Epidural administration of combinations of ropivacaine, morphine and xylazine in bitches undergoing total unilateral mastectomy: a randomized clinical trial.

OBJECTIVE: To investigate the epidural administration of combinations of ropivacaine, morphine and xylazine in bitches undergoing unilateral mastectomy. STUDY DESIGN: Prospective, randomized, blinded, clinical study. ANIMALS: A total of 22 bitches scheduled to undergo unilateral mastectomy for mammary tumor excision. METHODS: Dogs were anesthetized with acepromazine (0.02 mg kg-1) and morphine (0.3 mg kg-1) intramuscularly, propofol intravenously (IV) and isoflurane. Prior to the beginning of surgery, dogs were randomly administered one of three epidural treatments: ropivacaine (0.75 mg kg-1) with morphine (0.1 mg kg-1) (group RM, n = 7); ropivacaine with xylazine (0.1 mg kg-1) (group RX, n = 8); or ropivacaine with morphine and xylazine (group RMX, n = 7). Cardiopulmonary variables and the expired concentration of isoflurane (Fe'Iso) were recorded intraoperatively. Meloxicam (0.1 mg kg-1) was administered IV during skin closure. Postoperative pain scores were evaluated with the Glasgow composite measure pain scale short form for 24 hours, and rescue analgesia with morphine (0.5 mg kg-1) was administered intramuscularly when pain scores were ≥ 6/24. RESULTS: Fe'Iso was significantly higher in group RM than in groups RX and RMX. Heart rate decreased significantly in groups RX and RMX, but blood pressure remained within acceptable values. The number of dogs administered rescue analgesia within 24 hours was significantly higher in group RX (seven dogs, 87.5%) than in groups RM (one dog, 14.3%; p = 0.01) and RMX (two dogs, 28.6%; p = 0.04). Time to standing was significantly longer in group RX than in group RM. CONCLUSIONS AND CLINICAL RELEVANCE: All epidural treatments provided adequate antinociception with minimal cardiovascular adverse effects during mastectomy. The inclusion of morphine (groups RM and RMX) provided the best postoperative analgesia. Owing to the undesirable effect of xylazine on ambulation, the combination ropivacaine-morphine appeared to provide greater benefits in bitches undergoing unilateral mastectomy.