Opioid requirements after locoregional anaesthesia in dogs undergoing tibial plateau levelling osteotomy: a pilot study

Abstract (word count 299) Objective To determine the intraoperative and early postoperative opioid requirement after sciatic and/or femoral nerve block or epidural anaesthesia in dogs undergoing tibial plateau levelling osteotomy (TPLO). Study design Prospective, masked, pilot, randomised, clinical trial. Animals A total of 40 client owned dogs undergoing TPLO. Methods Each dog was randomly assigned to group SF (combined sciatic and femoral nerve block), group S (sciatic nerve block), group F (femoral nerve block) or group E (epidural anaesthesia). A total of 0.3 mL kg-1 of ropivacaine 0.5% was administered to each nerve or in the epidural space. Intraoperatively, fentanyl (2 μg kg-1) was administered intravenously when heart rate, mean arterial pressure or respiratory rate increased by >30% compared to baseline values. Postoperatively, a visual analogue scale (VAS) and a modified German version of the French pain scale (4AVet) were used to assess pain every 30 minutes for 150 minutes and again once the morning after surgery. Methadone (0.1 mg kg-1) was administered intravenously if the VAS was ≥ 4 cm (maximal value 10 cm; median [interquartile range]) or the composite pain score was ≥ 5 (maximal value 15; median [interquartile range]). Significance was defined as p ≤ 0.05. Results Groups SF and E required less total intraoperative and early postoperative opioid doses compared to groups S and F (p = 0.031). No dogs in groups SF had a block failure or required postoperative methadone. A reduced methadone requirement was found for SF compared to all the other groups up to 150 minutes after recovery (p = 0.041). Conclusion and clinical relevance Combined sciatic and femoral nerve block and epidural anaesthesia lead to less cumulative consumption of perioperative opioids than single nerve blockade. Sciatic or femoral nerve block alone might be insufficient to control nociception and early postoperative pain in dogs undergoing TPLO.