The effect of neuraxial morphine on postoperative pain in dogs after extrahepatic portosystemic shunt attenuation

Abstract

ObjectiveTo investigate the analgesic effect of epidural morphine after surgical extrahepatic portosystemic shunt (EHPSS) attenuation. Study designRandomized clinical trial. AnimalsA total of 20 dogs with a congenital EHPSS. MethodsDogs were randomly allocated to be given either a single epidural dose of 0.2 mg kg–1 preservative-free morphine (group M) or not (group C) before surgery. All dogs were administered 0.3 mg kg–1 methadone intravenously (IV) as preanaesthetic medication. Pain scores were determined every 2 hours for the first 24 hours postoperatively using the short-form Glasgow Composite Measure Pain Scale (GCMPS-SF). Dogs with a GCMPS-SF pain score >4/20 or >5/24 received 0.1 mg kg–1 methadone IV as rescue analgesia and were reassessed 30 minutes later. If more than three doses of methadone were administered in a 2 hour period, alternative pain relief was provided and a treatment failure recorded. The GCMPS-SF pain scores and number of rescue analgesia injections were analysed over 24 hours. The last observation carried forward method was applied in case of treatment failure. Food consumption and time to first urination were recorded. Data were analysed using a Mann–Whitney U test and presented as median (minimum–maximum range), with significance set at p < 0.05. ResultsGroup M showed lower GCMPS-SF pain scores [15 (11–41) versus 31 (11–86); p = 0.023] and lower postoperative methadone requirements [0 (0–0.2) versus 0.25 (0–0.5) mg kg–1; p = 0.029] than group C. There were three treatment failures in group C only. Food consumption and time to first urination did not differ between groups. Conclusions and clinical relevanceEpidural morphine reduced the requirement for postoperative analgesia in this study population.