Abstract
Studies of pre-emptive analgesia in humans have shown conflicting results. The study design, patient population and the duration of assessment of postoperative pain are important in the evaluation of pre-emptive analgesia. We carried out a prospective, randomized, double-blind controlled study in 80 patients of physical status ASA 1–3 undergoing upper abdominal and thoracic surgery. Patients received two epidural injections, one 20 minutes before induction and the other at the end of surgery. Study solution was either morphine (50 μg/kg), with or without 0.1% bupivacaine in 10 ml of normal saline, or normal saline alone. The study groups (Pre M, Pre MB) were given either morphine or morphine-bupivacaine before induction and saline at the end of surgery. The control groups (Post M, Post MB) were given saline before induction and morphine or morphine-bupivacaine at the end of surgery. Postoperative pain was assessed with a Visual Analogue Scale (VAS) during coughing and deep breathing at six-hourly intervals for five days. Epidural morphine was given if the VAS exceeded 4.
Pre MB compared to Post MB had a significantly increased interval between the analgesic top-ups (P<0.01) and decreased total postoperative morphine requirements (P<0.0001) and number of top-ups (P<0.001). Pre M and Post M were comparable. Pre MB compared to Pre M had significantly decreased total postoperative morphine requirements (P<0.0001) and number of top-ups (P<0.0001). Epidural morphine plus bupivacaine is effective as a pre-emptive analgesic. Morphine plus bupivacaine has better efficacy than morphine given alone before the induction of anaesthesia.