[The evaluation of cerebral oxygen balance during moderate hypothermic cardiopulmonary bypass]

The aim of this study was to evaluate cerebral oxygen balance during moderate hypothermic cardiopulmonary bypass (CPB). We measured jugular bulb venous oxygen saturation (SjO2), oxygen extraction ratio (O2 ER), glucose extraction ratio (Glu ER), and lactate production ratio (Lac PR) in 20 adult patients undergoing cardiac surgery. Fentanyl and midazolam anesthesia, alpha-stat blood gas management, non-pulsatile flow of 2.0-2.4 l.min-1.m-2, and moderate hypothermia were used in all cases. During cooling (at 34 degrees C of nasopharyngeal temperature), jugular-arterial blood difference of carbon dioxide partial pressure and O2 ER decreased, and SjO2 increased significantly. On the other hand, O2 ER increased, and SjO2 decreased significantly during rewarming (at 34 degrees C). There were no significant changes in oxygen-glucose index, lactate-glucose index, lactate-oxygen index, lactate production ratio, and lactate-pyruvate ratio. Ten (50 %) of 20 patients who met reduced saturation criteria (defined as SjO2 < 55 %), showed significantly higher O2 ER and lower SjO2 than the non-reduced saturation group from postinduction to rewarming period. We conclude that cerebral venous reduced saturation represents a global imbalance in cerebral oxygen supply-demand-utility that may occur during rewarming period, and that the reduced saturation group represents a significant difference in cerebral oxygen balance during even stable hypothermic CPB. These episodes, however, are not associated with the acceleration of anaerobic glycolysis.