Background and objective Despite the fact that both general anaesthetics and hypotensive drugs influence autonomic nervous activity, no study has yet examined the heart rate variability during deliberate hypotension and general anaesthesia. The aim of this was to clarify the heart rate variability changes during deliberate hypotension under sevoflurane–nitrous oxide anaesthesia.

Methods Autonomic nervous system activity in patients (n = 45) subjected to deliberate hypotension during sevoflurane in nitrous oxide and oxygen anaesthesia was investigated by a heart rate variability measurement. Three different types of hypotensive drugs, a calcium channel antagonist (nicardipine), a nitric oxide donor (nitroglycerin) and a vasodilatory prostaglandin (alprostadil), were used to induce hypotension.

Results In all groups, low frequency power (sympathetic and parasympathetic indicator) and the ratio of low frequency to high frequency power (the LF/HF ratio, sympathetic indicator) were suppressed by induction of anaesthesia. In the control group, preanaesthesia low frequency power was 195 ± 139 ms2, the LF/HF ratio 10.3 ± 5.7, during anaesthesia 5 ± 9 ms2, 0.6 ± 0.8, respectively, P = 0.0093, 0.0034, whereas high frequency power (parasympathetic indicator) was not significantly changed. In those patients receiving nicardipine or nitroglycerin during anaesthesia, these variables did not differ significantly from those in the control group. During prostaglandin E1 infusion, high frequency power was higher compared with the values in the other groups (17 ± 12 ms2 in the prostaglandin group, 7 ± 6 ms2 in the nicardipine group, 6 ± 5 ms2 in the nitroglycerin group and 6 ± 4 ms2 in the control group, respectively, P = 0.0326, 0.0251, 0.0197).

Conclusions Sevoflurane in nitrous oxide and oxygen anaesthesia reduces sympathetic autonomic activity considerably, and the expected increases caused by hypotensive agents that occur in awake volunteers were not seen.