Alpha-stat vs. pH-stat strategy during hypothermic cardiopulmonary bypass.

There are two different strategies of acid-base regulation during hypothermis. The alpha-stat strategy of ectotherms maintains the temperature-uncorrected arterial PCO2 and pH at normothermic values (i.e., 40 mmHg and 7.4, respectively), irrespective of the body temperature. In contrast, the pH-stat of hibernators maintains the temperature-corrected pH and PCO2 at the normal values at the different body temperatures. Clinically, it appears that it is more physiological to use the alpha-stat strategy whenever tepid or moderate hypothermic CPB is used in order to maintain intracellular electrochemical neutrality, and to adopt the pH-stat strategy whenever deep hypothermic circulatory arrest is induced, in order to otimize brain protection.