[Suppressive effect of sevoflurane on somato-sympathetic reflexes in cats]

Effects of sevoflurane on the reflex activity of the sympathetic nervous system in cats were investigated by observing alteration of the amplitudes of somato-sympathetic medullary reflex potentials. These reflex potentials consist of two components, A- and C-reflex potentials, which are induced from the lumbar sympathetic trunk by electric stimulation of the ipsilateral femoral nerve. It is known that A- or C-reflex potential is induced by stimulating peripheral A-fiber group or C fiber group, respectively. Sevoflurane 1, 2 and 3% in oxygen for 30 minutes for each concentration by incremental fashion, were inhalated. Neither A nor C reflex potentials were suppressed by 1 and 2% sevoflurane but 3% sevoflurane caused a significant suppression of both reflex potentials in brain intact cats. Concentration-dependent suppression of C-reflex potentials and a tendency of concentration-dependent suppression of A-reflex potentials were observed in decerebrate cats. Mean arterial blood pressure showed a concentration-dependent decrease in both brain intact and decerebrate groups. These results indicate that sevoflurane with concentrations higher than 1 MAC (2.5% for cats) significantly suppresses somato-sympathetic reflex activities. The results suggest, however, that this agent with concentrations lower than 1 MAC suppresses the descending inhibitory system from supra-medullary centers so that the integrated sympathetic outflow from the medulla oblongata are not suppressed significantly. The results also suggest that direct depressive effect on the cardiovascular system by sevoflurane rather than through suppressive effect on sympathetic reflexes may play a major role in hypotension during inhalation of concentrations below 1 MAC.