Postoperative analgesic and cardiopulmonary effects in dogs of oxymorphone administered epidurally and intramuscularly, and medetomidine administered epidurally: a comparative clinical study.

Thirty dogs undergoing pelvic or hindlimb orthopedic surgery were each administered one of the following postoperative treatments: intramuscular oxymorphone 0.15 mg/kg (OIM) (n = 10); epidural oxymorphone 0.05 mg/kg, (OEP) (n = 10); or epidural medetomidine, 0.015 mg/kg (MEP) (n = 10). Heart rate (HR), respiratory rate (RR), and arterial blood pressure were measured before drug injection and 15, 30, 60, 90, 120, 180, 240, 300, 360, 420, and 480 minutes postinjection (PI). Arterial blood gas analysis was performed before and 15, 30, 60, 90, 120, 180, 360, and 480 minutes PI. The duration of analgesia with OEP, 7.62 + 0.30 hours (mean +/- SEM), and MEP, 7.06 + 0.50 hours, was significantly (P < .05) longer than the 4.91 + 0.44 hours obtained with OIM. All treatments resulted in a significant decrease in HR. Four dogs receiving epidural medetomidine each had second degree atrioventricular (AV) block associated with sinus arrhythmia for a brief period during the first 20 minutes after injection. There was no significant difference in arterial blood pressure between OIM and OEP but arterial blood pressure was significantly higher with MEP than with OIM. MEP can provide analgesia comparable with OEP, but bradycardia and second degree AV block will develop in some cases.