A retrospective study of efficacy and side effects of intrathecal administration of hyperbaric bupivacaine and morphine solution in 39 dogs undergoing hind limb orthopaedic surgery.

Objective  To evaluate the intraoperative efficacy of intrathecal anaesthesia with hyperbaric bupivacaine 0.5% and morphine 1% solution (HIA) in dogs undergoing hind limb orthopaedic surgery, using the cardiovascular response to surgical stimulation and to report the perioperative side effects. Study design  Retrospective clinical study. Animals  Forty-three dogs that underwent general anaesthesia for hind limb orthopaedic surgery between 2010 and 2011. Methods  The anaesthesia records of dogs that received HIA were reviewed. The bupivacaine and morphine doses were calculated based on body mass (BM) and spinal cord length (SCL). Cardiovascular response (CR) to surgical stimulation, the incidence of hypotension, bradycardia, urinary retention, pruritus and offset of motor block were all reported. The intraoperative time-to-event probability of CR was analyzed using Kaplan-Meier survival analysis. Results  The median (range) bupivacaine dose related to BM was 0.57 (0.40-0.78) mg kg(-1) , while that related to SCL was 0.13 (0.08-0.19) mg cm(-1) . A CR was observed in 3/39 (8%) dogs within the first hour after intrathecal injection (Ii) and in 9/39 (23%) dogs over the entire duration of surgery. At 70 minutes from Ii the event-free probability of CR fell below 80%. Hypotension was observed in 12/39 (31%), bradycardia in 6/39 (15%), pruritus in 3/39 (8%), and urinary retention in 3/39 (8%) dogs respectively. Five hours after Ii, 35/39 (89%) dogs were able to walk with only residual ataxia. Conclusions and clinical relevance  Intrathecal anaesthesia with hyperbaric bupivacaine 0.5% and morphine 1% solution provided effective intraoperative antinociception up to 70 minutes in dogs undergoing hind limb surgery. The technique of HIA can provide effective analgesia during short hind limb surgeries in dogs.