Neurologic dysfunction following cardiac operation with low-flow, low-pressure cardiopulmonary bypass

A prospective 6 month study of all patients undergoing cardiac operation with cardiopulmonary bypass (CPB) was undertaken to determine the incidence of neurologic and neuropsychological dysfunction following low-flow, low-pressure CPB. Among 204 patients who underwent cardiac operation with CPB, there were seven deaths (3.4%), six who developed new motor deficits (2.9%), and 35 (17.2%) who exhibited some neurologic or neuropsychological dysfunction at discharge. When compared to the 169 patients with no evidence of neurlogic or neuropsychological dysfunction at discharge, these 35 were older (65 +/- 10 versus 55 +/- 12 years), had a lower incidence of coronary artery bypass grafting as the sole surgical procedure (29% versus 55%), a higher mortality rate (11.4% versus 1.8%), and prolonged CPB (140 +/- 45 versus 107 +/- 38 minutes). The mean arterial pressure (MAP) during CPB was similar in the two groups (51 +/- 7 versus 49 +/- 7 torr), and an index of time at low pressure, torr x minutes below 50 (TM less than 50), was also similar in the two groups (589 +/- 591 versus 554 +/- 478 TM less than 50). The incidence of postoperative neurologic and neuropsychological complications appears comparable to that in reports from institutions employing high CPB flow and maintaining high CPB MAP. Our results suggest that CPB pressure, per se, is not the major determinant of postoperative neurologic and neuropsychological dysfunction.