Effect of nitrous oxide on myogenic motor evoked potentials during hypothermia in rabbits anaesthetized with ketamine/fentanyl/propofol

Background. A number of authors have reported that anaestheticssuppress myogenic motor evoked potentials (MEPs). However, theinfluence of hypothermia on these effects is unknown. Thereforewe investigated the effects of hypothermia on nitrous oxide-inducedsuppression of myogenic MEPs. Methods. Twenty-two rabbits anaesthetized with ketamine, fentanyland propofol were randomly allocated to one of three groups,with oesophageal temperatures of 40°C (n=8), 35°C (n=7)and 30°C (n=7). Myogenic MEPs in response to electricalstimulation of the motor cortex with a train of five pulseswere recorded from the soleus muscle. Following the controlrecording, nitrous oxide was administered at concentrationsof 30%, 50%, and 70% in random order, and MEPs were recorded.Control MEP amplitudes and percentage of control MEP amplitudes(%MEP amplitude) during the administration of nitrous oxidewere compared between the three groups. Results. Control MEP amplitudes were similar between the threegroups. Nitrous oxide suppressed MEPs in a dose-dependent mannerin all groups. During the administration of nitrous oxide, %MEP amplitudes at 35°C and 30°C (hypothermia) were significantlylower than those at 40°C (normothermia). Conclusion. These results suggest that nitrous oxide-inducedsuppression of MEPs may be augmented during hypothermia. Br J Anaesth 2002; 88: 836–40