W Tang, MH Weil, S Sun, D Kette, F Kette, RJ Gazmuri, F O'Connell and J Bisera
Institute of Critical Care Medicine, Palm Springs, CA 92262.

It is widely held that mechanical ventilation is essential for cardiopulmonary resuscitation (CPR). However, cardiac output and therefore pulmonary blood flow is reduced to less than one-third of normal during CPR. We therefore reasoned that ventilatory requirements are correspondingly reduced and postulated that gas exchange may be maintained during precordial compression with oxygen passively delivered to the airway in the absence of mechanical ventilation. After tracheal intubation, Sprague-Dawley rats were randomized. Fifteen animals were maintained on positive-pressure ventilation with room air and an additional 15 animals breathed spontaneously. Cardiac arrest was induced by electrical fibrillation. The inspired gas concentration of oxygen was then increased to 100% in both groups. Precordial compression was begun after 4 min of untreated ventricular fibrillation. After an additional 6 min of precordial compression, resuscitation was attempted by DC countershock. During cardiac resuscitation, there were no significant differences in coronary perfusion pressure between mechanically ventilated and spontaneously breathing animals, but arterial PO2 was significantly lower and arterial PCO2 was significantly higher in the absence of positive- pressure ventilation. However, neither resuscitability nor 24-h survival were affected. Postresuscitation myocardial contractility, reflected in the maximally generated dP/dt40, was also not adversely affected. In the unventilated group, only resuscitated animals developed spontaneous gaspings at an average frequency of 17 +/- 2/min- 1. The current emphasis on mechanical ventilation as the highest priority for cardiopulmonary resuscitation is therefore not fully supported under the experimental conditions of this study.

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