Dose requirements, efficacy and side effects of morphine and pethidine delivered by patient-controlled analgesia after gynaecological surgery.

We have compared the dose requirements and side effects of morphine with those of pethidine when administered by patient-controlled analgesia in 40 patients (ASA I-II, 20-65 yr) after elective total abdominal hysterectomy. Patients were allocated randomly, in a double-blind manner, to receive either morphine (bolus dose 2 mg, lockout time 10 min) or pethidine (bolus dose 20 mg, lockout time 10 min) for postoperative pain relief. Mean 24-h morphine and pethidine consumption was 70 (SEM 6.2) mg and 660 (67.8) mg, respectively (ratio 1:9.4). There were no significant differences in postoperative sedation, nausea, pain relief and patient satisfaction (VAS 0-100 mm), and requirements for antiemetics. Four patients receiving pethidine were withdrawn because of postoperative confusion and one receiving morphine because of intractable nausea and vomiting. The 95% confidence interval for this difference between the groups for VAS scores of sedation, nausea and pain were approximately 30 mm.