Motor block following epidural bupivacaine or ropivacaine in dogs: a randomized clinical study

To compare the duration of motor blockade associated with epidural ropivacaine and bupivacaine, each with morphine, in dogs undergoing soft tissue and orthopaedic surgery.

Randomized, parallel, blinded clinical trial.

A group of 29 client-owned dogs, with American Society of Anesthesiologists scores I-III.

After intravenous (IV) acepromazine (10 μg kg^-1) and methadone (0.2 mg kg^-1), anaesthesia was induced (propofol IV) and maintained with isoflurane in oxygen. To provide regional anaesthesia, a lumbosacral epidural injection was administered using either bupivacaine (0.5%, 0.2 mL kg^-1) + morphine (0.1 mg kg^-1) or ropivacaine (0.5%, 0.2 mL kg^-1) + morphine (0.1 mg kg^-1). Postoperative pain was assessed using a composite pain scale and motor block was assessed by observing voluntary movement and the dogs' ability to stand and walk. Assessments were made hourly for 8 hours following epidural drug administration, starting in recovery, and then every 4 hours for 24 hours. Nausea, vomiting, pruritus, voluntary urination and defaecation and administration of rescue analgesia were also recorded. Duration of motor block was compared between groups using parametric and non-parametric (p < 0.05) tests.

Median (interquartile range) time to return of voluntary movement was: 4 hours (3-7) with bupivacaine (n = 15) versus 4 hours (3-6) (n = 14) with ropivacaine, p = 0.21. Return of normal motor function was significantly faster with ropivacaine [10 hours (6-12)] versus bupivacaine [16 hours (8-20)], p = 0.009. No dogs required intraoperative rescue analgesia. Two dogs receiving ropivacaine required postoperative rescue analgesia compared with no dogs receiving bupivacaine, p = 0.22.

In this study epidural ropivacaine + morphine provided an alternative to bupivacaine + morphine based on a faster return of normal motor function and similar requirement for postoperative rescue analgesia.