Effects of clonidine on variation of arterial blood pressure and heart rate during carotid artery surgery

Abstract

The effect of oral premedication with 300 micrograms of clonidine on systemic arterial pressure, heart rate, and plasma norepinephrine levels was assessed in a double-blinded, placebo-controlled study conducted in 29 patients subjected to carotid artery surgery (CAS). Anesthesia was induced with thiopental, 6 mg/kg, and alfentanil, 0.05 mg/kg, and maintained with alfentanil and 0.6% isoflurane in 50% N20/O2. The study was divided into five periods as follows: (1) anesthesia to start of surgery; (2) surgery to carotid artery clamping; (3) carotid artery clamping to unclamping; (4) carotid artery unclamping to the end of surgery; and (5) the first 4 postoperative hours in the recovery room. In the clonidine group (n = 14), plasma norepinephrine concentrations were significantly lower before induction of anesthesia and during the operative period. Heart rate and systemic arterial pressure were lower (P less than 0.01) in the clonidine group at 3 different time intervals (control, carotid clamping, carotid unclamping). However, during each of the previously defined periods, the variability of heart rate and systemic arterial pressure, assessed by the coefficient of variation, was not different between the two groups. The lability of these hemodynamic parameters, expressed as the percentage of values, which increased or decreased more than 20% of control values during the corresponding period, was also comparable between the two groups. The number of patients who experienced at least one episode of hypertension (systolic arterial pressure greater than 180 mm Hg), hypotension (systolic arterial pressure less than 100 mm Hg), or bradycardia less than 45 beats/min was not different between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)