Hyperperfusion and cerebral dysfunction. Effect of differing acid-base management during cardiopulmonary bypass.

Alterations in cerebral blood flow (CBF) occurring during cardiopulmonary bypass (CPB), which are thought to be responsible for increased morbidity, are probably related to changes in arterial carbon dioxide during acid-base management. In this study, 70 patients undergoing elective coronary artery bypass surgery (CABS) were randomised to one of two differing, but widely practised, cardiopulmonary bypass acid-base protocols; pH-stat and alpha-stat. Cerebral blood flow was measured during surgery using the xenon-133 isotope clearance technique. Cerebral oxygen metabolism was measured as the cerebral metabolic rate for oxygen (CMRO2) and matching of the cerebral blood flow to oxygen demand as the cerebral extraction ratio for oxygen (CERO2). Detailed neuropsychological tests were conducted in all patients before surgery and repeated at 6 weeks after surgery for assessment of changes in cognitive function. During hypothermic (28 degrees C) CPB, CBF was significantly greater (P < 0.001) in the pH-stat group (41 ml/100 g per min; 95% confidence intervals (CI), 39-43) than in the alpha-stat group (24 ml/100 g per min; 95% CI, 22-26). The cerebral extraction ratio for oxygen indicated a degree of mismatch of cerebral perfusion and demand during CPB in both pH-stat and alpha-stat groups (0.12; 95% CI, 0.11-0.14 and 0.25; 95% CI, 0.22-0.28, respectively). This mismatch was far more pronounced in the pH-stat group than in the alpha-stat group, indicating greater disruption in cerebral autoregulation in the former group.(ABSTRACT TRUNCATED AT 250 WORDS)