Anesthesia and Hypertension

Abstract

Thirty patients (ASA physical status II-III) with a history of arterial hypertension, whose blood pressure (BP) control varied from normotension to moderate hypertension (diastolic BP < 110 mmHg), scheduled for elective surgery under general anesthesia, were randomly assigned to two groups. Group 1 was premedicated 90-120 min prior to induction with diazepam 0.15 mg .cntdot. kg-1 po; group 2, in addition, received clonidine 5 .mu.g .cntdot. kg-1 po. Anesthetic depth was assessed by on-line aperiodic analysis of the electroencephalogram. Following lidocaine 1 mg .cntdot. kg-1 and fentanyl 2 .mu.g .cntdot. kg-1 (group 1 only), anesthesia was induced with thiopental 3-4 mg .cntdot. kg-1 and vecuronium 0.1 mg .cntdot. kg-1 was used to facilitate endotracheal intubation. Anesthesia was maintained with isoflurane in N2O/O2 and supplemented by fentanyl. In group 2, clonidine produced a rapid preoperative control of systolic and diastolic BP from 166 .+-. 32/95 .+-. 14 to 136 .+-. 80 .+-. 11 (P < 0.01), was more effective in blunting the reflex tachycardia associated with laryngoscopy and endotracheal intubation than lidocaine-fentanyl pretreatment. It significantly reduced the intraoperative lability (coefficient of variation) of systolic (P < 0.01) and diastolic BP and heart rate (HR) (P < 0.05), and resulted in significantly slower HR during recovery (P < 0.01). Anesthetic requirements for isoflurane were reduced 40% (P < 0.01) in group 2; narcotic supplementation was also significantly reduced (P < 0.005). The authors conclude that these effects of clonidine are explained by the inhibitory action of clonidine on central monoaminergic systems involved in cardiovascular control, modulation of sleep/wake cycle, cortical arousal, and of nociception.