RESUMEN
<p><b>OBJECTIVE</b>To compare the analgesic effect and side effects of morphine for intravenous patient-controlled analgesia (PCA) with or without low-dose naloxone after abdominal surgery.</p><p><b>METHODS</b>Fifty-nine ASA I - II patients undergoing elective abdominal surgery were randomly divided into two groups: group morphine received postoperative PCA with 0.4 mg/ml morphine (a 1 mg bolus with a 5 min lockout), group naloxone received morphine 0.4 mg/ml with 6 microg/kg naloxone. Blood pressure, heart rate, respiratory rate, and pulse oxygen saturation were monitored. Visual analogue scale (VAS), nausea/vomiting, pruritus, sedation and consumption of morphine were recorded for 24 hours.</p><p><b>RESULTS</b>VAS had no difference between group morphine and group naloxone, but group naloxone had significantly lower VAS for pain at rest or movement (beyond 4-8 h), and the incidence of nausea/vomiting significantly decreased in group naloxone (P < 0.05). No differences existed in pruritus, sedation, respiratory rate, and hemodynamic parameters between these two groups. The 24 hours postoperative morphine consumption was (36.6 +/- 13.5) mg in group naloxone and (43.7 +/- 14.6) mg in group morphine (P < 0.05).</p><p><b>CONCLUSION</b>For morphine PCA, morphine with 6 microg/kg naloxone is effective in preventing some PCA morphinerelated side effects. Naloxone not only reduces postoperative morphine requirements but also improves the analgesic effect.</p>