Tolerance of Puppies to Circulatory Arrest During Surface Induced Hypothermia

摘要

Studies were made of the tolerance of 64 puppies (5-10 weeks old, weighing 1.5-3 kg) to varying periods of circulatory arrest when cooled to 16 - 18C. Anesthesia was induced with intravenous injection of sodium pentothal; puppies were then intubated and a mechanical respirator attached using a tidal volume of 44 cc/kg and a rate of 18 per minute. The right femoral artery was cannulated for recording blood pressure and taking blood samples. Cooling was induced by immersion in ice. A bilateral anterior thoracotomy permitted inflow occlusion by clamping of both cavae and ligation of the azygos vein. After periods of circulatory arrest, the venae cavae were released and rewarming accomplished by irrigating the chest cavity with 40C normal saline solution, and by external means, until esophageal temperature reached 37C. Control thoracotomy dogs showed 80% survival after bilateral thoracotomy. Eucapnic dogs showed 39% survival after 20-40 minutes inflow occlusion. Most common cause of death was circulatory collapse which appeared on rewarming when esophageal temperature reached 27 - 30C. Hypercapnic dogs, ventilated with 5% CO2 and 95% O2 gas mixture had survival rate of 78% (14/18). It was possible to induce the revert hypothermia in puppies 6-8 weeks old without pdifficulty. Key to the technique is first warming the heart through the open chest, which permits equitable distribution of warm blood by a forceful warm heart. The time limit set by use of immersion cooling for circulatory arrest in small subjects is still not sufficient to permit complicated intracardiac surgical procedures. (Author)