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TECHNOLOGY, COMPUTING, AND SIMULATION

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

Department of Anesthesiology, Nara Medical University, Japan

Address corresponding and reprint requests to Takanori Sakamoto, MD, Department of Anesthesiology, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634–8522, Japan. Address e-mail to tsakamot{at}naramed-u.ac.jp

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°C of esophageal temperature, the rabbits were cooled by surface cooling. Esophageal temperature was maintained at 35°C, 32°C, 30°C, and 28°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°C compared with the control value at 38°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°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.

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