Background and Objectives Adequate postoperative pain relief has been achieved in orthopedic patients by subarachnoid bolus administration of plain bupivacaine. This prospective randomized study compares bolus injections of bupivacaine with a patient controlled infusion via subarachnoid 28-gauge microcatheters for postoperative analgesia after elective hip replacement.

Methods Forty-two patients (mean age, 69 ± 11 years) were randomly allocated to one of two groups. Group 1 patients received a constant subarachnoid infusion of 0.6 mg/h of bupivacaine by a patientcontrolled device and were allowed to self-administer 0.6 mg every 30 minutes Group 2 patients received a nurse-administered bolus of 3.75 mg of plain bupivacaine on request. Pain was assessed by patients and nurses by a visual analog scale (VAS) every hour. The degree of motor block and the level of analgesia were documented every 4 hours. Hemodynamic and respiratory parameters were recorded hourly. Differences between groups were tested by analysis of variance for repeated measurement.

Results Technical problems occurred in six patients were more frequent in group 1 but none in group 2. Patient-controlled analgesia resulted in lower pain scores than bolus application during 18 postoperative hours (VAS score 19 ± 19 mm in group 1 and 39 ± 30 mm in group 2; P < .01). Lower total doses of bupivacaine were required in group 1 (17.6 ± 4 mg) than in group 2 (22.3 ± 7 mg: P < .05). The groups did not differ with respect to the degree of motor block (Bromage score 3.5 ± 0.5), the sensory level (L1-2 ± 1), or hemodynamic or respiratory parameters.

Conclusion In spite of a higher incidence of technical problems, patient-controlled analgesia with a continuous background infusion via microspinal catheters provides more effective postoperative analgesia, without hemodynamic or respiratory side effects, than bolus administration.