Comparison of intratesticular lidocaine, sacrococcygeal epidural lidocaine and intravenous methadone in cats undergoing castration: a prospective, randomized, investigator-blind clinical trial.

Objective: The objective of this study was to compare three analgesic protocols for feline castration.
Study Design: Prospective, randomized clinical study.
Animals: Forty-nine client-owned cats.
Methods: Cats were injected with intramuscular (IM) dexmedetomidine (15 μg kg ^-1 ) and alfaxalone (3 mg kg ^-1 ) and assigned randomly to one of three treatment groups. Group ITL (n = 15) were administered intratesticular 2% lidocaine (0.05 mL each testicle), group SCL (n = 15) a sacrococcygeal epidural injection of 2% lidocaine (0.1 mL kg ^-1 ) and group IVM (n = 19) intravenous (IV) methadone (0.3 mg kg ^-1 ), before surgery. Cardiorespiratory variables were recorded. In case of autonomic nociceptive response, IV fentanyl (2 μg kg ^-1 ) was administered. During recovery, time from IM atipamezole (75 μg kg ^-1 , administered at the end of surgery) to sternal recumbency and to active interaction was recorded. Quality of recovery was assessed using a simple descriptive scale. Postoperative analgesia was evaluated using a visual analogue scale and the UNESP-Botucatu multidimensional composite pain scale (MCPS) at return of active interaction and then 1, 2 and 3 hours later.
Results: The three analgesic protocols were comparable in terms of intraoperative fentanyl and propofol requirement. Cardiorespiratory variables stayed within normal ranges in the majority of the cases, although group IVM had the lowest intraoperative respiratory rate (p = 0.0009). No differences were detected between groups in UNESP-Botucatu MCPS scores (p = 0.21). However, group ITL showed higher visual analogue scale score than group IVM (p = 0.001). Four cats enrolled in group ITL, as well as three of group SCL and one of group IVM, required rescue analgesics before the completion of pain assessment.
Conclusions and Clinical Relevance: Intratesticular and sacrococcygeal epidural lidocaine injections could be regarded as good alternatives to systemic opioids in cats undergoing castration, although the benefits of these techniques seem to be of shorter duration than IV methadone.
(Copyright © 2017 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. All rights reserved.)