Intrathecal infusion of bupivacaine with or without morphine for postoperative analgesia after hip and knee arthroplasty

Postoperative pain after major orthopaedic operations can be controlled bycontinuous intrathecal administration of opioids or local anaesthetics.Effective intrathecal analgesia can be achieved through synergism of lowdoses of the two analgesic drugs and, possibly, less drug-related adverseeffects. Therefore, we have evaluated the usefulness of a combined low-dosebupivacaine and morphine infusion in patients undergoing hip and kneearthroplasty. Spinal anaesthesia was induced in 55 ASA I-III patients with0.5% bupivacaine 2 ml via a 28- gauge spinal catheter (L3-4 interspace) and0.5-ml increments were given if needed. Intrathecal 24-h infusionsconsisted of bupivacaine 2 mg h-1 alone (n = 18), bupivacaine 1 mg h-1alone (n = 18) or bupivacaine 1 mg h-1 combined with morphine 8 microgramsh-1 (n = 19). The interview after 3, 6, 12 and 24 h included assessment ofpain at rest and on movement (VAS scale), occurrence of sensory and motorblock and nausea/vomiting. Bupivacaine 1 mg h-1 combined with an infusionof morphine provided as good postoperative analgesia as bupivacaine 2 mg h-1, but motor block disappeared earlier (P = 0.01). Patients in thebupivacaine 1-mg h-1 group required more supplementary doses of oxycodonei.m. than the other groups (P = 0.04). Time to first oxycodone dose fromthe start of intrathecal infusion did not differ between groups. Thefrequency of nausea and vomiting was similar in all groups. In spite ofthis, antiemetic medication was required more often in the bupivacaine 1-mgh-1 group (possible because of opioid rescue medication). On the ward, onepatient in the bupivacaine 2-mg h-1 group experienced a new increase insensory block with concomitant hypotension. One patient in the same grouphad minor decubitus on the heel of the operated leg, probably because ofprolonged motor block. We conclude that intrathecal infusion of acombination of bupivacaine 1 mg h-1 and morphine 8 micrograms h-1 producedadequate postoperative analgesia. Unfortunately, postoperative nausea andvomiting was a frequent disturbing adverse effect.