[Effects of anesthetic drugs and temperature on brain stem and mid-latency evoked potentials]

We evaluated the effects of anesthetic drugs and temperature on brain stem and mid-latency evoked potentials (BAEP and MLAEP) in 20-patients who were scheduled for elective cardiac operation using cardiopulmonary bypass with moderate hypothermia. At esophageal temperature of 36 degrees C, the latency of MLAEP was slightly prolonged by the increase of fentanyl dose, which suggested that the latency prolongation of MLAEP could not block the oscillation of auditory stimulation. At esophageal temperature of 27 degrees C, the latency of MLAEP nearly disappeared, and the latency of MLAEP gradually returned with the recovery of the esophageal temperature. The latency of BAEP was markedly prolonged at 27 degrees C and returned to the normal latency at 36 degrees C. The latency of MLAEP retained by high dose fentanyl suggests that patients may be aware during cardiopulmonary bypass at normothermia, and BAEP may be one of the useful brain function monitors during cardiopulmonary bypass.