CARDIOPULMONARY-RESUSCITATION BY PRECORDIAL COMPRESSION BUT WITHOUT MECHANICAL VENTILATION

It is widely held that mechanical ventilation is essential for cardiop ulmonary resuscitation (CPR). However, cardiac output and therefore pu lmonary blood flow is reduced to less than one-third of normal during CPR. We therefore reasoned that ventilatory requirements are correspon dingly reduced and postulated that gas exchange may be maintained duri ng precordial compression with oxygen passively delivered to the airwa y in the absence of mechanical ventilation. Af ter tracheal intubation , Sprague-Dawley rats were randomized. Fifteen animals were maintained on positive-pressure ventilation with room air and an additional 15 a nimals breathed spontaneously. Cardiac arrest was induced by electrica l fibrillation. The inspired gas concentration of oxygen was then incr eased 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 countersh ock. During cardiac resuscitation, there were no significant differenc es in coronary perfusion pressure between mechanically ventilated and spontaneously breathing animals, but arterial PO2 was significantly lo wer and arterial PCO2 was significantly higher in the absence of posit ive-pressure ventilation. However, neither resuscitability nor 24-h su rvival were affected. Postresuscitation myocardial contractility, refl ected in the maximally generated dP/dt(40), was also not adversely aff ected. 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.