The Effect of Temperature, Mean Arterial Pressure, and Cardiopulmonary Bypass Flows on Somatosensory Evoked Potential Latency in Man

Abstract

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.

AAEM minimonograph #14: The influence of temperature in clinical neurophysiology

“…In another study from the same laboratory, central conduction times were reported to increase 6.6%/"C decrease in t e m p e r a t~r e .~~ Fairly linear increases in absolute latencies of posterior tibia1 SEPs (popliteal fossa, lumbar spinal cord, and cortex) were reported with hypothermia down to 25OC-28"C by others as well. 30 In one study, larger than 1.5 m/"C increases in the latency to the first positive cortical peak was considered reason for concern and intervention.lo4 Nasopharyngeal temperatures were found to correlate well with the observed changes, but not rectal or limb temperatures. Amplitude changes of scalp SEPs in hypothermia do not correlate well with temperature, yet they are usually reduced lo4; this is most likely the result of desynchronization in the afferent central pathways similar to that observed in peripheral nerves.…”