Crystalloid hemodilution, hypothermia, and halothane blood solubility during cardiopulmonary bypass

Sequential determinations of halothane blood solubility were determined in 8 patients undergoing cardiac surgical procedures with cardiopulmonary bypass (CPB), hypothermia, and crystalloid hemodilution. The mean temperature-corrected blood/gas partition coefficient (B/G) at the end of surgery (2.4) was lower than preceding induction (2.7). The greatest mean B/G (2.9) occurred after induction of anesthesia. The halothane B/G did not increase significantly at the inception of CPB but decreased from a mean 2.7 to 1.6 as the patients were rewarmed. The maximum range of B/G for a single patient was 1.4 to 3.1. For halothane, the increased blood solubility due to hypothermia was initially antagonized by the crystalloid hemodilution. This antagonism would also be anticipated for methoxyflurane, enflurane, and isoflurane. For N2O and diethyl ether, the increased blood solubility due to hypothermia would be unopposed by simultaneous crystalloid hemodilution.