Physiological studies on man with the pneumatic balance resuscitator, Burns model
Motley, H.L.; Cournand, A.
Journal of Aviation Medicine 17(5): 431-461
1946
ISSN/ISBN: 0095-991X PMID: 20273605 Document Number: 14067
1. The PBR was found to be a physiologically sound, small and compact device for giving effective artifi cial respiration when the subject was placed in the proper position and with a line pressure setting sufficient to give proper cycling of the device (20 to 30 cm. water). Improper cycling was indicated by chattering of the resuscitator, which indicated that there was no ventilation of the lungs. Proper cycling was a reliable and easily observed index that pulmonary ventilation was taking place. 2. The apneic individual should be in the supine position preferably, with the head hyper-extended on the cervical vertebrae. Supporting the jaw from below helped initiate proper cycling in cases where spontaneous breathing had stopped, and a slight Trendelenburg position favored expiration. The tongue did not cause trouble in cases where spontaneous breathing had ceased, nor was an airway tube necessary in order to secure pulmonary ventilation. 3. The resuscitator was simple to use, practically foolproof in operation, giving satisfactory service for long periods of time without special care, and there was no tendency for the PBR to clog with mucus or secretions even when used for extended periods of time. 4. The most difficult- clinical problem in the use of the PBR was securing a proper mask fit on the face without leaks, for the latter, if greater than 10 per cent, prevent the device from cycling. Even on carefully conducted tests on trained subjects (young men) a 5 per cent mask leak on an average was found. The army pressure demand mask (A13) fits young men well, but for general clinical use this mask was found unsatisfactory for giving intermittent positive pressure. 5. The PBR followed all types and rates of respirations studied very smoothly, especially on unconscious subjects. The average ratio of inspiration to expiration was 0.76. Subjectively the action was smooth and soft, lacking the harshness of the suck and blow type. The cycling rate decreased as the line pressure was increased. Satisfactory performance resulted when used on 100 per cent oxygen, compressed air and a helium-oxygen mixture, and the ventilation was increased approximately 49 per cent on the latter over 100 per cent oxygen. 6. On an average, S5 per cent of the line pressure was transmitted as peak pressure and 42 per cent as mean mask pressure. 7. Pulmonary ventilation was adequate in all types of cases when the PBR cycled properly. Some hyperventilation occurs at ground level, but at a simulated altitude of 25,000 feet this increase was much greater. When using a line pressure of 26 cm. water at 25,000 feet there was an immediate rise in minute ventilation from 9.82 to 16.98 liters per minute and at the end of one hour the arterial pCO2 fell from a normal value of 43.5 mm. Hg. to 25.7, with a corresponding change in pH from 7.41 to 7.57. Even after using the PBR at 25,000 feet on a high pressure setting, no evidence was observed of signs or symptoms occurring in acapnia. 8. Arterial blood pressure was maintained at an approximately normal level apparently by the increase in total peripheral vascular resistance, representing a compensatory mechanism for the reduced stroke volume. 9. Approximately 50 per cent of the mean mask pressure was transmitted to the right heart, and the reduction in cardiac output was proportional to the mean mask pressure. The mechanism of the decreased output of the heart involves a reduction in right ventricular pulse pressure. 10. On the basis of the observed figures for oxygen intake, there was an average decrease in cardiac output in the essentially normal cases of 22.1 per cent on the PBR, with a line pressure setting from 16 to 30 cm. water. However, when the above determinations were recalculated for probable mask leakage (at least 5 per cent) the decrease in cardiac output amounted to 13.9 per cent. In two studies at 25,000 feet the calculated cardiac output during PBR breathing showed a very significant reduction with a low line pressure setting. As the reduction in cardiac output was related chiefly to low oxygen intake, mask leakage seemed likely and when the figures were recalculated on the above basis the reduction was found to be probably not greater than 10 per cent. 11. In one case of extreme chronic anemia and in a second case after acute blood loss, there were no clinically significant deleterious effects on the dynamics of the circulation with low line pressures at ground level. 12. in two deep coma cases with cardiac failure and peripheral blood stagnation, the cyanosis became more marked with intermittent positive pressure on a low line pressure setting. On the basis of this limited experience, the use of intermittent positive pressure even on low line pressure settings appears to be contrα-indicated in conditions where there is no cardiac reserve, if spontaneous respirations are present. 13. The present study indicates that the PBR would be more efficient and more likely to succeed in p roviding adequate artificial respiration than most of the manual methods, when the device can be used without delay. The line pressure should be as low as is consistent with proper cycling so that the reduction in cardiac output will be minimal and yet provide adequate ventilation. As. soon as good spontaneous respirations have been initiated, 100 per cent oxygen should be used at ambient pressure.
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