Evaluation of the usefulness of intrathecal bupivacaine infusion for analgesia after hip and knee arthroplasty.

Spinal anaesthesia in 47 ASA I-III patients was induced with 0.5% bupivacaine 2 ml via a 28-gauge spinal catheter (L3-4 interspace) and 0.5-ml increments were given if needed before or during hip or knee arthroplasty. Intrathecal 24-h infusions consisted of 0.5% bupivacaine 0.4 ml h-1 (2 mg h-1) (n = 12), 0.5% bupivacaine 0.2 ml h-1 (1 mg h-1) (n = 12) or saline (n = 11) (12 exclusions). Patients received oxycodone 0.1-0.14 mg kg-1 i.m. for rescue analgesia. Infusion of bupivacaine 2 mg h-1 provided significantly better postoperative analgesia (19 oxycodone doses per group in 24 h) compared with bupivacaine 1 mg h-1 (36 doses of oxycodone per group) and saline (52 doses per group) (P < 0.05). Five patients in the bupivacaine 2-mg h-1 group and none in the other groups had measurable sensory block 24 h after the infusion was started. Three patients in the bupivacaine 2-mg h-1 group, two with concomitant arterial hypotension, and one patient in the bupivacaine 1-mg h-1 group experienced an increase in block on the ward. The incidence of nausea and vomiting was similar in all groups. Although an effective analgesic, intrathecal infusion of bupivacaine 2 mg h-1 cannot be recommended for routine pain relief because of the risk of increasing spinal block. Technical problems (19%) also reduced the overall efficacy of the continuous intrathecal analgesic regimen.