Intraoperative Ketamine Infusion and Postoperative Pain Trajectories, Rescue Analgesia, and Persistent Postsurgical Pain in Dogs Undergoing Orthopedic Surgery: A Retrospective Cohort Study

Ketamine is included in multimodal analgesic protocols, but evidence for its benefit on postoperative and persistent pain in dogs is limited. This retrospective cohort study evaluated the association between perianesthetic ketamine infusion and postoperative pain trajectories, rescue analgesia, and signs of persistent postsurgical pain in 508 client-owned dogs undergoing orthopedic surgery (May 2023–June 2024). Signalment, procedure, anesthetic management, pain scores, and rescue opioids during the first 48 postoperative hours were recorded, with findings at recheck ≥ 2 months. Group-based trajectory modeling identified pain trajectories; associations were assessed using multivariable regression, adjusted for confounders. Ketamine was administered to 101 dogs (19.9%) at a median (Q1, Q3) rate of 0.50 (0.33, 0.96) mg/kg/h. Two trajectories were identified: no pain (83.7%) and mild-to-low pain (16.3%). Ketamine infusion was not associated with trajectory membership (adjusted p = 0.22), rescue analgesia (p = 0.44), or opioid requirement (p = 0.07). At recheck, 37.8% of the 251 dogs with follow-up showed persistent pain and/or incomplete limb function, with no association with perianesthetic ketamine infusion (p = 0.15). In dogs undergoing orthopedic surgery and receiving multimodal analgesia, perianesthetic ketamine, at the doses and infusion durations used, was not associated with improved short-term or persistent pain outcomes.