Median nerve somatosensory evoked potentials were recorded in 21 patients undergoing cardiac surgical procedures utilizing cardiopulmonary bypass, in order to establish the effects of hypothermia, reductions in mean arterial pressure, and alterations in cardiopulmonary bypass flows on evoked potential latency. Induction and maintenance of anesthesia with fentanyl caused a significant prolongation of latency of the first cortical peak. Temperature changes were linearly correlated with changes in latency for peaks recorded from Erb's point (r = -0.843, p less than 0.01) and the contralateral cortex (r = 0.843, p less than 0.01). There was no significant effect of mean arterial pressure or cardiopulmonary bypass flow reductions on latencies under the conditions of this study. Our results emphasize the importance of monitoring peripheral and first cortical peak latencies in evaluating somatosensory evoked potentials. It is suggested that peak latency prolongations beyond those predicted by temperature alterations may be indicative of hypoperfusion.

1 In a placebo-controlled, double-blind, randomized, parallel group study one hundred and one patients with supine diastolic blood pressure -100 mm Hg phase V, despite treatment with atenolol 100 mg plus chlorthalidone 25 mg once daily also received either felodipine 5-20 mg twice daily or hydralazine 25-100 mg twice daily for 6 weeks. 2 Felodipine achieved a lower supine blood pressure (mean + s.d. 177/108 + 29/8-138/82 ± 19/8 mm Hg) than hydralazine (174/109 + 25/8-149/92 + 26/11 mm Hg), (P < 0.05/P < 0.001). Felodipine also lowered supine diastolic blood pressure to < 90 mm Hg more often than hydralazine (42 vs 22 patients, P < 0.001). 3 The incidence of unwanted effects was similar in both groups. The felodipine treated patients experienced more ankle swelling and flushing than those in the hydralazine group who experienced more headache and minor gastro-intestinal upset.