Plasma renin, catecholamines, vasopressin and aldosterone during hypotension induced by labetalol with isoflurane.

Deliberate hypotension may induce secretion of stress hormones. In the present study, the effects of hypotension induced by labetalol with isoflurane or plasma renin activity, plasma concentrations of adrenaline, noradrenaline, vasopressin, and aldosterone were investigated in eight adult patients undergoing middle-ear surgery. The mean arterial pressure was 50 mmHg (6.7 kPa) during hypotension. Plasma renin activity rose significantly during anaesthesia before hypotension, being similar during hypotension and before hypotension, and in returned postoperatively to the initial level. Plasma adrenaline fell significantly during hypotension and rose after anaesthesia to the preanaesthetic level. Plasma noradrenaline rose slightly during hypotension and after anaesthesia, but not significantly. Plasma vasopressin rose significantly after anaesthesia. Plasma aldosterone increased slightly throughout the study, but not significantly during any phase. In conclusion, labetalol with isoflurane-induced hypotension seems to attenuate the stress response in these operations. During hypotension, plasma renin activity is not an essential compensatory mechanism, which antagonises the decrease of blood pressure. Plasma vasopressin has no role in regulating blood pressure during labetalol-induced hypotension.