Enhancement of somatosensory evoked potentials by etomidate in cats: an investigation of its site of action.

Enhancement of somatosensory evoked potentials by etomidate has been reported in recent clinical studies. This investigation was designed to investigate the central nervous system site of action responsible for this effect. Six adult cats were anesthetized with halothane (0.8-1%) in a mixture of 50% N2O in O2. A recording electrode was placed stereotactically in the ventral posterior lateral nucleus of thalamus (VPL), and a ball electrode was placed over the surface of the hind limb region of primary sensory cortex. Somatosensory evoked potentials in response to stimulation of tibial nerve thus were simultaneously recorded from cerebral cortex and VPL. The effect of two doses (1 and 3 mg.kg-1) of etomidate given 2 h apart on the latency and amplitude of cortical (positive wave at 15 ms) and thalamic (positive deflection at 10 ms, followed by negative deflection at 17 ms) evoked potentials was studied. There was no significant effect of etomidate on either latency or amplitude of early, positive thalamic potentials. Both doses of etomidate caused a significant increase in the latency and amplitude of cortical potentials. The mean latency of cortical potential increased by 1.72 ms (11%) after the 1 mg.kg-1 dose and 2.3 ms (15.9%) after the 3 mg.kg-1 dose. The maximum mean increase in the amplitude of cortical potentials was 14.3 microV (mean increase 78%, range 28-241%) after 1 mg.kg-1 and 19.1 microV (mean increase 112%, range 28-202%) after 3 mg.kg-1. Cortical amplitude remained significantly elevated for 30 min after 1 mg.kg-1 and for the remainder of the study period (60 min) after 3 mg.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)