Specific actions of halothane, isoflurane, and desflurane on sympathetic activity and A delta and C somatosympathetic reflexes recorded in renal nerves in dogs

Background: This was a study of the relative effects on directly recorded s ympathetic activity of desflurane, isoflurane, and halothane, Methods: Renal sympathetic nerve activity (RSNA) was recorded with bipolar electrodes in renal nerves exposed retroperitoneally In anesthetized (alpha -chloralose), paralyzed (succinylcholine), and artificially ventilated dogs . Somatosympathetic responses were evoked by supramaximal electrical stimul ation of radial nerves (0.33 Hz, 30 V, 0.5 ms), Spontaneous and evoked acti vity were rectified, averaged, and integrated to allow quantitative compari son of the effects of 3-12% desflurane, 0.6-2.4% isoflurane, and 0.4-1.6% h alothane. Results: Increasing concentrations of isoflurane progressively depressed me an RSNA, A delta, and C reflexes by 40% (P < 0.01), 50% (P < 0.01) and 70% (P < 0.001) respectively at 2.4% concentration Halothane depressed both ref lexes equally by approximately 60% (P < 0.01) at 1.6% concentration, withou t significant depression of spontaneous RSNA. Desflurane increased and subs equently decreased RSNA by 37% (P < 0.02) and 65% (P < 0.001) at concentrat ions of 6% and 12% respectively, and although somatosympathetic reflexes re mained unchanged up to 9%, both were depressed equally by 70% (P < 0.01) at 12% concentration, Conclusion: After equilibration, lower concentrations of desflurane remaine d excitatory, but,like isoflurane, higher concentrations depressed RSNA, Th e effect of halothane on RSNA was insignificant Isoflurane depressed C more than A delta somatosympathetic reflexes, which is uncorrelated with lipid solubility because desflurane and halothane, which have the highest and low est minimum alveolar concentration, respectively, depressed both equally.