CARDIOPULMONARY BYPASS - PERIOPERATIVE CEREBRAL BLOOD-FLOW AND POSTOPERATIVE COGNITIVE DEFICIT

Increased cerebral blood flow occurring during cardiopulmonary bypass as a result of changes in arterial carbon dioxide tension during acid- base regulation is thought to increase postoperative cognitive dysfunc tion. We studied 70 patients undergoing coronary artery bypass procedu res who were randomized to two different acid-base protocols: pH-stat or alpha-stat regulation. Cerebral blood flow cerebral blood now veloc ity, and cerebral oxygen metabolism were measured before bypass, durin g bypass (hypothermic [28 degrees C] and normothermic phases), and aft er bypass. Detailed cognitive tests were conducted before operation an d 6 weeks after operation. During 28 degrees C bypass, cerebral blood now was significantly (p < 0.05) higher in the pH-stat group than in t he alpha-stat group (41 +/- 2 versus 24 +/- 2 mL . 100 g(-1). min(-1)) , and cerebral blood now velocity was significantly increased in the p H-stat group and significantly decreased in the alpha-stat group (152% +/- 10% versus 78% +/- 7%). Cerebral extraction ratio of oxygen demon strated a relatively greater disruption of autoregulation in the pH-st at group than in the alpha-stat group with relative hyperemia of 0.12 +/- 0.02 versus 0.26 +/- 0.03, respectively, during 28 degrees C bypas s. Using the criterion of deterioration in three or more neuropsycholo gic tests, a significantly higher proportion of patients in the pH-sta t group fared less well than in the alpha-stat group (49% +/- 17% vers us 20% +/- 13%). Patients in the alpha-stat group experienced less dis ruption of cerebral autoregulation during hypothermic cardiopulmonary bypass, and this was accompanied by a reduction in postoperative cogni tive dysfunction.