MYOCARDIAL HYPERCARBIC ACIDOSIS REDUCES CARDIAC RESUSCITABILITY

Background. The severity of spontaneous myocardial hypercarbic acidosis during cardiac-arrest previously has been predictive of the likelihood of restoring spontaneous circulation. The present study investigated whether hypercarbia itself impairs cardiac resuscitation. Since coronary perfusion pressure is the overriding determinant of cardiac resuscitability, we used a porcine model of cardiac arrest in which coronary perfusion pressure was controlled. Methods: In 31 domestic pigs anesthetized with pentobarbital, the lungs were mechanically ventilated. Myocardial carbon dioxide tension and hydrogen ion concentration were measured by sensors advanced into the myocardium. After 15 min of untreated ventricular fibrillation, venoarterial extracorporeal circulation was initiated. Animals were randomized to receive a carbon dioxide gas fraction in the extracorporeal perfusate of 0.00, 0.10, 0.30, or 0.50 with oxygen concentration maintained constant at 0.50. Extracorporeal flow was adjusted to maintain a coronary perfusion pressure in the range of 60-80 mmHg, a level of predictive resuscitability. Results: The proportion of animals successfully resuscitated and the proportion of animals maintaining spontaneous circulation for 60 min or longer decreased with increasing perfusate P(CO2) and concurrent increases in myocardial CO2 tension in the absence of altered oxygen utilization (P < .01). Conclusions. Hypercarbia, in this experimental setting, was therefore a quantitative determinant of both myocardial resuscitability and the restoration of spontaneous circulation.