The effect of hypothermia on myogenic motor-evoked potentials to electrical stimulation with a single pulse and a train of pulses under propofol/ketamine/fentanyl anesthesia in rabbits

In the present study, we investigated the effect of hypothermia on myogenic motor-evoked potentials (MEPs) in rabbits. The influence of stimulation paradigms to induce MEPs was evaluated. Twelve rabbits anesthetized with ketamine, fentanyl, and propofol were used for the study. Myogenic MEPs in response to electrical stimulation of the motor cortex with a single pulse and a train of three and five pulses were recorded from the soleus muscle. After the control recording of MEPs at 38 degrees C of esophageal temperature, the rabbits were cooled by surface cooling. Esophageal temperature was maintained at 35 degrees C, 32 degrees C, 30 degrees C, and 28 degrees C, and MEPs were recorded at each point. MEP amplitude to single- pulse stimulation was significantly reduced with a re-duction of core temperature to 28 degrees C compared with the control value at 38 degrees C (0.8 +/- 0.4 mV versus 2.3 +/- 0.3 mV; P < 0.05), whereas MEP amplitude to train-pulse stimulation did not change significantly during the cooling. MEP latency was increased linearly with a reduction of core temperature regardless of stimulation paradigms. In conclusion, these results indicate that a reduction of core temperature to 28 degrees C did not influence MEP amplitudes as long as a train of pulses, but not a single pulse, was used for stimulation in rabbits under propofol/ketamine/fentanyl anesthesia. IMPLICATIONS: Intraoperative monitoring of myogenic motor-evoked potentials (MEPs) may be required under hypothermic conditions because of its neuroprotective efficacy. However, data on the influence of hypothermia on myogenic MEPs are limited. The results indicate that multipulse stimulation may be better than single-pulse stimulation when monitoring MEPs during hypothermia.