The use of VEPs for CNS monitoring during continuous cardiopulmonary bypass and circulatory arrest.

Cerebral function was monitored with the use of visual evoked potentials (VEPs) in 16 infants (mean age 9.9 +/- 4.3 months) during surgery for congenital cardiac anomalies. While hypothermia was employed in all patients, half (8) remained on continuous cardiopulmonary bypass (CCB) while the rest were cooled to lower temperatures before the induction of circulatory stasis and venous exsanguination (CA), i.e., profound hypothermic circulatory arrest (PHCA). VEPs were recorded before, during and after surgical intervention. Latency changes occurred in both the N100 and P145 components of the VEP as a function of systemic temperature during cooling in both groups. Differences in the VEPs were found between the two groups post-operatively, with the most interesting result being a greater increase in P145 latency in the CA group after rewarming. To the extent that VEPs reflect neurological status, our findings suggested that CCB was associated with less perturbation in acute neurological status than PHCA, and shorter arrest times and lower temperatures during CA were associated with the most favourable post-operative VEPs. Hence, intraoperative monitoring of VEPs appeared to be useful as an objective measure of the short-term effects of various cardiopulmonary procedures on neurophysiological function.