The stress response to induced hypotension for cerebral aneurysm surgery: a comparison of two hypotensive techniques.

Plasma epinephrine (PE), plasma norepinephrine (PNE), plasma renin activity (PRA), mean arterial pressure (MAP) and heart rate (HR) were measured before, during and after induced hypotension in two groups of patients undergoing cerebral aneurysm surgery. In Group I isoflurane was used to maintain anaesthesia and induce hypotension. Mean PE fell significantly during hypotension and remained reduced after hypotension, mean PNE remained unchanged, while mean PRA rose slightly but not significantly during hypotension, falling again after hypotension. In Group II halothane was used to maintain anaesthesia and sodium nitroprusside to induce hypotension. During anaesthesia and surgical stimulation PNE and PRA were significantly greater compared to Group I. Mean PE, PNE and PRA all rose during hypotension and remained elevated after hypotension. The rise in PNE and PRA was statistically significant. After hypotension the MAP in Group II was significantly higher when compared to Group I. There was no significant change in HR during the study in either group. In conclusion, isoflurane-induced hypotension with isoflurane anaesthesia unlike sodium nitroprusside-induced hypotension with halothane anaesthesia attenuated the stress response.