Can hypocapnia reduce cerebral embolization during cardiopulmonary bypass?

Background. Cerebral embolization is a major cause of central nervous dysfu nction after cardiopulmonary bypass. Experimental studies demonstrate that reductions in arterial carbon dioxide tension (PaCO2) can reduce cerebral e mbolization during cardiopulmonary bypass. This study examined the effects of brief PaCO2 manipulations on cerebral embolization in patients undergoin g cardiac valve procedures. Methods. Patients were prospectively randomized to either hypocapnia (PaCO2 = 30 to 32 mm Hg, n = 30) or normocapnia (PaCO2 = 40 to 42 min Hg, n = 31) before aortic cross-clamp removal. With removal of the aortic cross-clamp embolic signals were recorded by transcranial Doppler ultrasonography for t he next 15 minutes. Results. Despite significant differences in PaCO2, groups did not differ st atistically in total cerebral emboli counts. The mean number of embolic eve nts was 107 +/- 100 (median, 80) in the hypocapnic group and 135 +/- 115 (m edian, 96) in the normocapnic group, respectively (p = 0.315). Conclusions. Due to the high between-patient variability in embolization, r eductions in PaCO2 did not result in a statistically significant decrease i n cerebral emboli. In contrast to experimental studies, the beneficial effe ct of hypocapnia on cerebral embolization could not be demonstrated in huma ns. (C) 2001 by The Society of Thoracic Surgeons.