Hypothermia and acid-base regulation in infants.

During progressive hypothermia for cardiac surgery, the need for advanced and comprehensive physiological monitoring systems is even more apparent and vital. A review of the literature on the physiological effects of hypothermia in animals reveals that the "physiological neutrality" intracellularly is achieved at progressively higher pH values as temperature falls, and that this more alkaline acid-base balance is apparently achieved while the total carbon dioxide content of the tissues remains at normothermic (normal body temperature) levels. Based on this, an anesthetic technique was studied, whereby the ventilation was maintained throughout the cooling/surgery/rewarming cycle at normothermic levels. This allowed a progressively more alkaline acid-base environment to be achieved. This technique is discussed in detail, together with information relating to the circulatory changes and complications seen and the degree of acid-base control obtained. The conclusion is drawn that the addition of carbon dioxide to the ventilation gases, of alternatively, a decrease in ventilation as temperature falls, is not only unnecessary, but perhaps also harmful.