MIDLATENCY AUDITORY-EVOKED POTENTIALS IN HUMANS DURING ANESTHESIA WITH S(- A DOUBLE-BLIND, RANDOMIZED COMPARISON WITH RACEMIC KETAMINE() KETAMINE )

Mid-latency auditory evoked potentials (MLAEP) reflect the primary cor tical processing of auditory stimuli. They are suppressed widely durin g general anesthesia. Under ketamine, in contrast, MLAEP seem to be pr eserved. Ketamine exists in two optical isomers, S(+)ketamine and R(-) ketamine, which differ in their pharmocodynamic properties. S(+)ketami ne has a higher anesthetic-hypnotic and analgesic potency than R(-)ket amine or the racemic mixture of S(+)ketamine and R(-)ketamine. In a bl inded, randomized evaluation we compared the effect of induction of ge neral anesthesia with the more potent ketamine compound-S(+)ketamine-t o induction with the racemic ketamine on MLAEP in 60 patients schedule d for minor gynecologic procedures. Anesthesia was induced with S(+)ke tamine (1 mg/kg Group I, n = 30) or an equianesthetic dose of racemic ketamine (2 mg/ kg, Group II, n = 30). Auditory evoked potentials (AEP ) were recorded before, during, and after induction of general anesthe sia. Latencies of the peaks V, Na, Pa, Nb, and P1 and amplitudes Na/Pa , Pa/Nb, and Nb/P1 were measured. A fast-Fourier transform was used to calculate the power spectra of the AEP. The baseline MLAEP peaks of t he awake patients were of normal amplitude and demonstrated a characte ristic periodic wave form morphology. Power spectra indicated high ene rgy in the 30-40 Hz frequency range. After induction of general anesth esia with S(+)ketamine or racemic ketamine, there was no increase in l atencies of peaks V, Na, Pa, Nb, or P1. No decrease in amplitudes Na/P a, Pa/Nb, or Nb/P1 could be observed. There was no significant change in the power spectra. MLAEP do not change in amplitude or latency duri ng induction of general anesthesia with S(+)ketamine or racemic ketami ne. Primary cortical processing of auditory stimuli seems to be preser ved under S(+)ketamine and racemic ketamine.