EFFECTS OF ORAL CLONIDINE PREMEDICATION AND POSTOPERATIVE IV INFUSION ON HEMODYNAMIC AND ADRENERGIC RESPONSES DURING RECOVERY FROM ANESTHESIA

The effects of clonidine, a central alpha2-adrenoreceptor agonist, on haemodynamic and catecholamine changes were assessed during emergence from anaethesia, a period which is associated with increased sympathetic nervous discharge, hypertension and tachycardia. According to a double-blind randomized design, 32 patients received either clonidine, preoperatively given by oral route (3.5-mu-g . kg-1) and postoperatively by i.v. infusion (0.3-mu-g.kg-1.h-1), or a placebo. Perioperative management was similar in both groups. Measurements were made in the recovery room, before starting clonidine or placebo infusions for evaluation of clonidine premedication, and then during infusion as follows: when core temperature reached 37-degrees-C; then 2 h, and 6 h later. Prior to starting infusions, mean blood pressure (88 +/- 15 vs 103 +/- 14 mmHg) (11.7 +/- 2.0 vs 13.7 +/- 1.9 kPa), heart rate (67 +/- 8 vs 87 +/- 17 beats.min-1) and plasma norepinephrine levels (462 +/- 393 vs 615 +/- 361 pg.ml-1) were lower in the clonidine group. Only at latest measurement (6 h after core temperature reached 37-degrees-C) did clonidine elicit significant effects. The values during clonidine infusion compared to placebo were at this time: mean blood pressure (73 +/- 10 vs 86 +/- 13 mmHg) (9.7 +/- 1.3 vs 11.5 +/- 1.7 kPa), heart rate (71 +/- 6 vs 93 +/- 13 beats.min-1) and plasma norepinephrine levels (240 +/- 224 vs 451 +/- 111 pg.ml-1). Our results suggest that: 1) properative clonidine may improve the haemodynamic profile associated with anaesthetic discontinuation, but 2) i.v. infusion (0.3-mu-g.kg-1.h-1) did not prolong this effect during the early postoperative period in the face of the sympathetic nervous discharge of recovery.