A comparison of epidural morphine with low dose bupivacaine versus epidural morphine alone on motor and respiratory function in dogs following splenectomy

Abstract

Objective: To compare post-operative motor function in dogs that received epidural morphine and low dose bupivacaine versus epidural morphine alone following splenectomy.

Study design: Prospective, randomized study.

Animals: 16 client owned dogs undergoing routine splenectomy.

Methods: Following splenectomy dogs were randomly allocated into one of two groups. The morphine group (MOR) was administered epidural morphine (0.1 mg kg(-1)); the morphine-bupivacaine group (MORB) received epidural morphine (0.1 mg kg(-1)) and low dose bupivacaine [0.25 mg kg(-1), (0.167%)]. The adjusted final volume was 0.15 mL kg(-1) in both groups. Motor function and pain assessment were performed at pre-determined times using a simple numerical motor score and the University of Melbourne Pain Scale (UMPS) respectively. An arterial blood gas was performed 2 hours following epidural administration to check for respiratory compromise. If patients scored >7 on the UMPS or were deemed painful by the observer they were administered hydromorphone intravenously and dose and time of rescue analgesia were recorded.

Results: There were no statistically significant differences in motor scores, pain scores, amount of rescue analgesia administered or PaCO2 between treatment groups. No dogs demonstrated respiratory depression or profound motor dysfunction at any time point during the study. 9/16 (56%) dogs did not require rescue analgesia during the first 18 hours following splenectomy.

Conclusions and clinical relevance: The combination of low dose bupivacaine (0.25 mg kg(-1)) and morphine (0.1 mg kg(-1)) when administered epidurally has little effect on post-operative motor function. This combination can be used without concern of motor paralysis in healthy animals.