Objective: To describe the prevalence of dysphoria after intraoperative administration of fentanyl by infusion and identify other risk factors influencing this in dogs undergoing stifle surgery.

Study design: Prospective, randomized clinical study.

Animals: Dogs (n = 92) that had tibial plateau leveling osteotomy (TPLO) or tibial tuberosity advancement (TTA).

Methods: Dogs were anesthetized using a standardized anesthetic protocol, and randomly assigned to receive a loading dose followed by 1 of 3 infusions of fentanyl perioperatively: 2 μg/kg/h, 10 μg/kg/h, or 20 μg/kg/h. Dog characteristics and all additional medications were recorded and included as part of the statistical analysis. Dog behavior was scored before anesthesia and during recovery using a scale of 1-4 (Appendices A and B). If no improvement in behavior was seen in 3-5 minutes postextubation, dogs with a score of 3 or 4 during recovery were administered fentanyl (2 μg/kg intravenously [IV]) in the event that the behaviors associated with the higher scores were related to pain. If they did not respond favorably to the administration of additional fentanyl and wound palpation did not elicit a response, but the untoward behaviors continued, dogs were administered either a tranquilizer, sedative, or opioid antagonist, and were considered dysphoric.

Results: Of 92 dogs, 22 (23.9%) were considered dysphoric using aforementioned criteria.

Conclusions: About one-fourth of dogs enrolled in this study were dysphoric based on study criteria.