Postoperative Analgesia with Transdermal Fentanyl or Intramuscular Methadone in Dogs Submitted to Thoracolumbar Hemilaminectomy

Abstract

Background: Postoperative care after thoracolumbar hemilaminectomy in dogs generally includes rest, physical therapy, and analgesics such as opioids. Currently, there is no established standard for the management of postoperative pain in patients undergoing hemilaminectomy. Ideally, an analgesic protocol should provide adequate pain relief with limited sedation, low adverse effects, and postoperative patient comfort. Therefore, this study aimed to evaluate postoperative analgesia using transdermal fentanyl or intramuscular methadone in dogs undergoing thoracolumbar hemilaminectomy associated with intervertebral disc fenestration (HT) for the treatment of intervertebral disc extrusion (IVDE). Materials, Methods & Results: Eight dogs from the Department of Neurology and Neurosurgery of a Veterinary Teaching Hospital, submitted to HT for the treatment of IVDE, were included. The dogs were randomly distributed into 2 groups of equal numbers, namely the transdermal fentanyl (FT) group and the intramuscular methadone (IM) group. At the end of the surgical procedure, a fentanyl adhesive patch was applied to the animals in the FT group, which remained there for 72 h. In the IM group, analgesia was induced by intramuscular administration of methadone at intervals of 6 h until 72 h after surgery. The animals were evaluated using the short form of the Glasgow Composite Measure Pains Scale (CMPS-SF). Evaluations of physiological parameters, side effects, and pain were performed by 2 assessors who had experience using the pain scale and were blinded to the analgesic protocol. Pain evaluations were performed every 2 h (from T4) until 24 h after the surgical procedure. Evaluations were performed every 4 h from 24 h to 48 h after the surgical procedure and at intervals of 24 h from 48 h to 72 h. Discussion: Transdermal fentanyl provided the lowest pain scores, when evaluated by the CMPS-SF, for both assessors. These data are presented as a function of time and shows the variation in pain scores by CMPS-SF over time. It should be noted that, for both assessors, animals in the FT group had lower pain scores than animals in the IM group. There was also less variation in pain scores in the FT group, indicating better analgesic quality. This can be explained by the maintenance of the drug’s plasma concentrations in a stable manner, avoiding periods of greater or lesser pain throughout the evaluation period due to the absence of increases or decreases in plasma concentration. In the IM group, 3 analgesic rescues were required; in the FT group, there was no rescue. Although the data indicate that IM was responsible for a greater occurrence in the number of rescues, it is worth noting that this information is based on a small group of animals. One dog needed 2 rescues (at T4 and T8), regarding which both assessors agreed, while another required one rescue (at T18), but there was a difference of one point between the raters. However, pain scores in all of the cases were considered to be mild, not moderate or severe, with rescues occurring on scores of 5/20. Both fentanyl used by the transdermal route and intramuscular methadone promoted analgesia in the first three postoperative days in dogs undergoing HT. Better stability in postoperative pain scores without the need for analgesic rescue and less occurrence of adverse effects were observed in dogs treated with FT.