Effect of sevoflurane on spontaneous sympathetic activity and baroreflexes in rabbits.

Sevoflurane causes a decrease in mean arterial pressure (MAP). We have studied in anaesthetized rabbits its interactive effects on MAP, the autonomic nervous system and baroreflexes. During sevoflurane administration changes in renal sympathetic nerve activity (RSNA) and heart rate (HR) were observed: (1) when the normal decrease in MAP occurred; (2) when this was prevented by angiotensin II; (3) during a similar decrease in MAP induced by infusion of sodium nitroprusside (SNP) without sevoflurane administration; and (4) during pressor and depressor responses to phenylephrine and SNP. There was a reduction in MAP from 80 to 40 mm Hg after 1-4% sevoflurane without changes in HR, while RSNA remained unchanged only up to concentrations of 3% and was depressed by 37% (P < 0.05) with 4% sevoflurane. When MAP was maintained constant with angiotensin II, both HR and RSNA decreased, by 12% and 69%, respectively, after 4% sevoflurane (P < 0.05). A decrease in MAP of 40 mm Hg during infusion of SNP increased HR and RSNA by 22% (P < 0.05) and 150% (P < 0.01), respectively. At 2% sevoflurane, baroreflex sensitivity (i.e. delta RSNA/delta MAP and delta HR/delta MAP) was depressed by 36% and 57%, respectively, for the pressor effects of pherylephrine, and by 89% and 81%, respectively, for the depressor effects of SNP. We conclude that the baroreflexes continued to compensate for the effects of sevoflurane on sympathetic and cardiomotor activity with concentrations up to 3% and 4%, respectively.