PURPOSE: The purpose of this study was to evaluate the effect of perioperative oral clonidine on postoperative analgesia and PCA morphine requirements in adult patients after major orthopaedic knee surgery. METHODS: In this prospective, double blind, placebo-controlled study 44 patients undergoing either total knee replacement or hemiarthroplasty of the knee were randomly assigned to receive oral placebo or clonidine (5 micrograms . kg-1) 1.5 hr before surgery, and at 12 hr, and 24 hr after the initial dose. Five patients were subsequently withdrawn from study. No other preoperative drugs were given. Preoperative sedation score was recorded. A standardized general anaesthetic was administered to all patients. Postoperative blood pressure, heart rate, PCA morphine use, visual analogue score (VAS) for pain, sedation, nausea, and pruritus were recorded for 36 hr postoperatively. RESULTS: The cumulative PCA morphine used was 37% lower after clonidine 57.3 +/- 26.8 mg (mean +/- SD) compared with placebo 91 +/- 31.6 mg (P = 0.031). There was no difference in pain or sedation scores postoperatively but patients who received clonidine were more sedated preoperatively (P < 0.001) and had a lower mean arterial blood pressure throughout the period of study by 10 to 26 mmHg (P < 0.0001). Clonidine reduced the incidence of postoperative nausea (25% vs 74%) (P < 0.01) and vomiting compared with placebo (10% vs 53%) (P < 0.01) and required less antiemetic (dimenhydrinate 37.5 +/- 20.9 mg vs 82.1 +/- 49.4 mg) but not statistically significant (P = 0.065). CONCLUSIONS: Oral clonidine is a useful component to postoperative balanced analgesia as it decreases PCA morphine requirements and decreases the incidence of nausea and vomiting.
