Aortic surgery: effect of clonidine on intraoperative catecholaminergic and circulatory stability.

Twenty-eight patients presenting for aortic surgery were randomly assigned in a double-blind, placebo-controlled protocol to receive placebo (n = 14) or clonidine (4.7 +/- 1.2 micrograms.kg-1 po; n = 14), in addition to flunitrazepam 120 min before induction of anesthesia. Plasma catecholamines (CA) and hemodynamic variables were determined at 7 stages during surgery. In the placebo group, plasma epinephrine (E) and norepinephrine (NE) had risen twofold at skin closure compared to baseline (E: from 109 +/- 51 pg.ml-1 to 294 +/- 161 pg.ml-1; NE: from 658 +/- 226 to 1150 +/- 494 pg.ml-1). Plasma CA were significantly lower in the clonidine group (P less than 0.001 and 0.01 vs placebo for NE and E respectively). In both groups, similar directional changes were observed for the circulatory variables, upon aortic clamping and declamping. In the clonidine group, however, mean arterial pressure was lower at most stages (P less than 0.05 vs placebo); moreover, stroke volume index was greater in the clonidine group (P less than 0.05) upon declamping. This improved stability in the clonidine group was achieved with a halving in the number of anesthetic/circulatory interventions (P less than 0.05 vs placebo). Provided intravascular volume is adequate, clonidine suppresses the increase in plasma catecholamines induced by aortic surgery and improves circulatory stability, with a reduced number of anesthetic, circulatory adjustments.