The effect of topical epidural morphine and dexmedetomedine for post-operative analgesia after hemilaminectomy in dogs： A prospective randomized study

Hansen type I intervertebral disc herniation occurs commonly in chondrodystrophied dogs, and the surgical management is to perform hemilaminectomy to remove the herniated disc material. Multimodal analgesia is usually applied to patients receiving hemilaminectomy. The higher dose of opioids, the stronger analgesia it provides, but the undesirable side effects usually occur subsequently. Recently, topical epidural analgesia had been applied in human and veterinary medicine, which showed effective analgesia with longer duration, compared to the traditional epidural analgesia.
The aim of the study is to evaluate the post-operative analgesic effect of topical epidural morphine and dexmedetomidine in dogs underwent hemilaminectomy for thoracolumbar intervertebral disc disease.
Dogs underwent hemilaminectomy were included in the study. In most dogs, disc fenestration was also performed. During the surgery, single dose of meloxicam intravenously and fentanyl constant rate infusion (CRI) were administered. At the end of surgery, a hemostatic sponge contained morphine and dexmedetomidine (study group) or saline (control group) was placed on the spinal cord via the hemilaminectomy bone defect. Fentanyl CRI was stopped when extubated. Post-operative pain was evaluated at specific time point after extubation (every 2 hours for the 16 hours, every 4 hours for the following 8 hours, then every 8 hours for the next 24 hours), by using “University of Melbourne Pain Scale” and “Short-form Glasgow Composite Measure Pain Scale”. Fentanyl intravenous bolus followed by CRI was administered when the pain score reached the rescue standard.
There were 13 dogs enrolled in the study, 7 in the study group and 6 in the control group. The mean rescue time of the study group was 8.29± (2.93) hour, and 8± (3.35) hour in the control group. The mean total scores of UMPS and GCPS –SF were 51.71± (9.23), 38.14± (4.98) and 52± (9.17), 34.83± (11.32) in the study and control group, respectively. Topical epidural morphine and dexmedetomidine sponge can provide about 8-hour analgesia in the study group, but the analgesic duration and effect seemed similar to the control group. No significant difference was detected between study and control group regarding the time of rescue analgesia, total pain scores, pain scores per time point, and total consumption of fentanyl. However, many biases potentially exist in this study, including small sample size, sensitivity of the pain evaluation, the strong analgesic effect of meloxicam and pain assessment influenced by the side effects of fentanyl CRI.
Base on the results in this study, it remained unclear whether there is an advantage to the use of the morphine and dexmedetomidine sponge in dogs receiving hemilaminectomy. Study with large scale and modified design is needed to
elucidate the effect of topical epidural analgesia.