Renin-angiotensin-aldosterone system and plasma vasopressin in surgical patients anaesthetized with halothane or isoflurane.

The effects of halothane and isoflurane anaesthesia on plasma renin activity and plasma concentrations of aldosterone and vasopressin were investigated in 20 cholecystectomy patients. Plasma renin activity rose significantly during both halothane and isoflurane anaesthesia without surgery, and increased further after the commencement of operation. Plasma aldosterone increased slightly during halothane and isoflurane anaesthesia, but the highest concentrations, three times the control values, were measured during surgery in both groups. Plasma vasopressin decreased during halothane and isoflurane anaesthesia to half of the control values, but rose significantly during cholecystectomy. During anaesthesia and surgery there were no significant differences in the mean arterial pressures of the groups. The results demonstrate that isoflurane stimulates the renin-angiotensin system to a similar extent as halothane, although it causes hypotension by a different mechanism. The activation of the renin-angiotensin-aldosterone system may be an essential compensatory mechanism, which antagonizes the decrease of blood pressure. Plasma vasopressin probably has no role in regulating blood pressure during anaesthesia.