Analgesic effects of trigeminal/facial nerves blockade by ropivacaine or bupivacaine in dogs undergoing total ear canal ablation/lateral bulla osteotomy : comparison with those obtained by morphine systemic use

Aim of this study was to evaluate postoperative analgesic effects of the preoperative blockade (through nerve locator) with bupivacaine (BVC) or ropivacaine (RVC) on the trigeminal (mandibular branch) and facial (auricular palpebral branch) nerves, in comparison with those obtained by systemic use of morphine (MOR), in dogs undergoing total ear canal ablation and lateral bulla osteotomy (TECA-LBO). 18 dogs were randomly allocated into 3 groups: preoperative BVC (1 mg kg-1) block, preoperative RVC (1 mg kg-1) block, and preoperative systemic MOR (0.2 mg kg-1 IM). Anaesthetic protocols included preoperative atropine (0.03 mg kg-1 IM) and acepromazine (0.03 mg kg-1 IM), propofol for induction (4 mg kg-1 IV) and isoflurane with oxygen (100%) for maintenance. All dogs were intraoperatively monitored for main cardiovascular and respiratory parameters, including end-tidal isoflurane concentration (Et-ISF%). After surgery, analgesic effects were evaluated for 24 hours by the same observer through pain scores using the Ohio State University numerical scale. Rescue analgesic drugs were administered when score was 3 points over in one parameter. Intraoperative recorded data were analyzed by ANOVA, and postoperative pain scores by Tukey post-hoc test (P <0.05). Intraoperative parameters did not show significant differences among groups, with the exception for the levels of Et-ISF% significatively lower in group 1 (mean = 1,34 ±0,22) and in group 2 (1,45 ±0,24) respect to those in group 3 (1,59 ±0,27). Postoperative pain scores resulted to be significantly lower in groups treated by anaestehtic blocks compared with those obtained by MOR systemic use, particularly for wound palpation and sedation parameters. All patients in the MOR group required rescue analgesics after 4 hours, while those of the other groups did not.. The preoperative trigeminal and facial nerves blocks with BVC or RVC seem to be more effective for pain control than MOR systemic use in dogs undergoing TECA-LBO. Blocks by local anaesthetics, additive to general anaesthesia, have shown to improve analgesic response to surgical pain. No complication or toxic effects were recorderd during blockade