Central sympathetic discharge and mean arterial pressure during halothane anaesthesia.

The effects of halothane on preganglionic cervical sympathetic activity and arterial pressure have been measured in intact and spinal cats, one dog and one baboon. The typical response was an early increase in sympathetic discharge as arterial pressure began to fall. Thereafter, although sympathetic activity declined progressively, at the time it regained the control level arterial pressure was already substantially reduced. At mean arterial pressures of 30-40 mm Hg pronounced increases in sympathetic activity occurred with little change in arterial pressure. Substitution of 70 per cent nitrous oxide for nitrogen during halothane administration usually increased the discharge rate. When halothane was discontinued, recovery of sympathetic discharge was slower than that of arterial pressure. In spinal cats, halothane significantly depressed preganglionic activity.