Bupivacaine muscle injection timing and opioid use in dogs

Abstract

This study investigated the influence of bupivacaine infiltration before or after hemilaminectomy on peri-operative opioid requirement in dogs. Thirty dogs undergoing T3-L3 hemilaminectomy were randomly assigned to receive peri-incisional infiltration of bupivacaine 2 mg/kg into the epaxial muscles before surgery (Group A), at wound closure (Group B), or no infiltration (Group C). Anaesthesia comprised dexmedetomidine 4 mcg/kg and methadone 0.3 mg/kg IV (premedication), alfaxalone IV (induction), and isoflurane in oxygen (maintenance). All dogs received meloxicam SC/PO prior to induction of general anaesthesia. Response to surgery, defined as a change in autonomic physiological variables >20% above baseline, was treated with fentanyl 2.5 mcg/kg boluses, followed by a continuous rate infusion of fentanyl at 5 mcg/kg/h. The Glasgow Composite Pain Score-Short Form (GCPS-SF) was performed before premedication and at regular intervals until 24 h postoperatively. Methadone 0.2 mg/kg analgesia was given IV if GCPS-SF was &#x2265;5/20. Number of intraoperative, postoperative and total analgesic interventions were recorded. Analgesic interventions were analysed using a chi-squared test using a Pocock approach and statistical significance was set at P < 0.029. The number of intra-operative analgesic interventions in Group A (median, 0; range, 0-2), was significantly lower than in Group B (median, 3; range, 0-5) and Group C (median, 3; range, 0-5; P = 0.019). Regarding postoperative interventions, there were significantly fewer in Group A (median, 0; range, 0-1) and Group B (median, 0; range, 0-1) than in Group C (median, 1; range, 0-2; P = 0.047). Group A (median, 0; range, 0-3), had significantly fewer total analgesic interventions than Group B (median, 3; range, 0-6) and Group C (median, 4; range, 1-7; P = 0.014). Bupivacaine reduced peri-operative opioid administration and pre-surgical peri-incisional infiltration yielded the greatest benefit.