Ectothermic philosophy of acid-base balance to prevent fibrillation during hypothermia.

In the ectotherms, or cold-blooded animals, carbon dioxide pressure decreases (PCO2) and pH increases as body temperature falls. This tends to increase coronary blood flow and prevent fibrillation. This concept was investigated in 181 consecutive patients undergoing open heart surgery of all types. In 121 cases, endothermic (warm-blooded) temperature-corrected normal values of pH, PCO2, and oxygen pressure were maintained during extracorporeal circulation as the perfusate temperature was lowered to 24 degrees C prior to aortic cross-clamping and administration of blood cardioplegia solution. In 49 patients (40%), ventricular fibrillation occurred prior to cross-clamping. In the other 60 consecutive cases, in which the ectothermic principle of cooling was applied, the PCO2 was allowed to decrease from 50 to 40 mm Hg and the non-temperature-corrected pH rose from 7.28 to 7.42. Fibrillation occurred in only 12 (20%) of these 60 patients.