The experimental studies on the beneficial effect of the various levels of hypothermia during complete cardiopulmonary bypass have been stressed by previous reports from this laboratory.1 Profound hypothermia was found to permit 60 minutes of circulatory arrest in the dog with a survival rate of 78%.2 This was similar or better than the survival from comparable periods of normothermic perfusion as reported by others.3-5 The following study was devised to see whether or not two hours of profound hypothermia would be tolerated, while perfusion was maintained with a pump oxygenator.
Experimental Design: Dogs used in this study were divided into two groups: (1) a control normothermic group (12 dogs) using closed chest partial cardiopulmonary bypass of 200 minutes, (2) a deep hypothermic group (esophageal temperature below 10 C) using 200 minutes of perfusion, including 120 minutes of perfusion below 10 C. The group 2 was further divided