Evaluation of epidural administration of morphine or morphine and bupivacaine for postoperative analgesia after premedication with an opioid analgesic and orthopedic surgery in dogs.

OBJECTIVE: To evaluate the analgesic efficacy of epidural administration of morphine or a morphine-bupivacaine combination administered before orthopedic surgery in dogs that received opioid premedication.

DESIGN: Prospective, randomized, blinded, clinical study.

ANIMALS: 36 healthy adult dogs that underwent elective orthopedic surgery on a pelvic limb.

PROCEDURES: Each dog received 1 of 3 epidural treatments before surgery. Anesthetic and supportive care protocols were standardized. Dogs under going different surgical procedures were randomly allocated among the 3 treatment groups. Respiratory and cardiovascular variables, end-tidal isoflurane concentration, and requirements for rescue analgesia were monitored. Postsurgical analgesia was evaluated with a multiparametric pain scoring system and by determination of rescue analgesia requirements and cortisolemia.

RESULTS: The morphine-bupivacaine combination was associated with lower values than morphine or a saline solution for intraoperative arterial blood pressure; minimum and maximum isoflurane requirements; and postoperative pain scores, rescue analgesia requirements, and plasma cortisol concentrations. Values obtained after administration of morphine alone were not significantly different from those obtained after administration of saline solution for most variables.

CONCLUSIONS AND CLINICAL RELEVANCE: The preoperative epidurally administered morphine-bupivacaine combination induced better analgesia than morphine alone and should be considered for use in clinical patients. The degree of hemodynamic depression associated with the combination was considered acceptable for healthy patients undergoing elective surgery.