Suppressive effect of nitrous oxide on motor evoked potentials can be reversed by train stimulation in rabbits under ketamine/fentanyl anaesthesia, but not with additional propofol

The effect of nitrous oxide on myogenic motor evoked potentials(MEPs) after multipulse stimulation is controversial. We investigatedthe effects of propofol in this paradigm. MEPs were elicitedelectrically by a single pulse and by trains of three and fivepulses in rabbits anaesthetized with ketamine and fentanyl.Nitrous oxide 30–70% was given and MEPs were recorded.After washout of nitrous oxide, propofol was given as a bolusof 10 mg kg^–1 followed by 0.8 (n=9) or 1.6 mg kg^–1 min^–1(n=8) as a continuous infusion. Nitrous oxide was then readministeredand MEPs were recorded. Without propofol, nitrous oxide significantlyreduced the amplitude of MEPs dose-dependently, but this effectwas reversed by multipulse stimulation. Administration of low-dosepropofol enhanced nitrous oxide-induced suppression, and thiseffect was reversed by five-pulse stimulation. However, high-dosepropofol produced a greater increase in suppression, such thateven five-pulse stimulation did not overcome the suppression.The results suggest that the degree of reversal of nitrous oxide-inducedMEP suppression produced by multipulse stimulation is affectedby the administration of propofol. Br J Anaesth 2001; 86: 395–402