Posthypothermic Circulatory Failure I. Physiologic Observations on the Circulation

Certain aspects of cardiovascular function were studied in dogs that were cooled to 30 C. without ventilatory assistance, and rapidly rewarmed in warm water. WAhile in the hypothermic state, the animals appeared to make an adequate cardiovascular adjustment to the lowered body tempera-ture. Upon rewarming, however, each animal incurred an acute circulatory collapse, which was characterized by a low cardiac output, diminished ventricular work, hypotension, hyperpnea, and increased arteriovenous oxygen difference. It is uncertain whether this circulatory failure is central or peripheral in origin. FOLLOWING experimental hypothermia in the dog cooled to temperatures as low as 20 C., the animal will return to a normal physiologic state upon rewarming.1-7 The deaths that did occur were categorized into essentially 3 groups: (1) ventricular fibrillation or cardiac asystole, (2) circulatory collapse, and (3) respiratory collapse. On the other hand, some animals were not normal physiologically for some time after re-warming even if they survived. Bigelow ' found a low cardiac output in 1 animal for one hour following rewarming. Reduced cardiac output has also been shown by Prec and co-workers,9 by Ross,'0 and by Sabiston and associates."' The present report concerns the cardio-vascular status of the dog cooled to the mod-erate level of 30 C. and rapidly rewarmed. It has been found that the animal rapidly re-warmed develops acute circulatory failure, which persists for at least three hours. METHOD Apparently healthy mongrel dogs in the weight range of 12 to 38 Kg. were used. The experiments were done from October 1954, through April 1955