Intraoperative clonidine modulates sympathetic tone in the early postoperative period after remifentanil. A double blind, placebo-controlled study

Abstract

Abstract Aim of the study : Severe pain following major surgery can impair the control of the cardiovascular system (CVS) by causing sympathetic stimulation, possibly leading to myocardial ischaemia. In this study we examine the influence of intraoperative intravenous (i.v.) clonidine infusion on postoperative analgesia and blood concentrations of noradrenaline and adrenaline after major gynaecological surgery. Methods : All patients underwent an abdominal hysterectomy under balanced general anaesthesia using the new opioid remifentanil. The patients were randomised to receive either 5 μg kg −1 of i.v. clonidine intraoperatively ( n =20), or placebo ( n =20). Over a period of 240 minutes postoperatively we assessed pain intensity, consumption of the opioid piritramide (a μ-receptor agonist) via an i.v. patient controlled analgesia device, together with blood pressure, heart rate, shivering, nausea, vomiting and sedation. Blood concentrations of adrenaline and noradrenaline in both groups were analysed using HPLC. Results : Postoperative pain intensity and opioid consumption were not influenced by intraoperative clonidine. Clonidine, however, did modulate the postoperative sympathetic tone, and the steep rise of plasma catecholamine concentrations, as part of the postoperative stress response, was clearly diminished. The haemodynamic effects of clonidine in the form of a significant reduction in mean arterial pressure and heart rate, were only seen in the first 15 minutes postoperatively. Conclusion : Intraoperative infusion of clonidine 5 μg kg −1 modulates the postoperative sympathetic tone after abdominal hysterectomy under anaesthesia with remifentanil, resulting in a decreased haemodynamic stress response. Surprisingly, a clonidine dose of 5 μg kg −1 had no influence on postoperative pain or opioid consumption.