Evaluation of epidural morphine and incisional bupivacaine for analgesia following hemilaminectomy in the dog

A blind, placebo–controlled clinical trial was performed to evaluate the postoperative analgesic effect of topically administered, intraoperative, epidural morphine (Duramorph™) and intramuscular infiltration of the incision site with bupivacaine prior to closure of the skin in dogs undergoing hemilaminectomy for Hansen type I Intervertebral Disk Disease (IVDD). Thirty-three dogs were randomly allocated into four treatment groups: epidural Duramorph™ with incisional bupivacaine (DUR/BUP), epidural saline with incisional bupivacaine (SAL/BUP), epidural Duramorph™ with incisional saline (DUR/SAL), and epidural saline with incisional saline (SAL/SAL). All dogs were premedicated with a standard protocol and were anesthetized with propofol and isoflurane. After surgery, scores were assigned using a visual analog scale (VAS) for both pain and sedation and a composite pain scale (CPS). In addition, a von Frey anesthesiometer was used to determine pain thresholds at 1 cm and 3 cm from the surgical incision line (primary hyperalgesia) as well as on the lateral aspect of the stifle (secondary hyperalgesia). Assessments were carried out at fixed intervals over the 48 hour postoperative period. Significant differences were found between those groups treated with the epidural Duramorph™ and those that received epidural saline. Those dogs in the DUR/BUP and DUR/SAL groups exhibited lower von Frey pain thresholds and higher VAS and CPS scores than the SAL/BUP and SAL/SAL groups. The administration of bupivacaine had no significant effect on any measured outcome. The authors conclude that topically administered epidural Duramorph™ and intramuscular incisional bupivacaine do not enhance analgesia following hemilaminectomy in the dog.