The influence of temperature on somatosensory-evoked potentials during cardiopulmonary bypass

Somatosensory-evoked potentials (SEPs) after median nerve stimulation were recorded in 10 neurologically normal patients during cardiopulmonary bypass and hypothermia. In all patients the changes of the latencies (spinal N13, cortical N20 and N35) and the central conduction time during cooling, and the decrease in latencies during rewarming was described by a gamma function. The analytic discussion of pooled data of all patients led to another SEP-latency-temperature relationship than the observation of each single patient. In 6 of 10 patients there was found a maximum of latency increase before the minimal temperature was reached. The cooling and the rewarming curve had to be considered separately. Latency changes of SEPs during hypothermia are discussed as a very complex phenomenon influenced by many technical and patient factors. This reduces the value of SEPs as an index of central nervous system integrity during open heart surgery and hypothermia.