The Esophageal Obturator Airway* A Clinical Evaluation Jerome Schofferman, M.D.;•• PhyUisOill, M.D.;•• and A. ]ames Lewis, M.D.••
The esophageal obturator airway (EOA) bas been considered a useful ventilatory technique for cardiopulmonary resuscitation, but quantitative analysis of its cOnical effectiveness is not available. We evaluated the EOA in 18 patients who bad suffered prebospital cardiac arrest and who were resuscitated by mobile intensive care unit paramedics employing an EOA. Arterial blood gas determinations were obtained during ventilation with the EOA and then repeated after endotracheal intubation. Arterial oxygen tension (Pa()...!) greater than 64 mm Hg was achieved
in 11 of 1l patients who had been converted to supraventricular rhythm, despite varying inspired oxygen concentrations. A PaO:l greater than 77 mm Hg was achieved in three of sb: patients stiD requiring external cardiac massage. There was Uttle or no improvement in oxygenation after endotracheal intubation, implying tlud the faUures to oxyienate were not due to the EOA. We cooelude that the EOA is a nseful adjunct during cardiopulmonary resuscitation when eudotracbeal intubatlou is not feasible.
resuscitation outside a hospital Cardiopulmonary setting presents a formidable challenge. Cur-
Ventilation with an EOA has seemed adequate by clinical criteria,7•9 but it has not been shown that adequate oxygenation can be achieved in humans. The mobile intensive care unit paramedics of Los Angeles County have been using an EOA routinely during prehospital cardiopulmonary resuscitation. Therefore, we had a unique opportunity to evaluate its effectiveness in an actual clinical setting.
rently only 25 to 65 percent of patients suffering ventricular fibrillation survive to reach a hospital, despite sophisticated systems of prehospital intensive care. l-4 Less than half of these patients are eventually discharged. Better resuscitative techniques and equipment are, therefore, constantly being developed for use by mobile rescue units. Adequate ventilation is a prerequisite for successful resuscitation; and simple, practical, and efficient means of providing adequate air exchange are necessary. Mouth-to-mouth, mouth-to-mask, or bagvalve-mask ventilation may be satisfactory, but each technique has significant drawbacks. 5 •6 Endotracheal intubation is, of course, preferred but requires skilled experienced personnel, proper positioning of the patient, and direct visualization of the glottis for orotracheal insertion of the tube. Don Michael and associates, 6 therefore, developed an esophageal occluding airway in an attempt to overcome these disadvantages. The esophageal obturator airway ( EOA) is a modification of their original "mouth-to-lung" airway. The EOA is simple to use, does not require a laryngoscope for insertion, and reduces the possibility of aspiration. °From the Receiving-Emergency Division and the Division of Cardiology, Department of Medicine, Harbor General Hospital, Torrance, Calif., and the School of Medicine, University of California, Los Angeles. • • Assistant Professor of Medicine. Manuscript received Mar 2]; revision accepted July 21. Reprint requests: Dr. Sclwfferman, Harbor General Hospital, TorTance, California 90509
CHEST, 69: 1, JANUARY, 1976
METIIODS
The EOA The EOA (Fig 1) resembles an endotracheal tube with the distal end occluded and 16 holes, each 3 mm in diameter, distributed over the section of the tube which will be positioned in the hypopharynx. The tube with face mask attached is passed into the esophagus blindly without need of a laryngoscope. The face mask is held tightly over the nose and mouth, the esophageal balloon is inflated, and ventilation is begun. Air or oxygen is blown into the open end of the tube, leaves the EOA through the small holes, and enters the trachea. The inflated esophageal balloon prevents the air from entering the stomach and also prevents vomiting. The mask prevents air from lealcing through nose or mouth. Therefore, the air must enter the trachea, which is the only unobstructed orifice ( Fig 2) . Proper positioning of the tube in the esophagus is assured if the rescuer hears adequate breath sounds and sees the chest wall rise and fall with each breath. Should the tube inadvertently be placed in the trachea, breath sounds would be absent, and the tube would be removed and reinserted. After the patient has been stabilized, and only when adequately trained personnel are at hand, the trachea should be intubated. Vomiting is common during removal of the EOA; and, therefore, it should not be removed until an
THE ESOPHAGEAL OBTURATOR AIRWAY 67
FIGURE
1. Esophageal obturator airway with syringe and face mask attached and balloon inflated.
endotracheal tube is in place with balloon inHated. Then the esophageal balloon can be deflated and the EOA removed. Study Population
Eighteen patients who were documented to have been in ventricular fibrillation or asystole at the time of arrival of mobile intensive-care-unit rescuers and who were transported to Harbor General Hospital, Torrance, Calif, were evaluated. Because patients are routinely taken to the nearest hospital after resuscitative attempts, the patients reported here form only a portion of the total community prehospital resuscitative attempts. Patients pronounced dead on arrival in the Emergency Department were not included nor were the few patients who were intubated before arterial blood could be drawn for analysis. Resuscitation and Study Procedure
All patients received primary care from highly trained mobile intensive care unit paramedics operating under the
radiotelemetric supervision of a physician or specially certified nurse at a base-station hospital.IO In each case, resuscitation in the field included basic life support plus advanced techniques which included electrical defibrillation and intravenous administration of drugs such as lidocaine, epinephrine, sodium bicarbonate, calcium chloride, and atropine. Prior to hospitalization, total ventilatory support was necessary in each patient, and the EOA was routinely used. Ventilation in the field was carried out with a portable demand valve system which delivered 100 percent oxygen. Resuscitation attempts were continued in the field until the patient was converted to a satisfactory stable rhythm or until the ventricular fibrillation or asystole was deemed refractory, in which case the patient was transported to the nearest hospital while receiving continuous cardiopulmonary resuscitation. At Harbor General Hospital, resuscitative efforts were continued by the Emergency Department's house officers and nurses plus a respiratory therapist. Frequent determinations of arterial blood gas values during cardiopulmo-
FIGURE 2. Schematic representation of EOA in proper position in patient. Air (thick arrow) blown into proximal end exits via small holes (thin arrows) and is forced down trachea, as other routes are occluded.
88 SCHOFFERMAN, OILL, LEWIS
CHEST, 69: 1, JANUARY, 1976
tal respiratory support at the time of evaluation.. The results of arterial blood gas analyses during ventilation with the EOA by a respiratory therapist in the Emergency Department are shown in Table 1. Twelve patients (group I ) had successfully undergone cardioversion to supraventricular rhythm in the field and no longer required external cardiac massage. Seven of these were being ventilated with IOO percent oxygen at the time of evaluation. The mean Pa02 in these seven patients was 268 mm Hg (range, I35 to 5IO mm Hg) . Four patients in group I received an FI02 of 0.4, and a mean Pa02 of 75 mm Hg was achieved (range, 56 to ll2 mm Hg). One patient was ventilated with room air, and the Pa02 was 8I mm Hg. The mean PaC 45 mm Hg). In addition, there was a general trend towards improvement in PaC~ after endotracheal intubation in both groups of patients. The explanation for the hypoventilation is not readily apparent. There was no evident clinical difference between the hypoventilated patients and those with normal or low PaC02. Every patient was apneic, and all required total ventilatory support. Tube mechanics might be implicated. Increased dead-space with the EOA compared to the endotracheal tube might contribute to the hypoventilation, as might unnoticed leaks around the face mask or around an underinHated esophageal balloon. A change in minute ventilation introduced by the rescuer in response to learning the initial arterial blood gas results may also have occurred. The majority of patients, however, including two patients still requiring external cardiac massage, had normal or low PaC02, demonstrating that it is very possible to achieve adequate PaC02. The data demonstrate that it is dif-
CHEST, 69: 1, JANUARY, 1976
ficult to predict accurately PaC02; and, therefore, it may be worthwhile to attempt to overventilate patients pending the availability of arterial blood gas results, as hypercapnia during cardiopulmonary resuscitation should be avoided. The results of this study are encouraging. The excellent oxygenation obtained in most patients implies that the EOA is a useful adjunct to cardiopulmonary resuscitation when endotracheal intubation is not feasible. The EOA might prove especially useful to volunteer rescue teams, to mobile intensive care unit personnel with small numbers of rescues, and to communities where large numbers of personnel must be trained. A 100 percent oxygen source is preferable, and frequent monitoring of arterial blood gas levels is desirable. ACKNOWLEDGMENTS: We would ll1c:e to thank Drs. Lucien Cuze and Eugene Nagel for their helpful review of the manuscript, Mrs. Jenny Keshishian for her valuable secretarial assistance, and the Harbor General Hospital's Emergency Department nurses and house staH who cared for these patients. REFERENCES
1 Liberthson RR, Nagel EL, Hirschman JC, et al : Pathophysiologic observations in prehospital ventricular fibrillation and sudden cardiac death. Circulation 49 :790-798, 1974 2 Adgey AA, Nelson PG, Scott ME, et al : Management of ventricular fibrillation outside hospital. Lancet 1:11691171, 1969 3 Crampton RS, Aldrich RF, Gascho JA, et al: Reduction of prehospital, ambulance and community coronarY death rates by the community-wide emergency cardiac care system. Am J Med 58: 151-165, 1975 4 Liberthson RR, Nagel EL, Hirschman JC, et al: Prehospital ventricular defibrillation : Prognosis and follow-up course. N Eng)] Med 291:317-321, 1974 5 Standards for cardiopulmonarY resuscitation (CPR) and emergency cardiac care ( ECC) . JAMA ( suppl) 227:833868, 1974 6 Don Michael T A, Lambert EH, Mehran A: "Mouth-tolung airway" for cardiac resuscitation. Lancet 2 : 1329, 1968 7 Don Michael TA, Gordon AS : Esophageal obturator airway : A new adjunct for artificial ventilation. Presented at the National Conference on Standards for Cardiopulmonary Resuscitation and Emergency Cardiac Care. Washington, DC, May 16, 1973 8 Farley M: The esophageal obturator airway. Respir Ther Nov/Dec, 1973 9 Smock SN: Esophageal obturator airway : Perferred CPR technique. J Am Coli Emergency Phys 4 :232-233, 1975 10 Lewis AJ, Ailshie G, Criley JM : Prehospital cardiac care in a paramedical mobile intensive care unit. Calif Med 117: 1-8, 1972 11 Greenbaum OM, Poggi J, Grace WJ: Communication to the editor. Chest 66:110, 1974 12 Greenbaum OM, Poggi J, Grace WJ : Esophageal obstruction during oxygen administration: A new method for use in resuscitation. Chest 65:188-191, 1974 13 Fillmore SJ, Shapiro M, Killip T : Serial blood gas studies during cardiopulmonary resuscitation. Ann Intern Med 72:465-469, 1970
THE ESOPHAGEAL OBTURATOR AIRWAY 71
The esophageal obturator airway (EOA) bas been considered a useful ventilatory technique for cardiopulmonary resuscitation, but quantitative analysis of its cOnical effectiveness is not available. We evaluated the EOA in 18 patients who bad suffered prebospital cardiac arrest and who were resuscitated by mobile intensive care unit paramedics employing an EOA. Arterial blood gas determinations were obtained during ventilation with the EOA and then repeated after endotracheal intubation. Arterial oxygen tension (Pa()...!) greater than 64 mm Hg was achieved
in 11 of 1l patients who had been converted to supraventricular rhythm, despite varying inspired oxygen concentrations. A PaO:l greater than 77 mm Hg was achieved in three of sb: patients stiD requiring external cardiac massage. There was Uttle or no improvement in oxygenation after endotracheal intubation, implying tlud the faUures to oxyienate were not due to the EOA. We cooelude that the EOA is a nseful adjunct during cardiopulmonary resuscitation when eudotracbeal intubatlou is not feasible.
resuscitation outside a hospital Cardiopulmonary setting presents a formidable challenge. Cur-
Ventilation with an EOA has seemed adequate by clinical criteria,7•9 but it has not been shown that adequate oxygenation can be achieved in humans. The mobile intensive care unit paramedics of Los Angeles County have been using an EOA routinely during prehospital cardiopulmonary resuscitation. Therefore, we had a unique opportunity to evaluate its effectiveness in an actual clinical setting.
rently only 25 to 65 percent of patients suffering ventricular fibrillation survive to reach a hospital, despite sophisticated systems of prehospital intensive care. l-4 Less than half of these patients are eventually discharged. Better resuscitative techniques and equipment are, therefore, constantly being developed for use by mobile rescue units. Adequate ventilation is a prerequisite for successful resuscitation; and simple, practical, and efficient means of providing adequate air exchange are necessary. Mouth-to-mouth, mouth-to-mask, or bagvalve-mask ventilation may be satisfactory, but each technique has significant drawbacks. 5 •6 Endotracheal intubation is, of course, preferred but requires skilled experienced personnel, proper positioning of the patient, and direct visualization of the glottis for orotracheal insertion of the tube. Don Michael and associates, 6 therefore, developed an esophageal occluding airway in an attempt to overcome these disadvantages. The esophageal obturator airway ( EOA) is a modification of their original "mouth-to-lung" airway. The EOA is simple to use, does not require a laryngoscope for insertion, and reduces the possibility of aspiration. °From the Receiving-Emergency Division and the Division of Cardiology, Department of Medicine, Harbor General Hospital, Torrance, Calif., and the School of Medicine, University of California, Los Angeles. • • Assistant Professor of Medicine. Manuscript received Mar 2]; revision accepted July 21. Reprint requests: Dr. Sclwfferman, Harbor General Hospital, TorTance, California 90509
CHEST, 69: 1, JANUARY, 1976
METIIODS
The EOA The EOA (Fig 1) resembles an endotracheal tube with the distal end occluded and 16 holes, each 3 mm in diameter, distributed over the section of the tube which will be positioned in the hypopharynx. The tube with face mask attached is passed into the esophagus blindly without need of a laryngoscope. The face mask is held tightly over the nose and mouth, the esophageal balloon is inflated, and ventilation is begun. Air or oxygen is blown into the open end of the tube, leaves the EOA through the small holes, and enters the trachea. The inflated esophageal balloon prevents the air from entering the stomach and also prevents vomiting. The mask prevents air from lealcing through nose or mouth. Therefore, the air must enter the trachea, which is the only unobstructed orifice ( Fig 2) . Proper positioning of the tube in the esophagus is assured if the rescuer hears adequate breath sounds and sees the chest wall rise and fall with each breath. Should the tube inadvertently be placed in the trachea, breath sounds would be absent, and the tube would be removed and reinserted. After the patient has been stabilized, and only when adequately trained personnel are at hand, the trachea should be intubated. Vomiting is common during removal of the EOA; and, therefore, it should not be removed until an
THE ESOPHAGEAL OBTURATOR AIRWAY 67
FIGURE
1. Esophageal obturator airway with syringe and face mask attached and balloon inflated.
endotracheal tube is in place with balloon inHated. Then the esophageal balloon can be deflated and the EOA removed. Study Population
Eighteen patients who were documented to have been in ventricular fibrillation or asystole at the time of arrival of mobile intensive-care-unit rescuers and who were transported to Harbor General Hospital, Torrance, Calif, were evaluated. Because patients are routinely taken to the nearest hospital after resuscitative attempts, the patients reported here form only a portion of the total community prehospital resuscitative attempts. Patients pronounced dead on arrival in the Emergency Department were not included nor were the few patients who were intubated before arterial blood could be drawn for analysis. Resuscitation and Study Procedure
All patients received primary care from highly trained mobile intensive care unit paramedics operating under the
radiotelemetric supervision of a physician or specially certified nurse at a base-station hospital.IO In each case, resuscitation in the field included basic life support plus advanced techniques which included electrical defibrillation and intravenous administration of drugs such as lidocaine, epinephrine, sodium bicarbonate, calcium chloride, and atropine. Prior to hospitalization, total ventilatory support was necessary in each patient, and the EOA was routinely used. Ventilation in the field was carried out with a portable demand valve system which delivered 100 percent oxygen. Resuscitation attempts were continued in the field until the patient was converted to a satisfactory stable rhythm or until the ventricular fibrillation or asystole was deemed refractory, in which case the patient was transported to the nearest hospital while receiving continuous cardiopulmonary resuscitation. At Harbor General Hospital, resuscitative efforts were continued by the Emergency Department's house officers and nurses plus a respiratory therapist. Frequent determinations of arterial blood gas values during cardiopulmo-
FIGURE 2. Schematic representation of EOA in proper position in patient. Air (thick arrow) blown into proximal end exits via small holes (thin arrows) and is forced down trachea, as other routes are occluded.
88 SCHOFFERMAN, OILL, LEWIS
CHEST, 69: 1, JANUARY, 1976
tal respiratory support at the time of evaluation.. The results of arterial blood gas analyses during ventilation with the EOA by a respiratory therapist in the Emergency Department are shown in Table 1. Twelve patients (group I ) had successfully undergone cardioversion to supraventricular rhythm in the field and no longer required external cardiac massage. Seven of these were being ventilated with IOO percent oxygen at the time of evaluation. The mean Pa02 in these seven patients was 268 mm Hg (range, I35 to 5IO mm Hg) . Four patients in group I received an FI02 of 0.4, and a mean Pa02 of 75 mm Hg was achieved (range, 56 to ll2 mm Hg). One patient was ventilated with room air, and the Pa02 was 8I mm Hg. The mean PaC 45 mm Hg). In addition, there was a general trend towards improvement in PaC~ after endotracheal intubation in both groups of patients. The explanation for the hypoventilation is not readily apparent. There was no evident clinical difference between the hypoventilated patients and those with normal or low PaC02. Every patient was apneic, and all required total ventilatory support. Tube mechanics might be implicated. Increased dead-space with the EOA compared to the endotracheal tube might contribute to the hypoventilation, as might unnoticed leaks around the face mask or around an underinHated esophageal balloon. A change in minute ventilation introduced by the rescuer in response to learning the initial arterial blood gas results may also have occurred. The majority of patients, however, including two patients still requiring external cardiac massage, had normal or low PaC02, demonstrating that it is very possible to achieve adequate PaC02. The data demonstrate that it is dif-
CHEST, 69: 1, JANUARY, 1976
ficult to predict accurately PaC02; and, therefore, it may be worthwhile to attempt to overventilate patients pending the availability of arterial blood gas results, as hypercapnia during cardiopulmonary resuscitation should be avoided. The results of this study are encouraging. The excellent oxygenation obtained in most patients implies that the EOA is a useful adjunct to cardiopulmonary resuscitation when endotracheal intubation is not feasible. The EOA might prove especially useful to volunteer rescue teams, to mobile intensive care unit personnel with small numbers of rescues, and to communities where large numbers of personnel must be trained. A 100 percent oxygen source is preferable, and frequent monitoring of arterial blood gas levels is desirable. ACKNOWLEDGMENTS: We would ll1c:e to thank Drs. Lucien Cuze and Eugene Nagel for their helpful review of the manuscript, Mrs. Jenny Keshishian for her valuable secretarial assistance, and the Harbor General Hospital's Emergency Department nurses and house staH who cared for these patients. REFERENCES
1 Liberthson RR, Nagel EL, Hirschman JC, et al : Pathophysiologic observations in prehospital ventricular fibrillation and sudden cardiac death. Circulation 49 :790-798, 1974 2 Adgey AA, Nelson PG, Scott ME, et al : Management of ventricular fibrillation outside hospital. Lancet 1:11691171, 1969 3 Crampton RS, Aldrich RF, Gascho JA, et al: Reduction of prehospital, ambulance and community coronarY death rates by the community-wide emergency cardiac care system. Am J Med 58: 151-165, 1975 4 Liberthson RR, Nagel EL, Hirschman JC, et al: Prehospital ventricular defibrillation : Prognosis and follow-up course. N Eng)] Med 291:317-321, 1974 5 Standards for cardiopulmonarY resuscitation (CPR) and emergency cardiac care ( ECC) . JAMA ( suppl) 227:833868, 1974 6 Don Michael T A, Lambert EH, Mehran A: "Mouth-tolung airway" for cardiac resuscitation. Lancet 2 : 1329, 1968 7 Don Michael TA, Gordon AS : Esophageal obturator airway : A new adjunct for artificial ventilation. Presented at the National Conference on Standards for Cardiopulmonary Resuscitation and Emergency Cardiac Care. Washington, DC, May 16, 1973 8 Farley M: The esophageal obturator airway. Respir Ther Nov/Dec, 1973 9 Smock SN: Esophageal obturator airway : Perferred CPR technique. J Am Coli Emergency Phys 4 :232-233, 1975 10 Lewis AJ, Ailshie G, Criley JM : Prehospital cardiac care in a paramedical mobile intensive care unit. Calif Med 117: 1-8, 1972 11 Greenbaum OM, Poggi J, Grace WJ: Communication to the editor. Chest 66:110, 1974 12 Greenbaum OM, Poggi J, Grace WJ : Esophageal obstruction during oxygen administration: A new method for use in resuscitation. Chest 65:188-191, 1974 13 Fillmore SJ, Shapiro M, Killip T : Serial blood gas studies during cardiopulmonary resuscitation. Ann Intern Med 72:465-469, 1970
THE ESOPHAGEAL OBTURATOR AIRWAY 71
