcher DB, DeMeules JE: Esophageal perforation following use of esophageal airway. Chest 1976;69:377-380. 6. Strate RG, Fischer RP: Midesophageal perforations by esophageal obturator airways. ] Trauma 1976:16;503-511. 7. Yancey W, Wears R, Kamajian G, et al: Unrecognized tracheal intubation: A complication of the esophageal obturator airway. Ann Emerg Med 1980;9:18-20. 8. Crippen D, Olvey S, Graffis R: Gastric rupture: An esophageal obturator airway complication. Ann Emerg Med 1981;10:370-373.
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ESOPHAGEAL OBSTRUCTION OR ENDOTRACHEAL INTUBATION White
9. Low RB, Jensen RD, Cavanaugh KJ: Marked anterior displacement of the trachea and larynx from an esophageal obturator airway (EOA). Ann Emerg Med 1982;11:670-672. 10. Berkebile PE, Narla R: An unusual complication of esophageal obturator airway (EOA). Anesthesiology 1982;57:414-415. 11. Donen N, Tweed A, Dashfsky S, et ah The esophageal obturator airway: An appraisal. Can Anaesth Soc J 1983;30:194-200. 12. Bryson TK, Benumof JL, Ward CF: The esophageal obturator airway: A clinical comparison to ventilation with a mask and oropharyngeal airway. Chest 1978;74:537-539. 13. Meislin HW: The esophageal obturator airway: A study of respiratory effectiveness. Ann Emerg Med 1980;9:54-59. 14. Smith JP, Bodai BI, Augourg R, et ah A field evaluation of the esophageal obturator airway. J Trauma 1983;23:317-321. 15. Auerbach PS, Geehr EC: Inadequate oxygenation and ventila-
tion using the esophageal gastric tube airway in the prehospital setting. JAMA 1983;250:3067-3071. 16. Jacobs LM, Berrizbeitia LD, Bennett B, et ah Endotracheal intubation in the prehospital phase of emergency medical care. JAMA 1983;250:2175-2177. 17. Taryle DA, Chandler JE, Good JT, et al: Emergency room intubations - - complications and survival. Chest 1979;75:541-543. 18. Stauffer JL, Petty TL: Accidental intubation of the pyriform sinus: A complication of "roadside" resuscitation. JAMA 1977; 237:2324-2325. 19. Pollard BJ, Junius F: Accidental intubation of the oesophagus. Anaesth Intensive Care 1980;8:183-186. 20. Niemann JT, Rosborough JP, Myers R, et al: The pharyngeotracheal lumen airway: Preliminary investigation of a new adjunct. Ann Emerg Med 1984;13:591-596.
Effects of Acidemia and Sodium Bicarbonate Therapy in Advanced Cardiac Life Support James T Niemann, MD* / Torrance, California / John P Rosborough, PhD1- / Houston, Texas
Cardiac output using the currently recommended closedchest cardiopulmonary resuscitation (CPR) technique is marginal (< 30% of control), and eventually will result in tissue hypoperfusion and lactic acidemia. Intermittent sodium bicarbonate administration currently is recommended for treatment of this metabolic acidemia, and based on available data recommended dosages are empiric but sound. In this review the potential complications of acidemia and sodium bicarbonate administration are considered from the viewpoint of resuscitation outcome. In our opinion, available data are limited, and further evaluation and consideration of sodium bicarbonate requirements in the resuscitation setting are required. [Niemann JT, Rosborough JP: Effects of acidemia and sodium bicarbonate therapy in advanced cardiac life support. Ann Emerg Med September 1984 (Part 2);13:781-784. Key words: acid-base balance; cardiopulmonary resuscitation; sodium bicarbonate.]
Introduction Cardiac output during circulatory arrest and closed-chest artificial circulatory support is less than 30% of values measured during sinus r h y t h m in animals and h u m a n subjectsA -4 Tissue hypoperfusion and lactic acidemia will inFrom the Department of Emergency Medicine, Harbor-UCLA Medical Center, Torrance, California;* and the Department of Physiology, Baylor College of Medicine, Houston, Texas.t Address for reprints: James T Niemann, MD, Department of Emergency Medicine, Harbor-UCLA Medical Center, 1000 West Carson Street, Torrance, California 90509. 34/781
variably result if closed-chest resuscitation efforts are prolonged by prehospital rescuers and emergency department personnel. Intermittent sodium bicarbonate (NaHCO3) administration is used to treat this metabolic acidemia, s Arterial pH cannot be predicted during arrest and resuscitation, however, because it is related to the duration of circulatory arrest and cardiopulmonary resuscitation (CPR), the adequacy of artificial circulation and ventilation, the pH prior to arrest, and the concentration of N a H C O 3 administered and its volume of distribution. 6 Current dosage recommendations are largely intuitive because few clinical studies have addressed the time course of acid-base changes during cardiopulmonary arrest and resuscitation attempts. Most of these studies were performed in hospitalized, critically ill patients, and thus may not be directly applicable to prehospital and emergency department settings. 6-8 Current recommendations regarding N a H C O 3 therapy can be viewed only as clinical "best guesses," because available data neither support nor clearly refute current recommendations. We review the potential adverse effects of acidemia and N a H C O 8 administration.
Effects of Metabolic Acidemia During Resuscitation Potential adverse effects of acidemia during cardiopulmonary arrest and resuscitation attempts include depressed myocardial contractility,9,1o lowered ventricular fibrillation threshold, n attenuated pressor response to administered catecholamines, m and increased ventricular defibrillation thresholdA 8 In the setting of ventricular fibrillation and resuscitation, the first two concerns are more theoretical than real. The
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