DIFFERENTIAL-EFFECTS OF NITROUS-OXIDE AND PROPOFOL ON MYOGENIC TRANSCRANIAL MOTOR EVOKED-RESPONSES DURING SUFENTANIL ANESTHESIA

We have compared the effects of 50% nitrous oxide and propofol, each a dministered concurrently with sufentanil, on the amplitudes and latenc ies of the compound muscle action potential (CMAP) response to transcr anial electrical stimulation. Using a crossover design, 12 patients un dergoing spinal surgery were exposed to both 50% nitrous oxide and pro pofol, the latter in a bolus-infusion regimen. Six patients received n itrous oxide first and six received propofol first. CMAP were recorded from the tibialis anterior muscle in response to both single and pair ed transcranial electrical stimuli. With single pulse stimulation, med ian CMAP amplitude was significantly greater during administration of nitrous oxide than propofol (nitrous oxide 335 (10th-90th percentiles 35-849) mu V; propofol 38 (0-251) mu V) (P<0.01). With paired stimulat ion, there was no significant difference in CMAP amplitude during the two regimens (nitrous oxide 1031 (296-1939) mu V; propofol 655 (0-1867 ) mu V). The results indicate that propofol caused more depression of transcranial electrical motor evoked responses than 50% nitrous oxide but that the difference was probably clinically unimportant when a pai red stimulation paradigm was used.