The effect on post-operative pain of intravenous clonidine given before induction of anaesthesia

Treatment of acute post-thoracotomy pain is particularly important not only to keep the patient comfortable but also to minimize pulmonary complications.

This study was designed to test the effect of pre-induction administration of clonidine, given as a single intravenous dose, on post-operative pain scores and fentanyl consumption in patients after thoracic surgery.

Tertiary referral centre. Prospective, randomised, double-blind, placebo-controlled trial.

Sixty patients were randomly allocated to receive clonidine (3 mcg/kg) or saline pre-operatively before induction of anaesthesia. The primary endpoint was pain on coughing (visual analogue scale (VAS) 0-100 mm) 120 min after surgery, time to first analgesic injection in the post-anaesthesia care unit (PACU) and 24-h fentanyl consumption.

For between-group comparisons, t-test and U-test were used as appropriate after checking normality of distribution. The incidence of complications between the groups was compared by Fisher's exact test.

The post-operative VAS for the first 120 min and the fentanyl consumption at 24 h was significantly greater in the placebo group compared with the clonidine group (P<0.05). The sedation score was increased in the clonidine group during study drug infusion, but did not differ significantly on admission to the PACU.

A single intravenous dose of clonidine (3 mcg/kg) given before induction of anaesthesia significantly reduced the post-operative VAS score in the initial period and fentanyl consumption during 24 h after thoracic surgery.