ANALGESIC EFFECT IN HUMANS OF SUBANAESTHETIC ISOFLURANE CONCENTRATIONS EVALUATED BY EVOKED-POTENTIALS

The aim of this study was to see if an analgesic effect of subanaesthe tic concentrations of isoflurane could be detected with evoked potenti als elicited by nociceptive stimuli. We studied 10 healthy volunteers breathing three steady-state subanaesthetic concentrations of isoflura ne (0.08, 0.16 and 0.24 vol% end-tidal). Reaction time, subjective pai n intensities and evoked vertex potentials to laser (LEP) and electric al (SEP) stimuli were recorded and compared with auditory evoked poten tials (AEP). Compared with baseline, the subanaesthetic concentrations of isoflurane did not change the latencies of the evoked potentials, but caused a significant reduction in the amplitudes of the LEP and SE P at 0.16 and 0.24 vol% and of the AEP at all three concentrations. Th ere were no changes in perceived pain intensity, and isoflurane produc ed similar reductions in evoked potentials elicited by both nociceptiv e and non-nociceptive stimuli. The reaction time was increased signifi cantly at 0.24 vol% isoflurane. The results demonstrated that subanaes thetic isoflurane concentrations caused similar changes in evoked pote ntials with both painful and non-painful stimuli, with no effect on pe rceived pain intensity.