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Objective To assess the advantages of patient-controlled analgesia (PCA) in patients undergoing extracorporeal shockwave lithotripsy (ESWL) for urinary stones. Patients and methods Between December 1995 and May 1996, a prospective study was carried out on 100 patients who underwent ESWL for urinary stones. The patients were assigned to two equal groups, one receiving PCA and the other pethidine (control). Patients in the PCA group self-administered varying doses of intravenous alfentanil according to their pain tolerance, while those in the control group were given a single bolus dose of 1 mg/kg body weight intravenous pethidine by the attending urologist before the start of the procedure. The stone site, maximum energy level achieved, number of shock waves given, duration of procedure, pain scores, patient tolerance and acceptance were recorded to assess the efficacy of PCA compared with analgesia controlled by the physician. Results Both groups were matched for age, body weight, stone location and number of shocks given. The PCA group received a mean of 1.03 mg alfentanil while the control group received a mean of 62.5 mg pethidine. The maximum discharge voltage of 16 kV was achieved in all but one patient (98%) in the PCA group whereas only 21 patients (42%) in the control group attained this level. The mean treatment duration was less in the PCA group (32.8 min) than in the control group (44.5 min), the mean pain score lower (3.76 and 4.62, respectively) and the incidence of nausea and vomiting much less (22% and 60%, respectively). In addition, all 21 patients in the PCA group who had received intravenous pethidine during previous sessions of ESWL chose PCA as the better form of analgesia. There were no adverse effects in the PCA group except for one patient whose arterial oxygen saturation decreased transiently. Conclusion PCA enables the urologist to achieve better patient compliance through better pain control; its application has maximized the use of lithotripsy and the patients' acceptability for this form of analgesia is confirmed. We recommend that this form of analgesia be used for ESWL. [ABSTRACT FROM AUTHOR]