Antinociceptive effects of epidural tramadol administration in dogs as an anlagesic for experimental stifle surgery

Tramadol is a centrally acting analgesic with m-opioid and monoaminergic agonist effect. Ten healthy adult dogs were studied (mean ± SEM body weight 17.3 ± 3.8 kg), premedicated with acepromazine (0.05 mg/kg, IM), induced with thiopental (10 mg/kg, IV) and maintained under anesthesia with halothane in oxygen. Twenty minutes after starting halothane anesthesia, tramadol (1.0 mg/kg in 0.22 ml/kg of sterile water) was administered epidurally at the lumbo-sacral space. Surgery began 15 minutes later. Pulse and respiratory rates, systolic, mean and diastolic arterial blood pressure, and pulse oximetry were measured before premedication (baseline), and at fixed intervals after anesthesia induction. Arterial pH, PaO2, PaCO2, HCO3 -, and SaO2 were measured at baseline, immediately before the epidural, and 60, 120, 240 and 360 minutes thereafter. Post-operative analgesia was evaluated for four hours using a scoring system. Statistically significant decrease in arterial blood pressure was observed following anesthetic induction. The PaCO2 increased significantly from baseline at 60 minutes after epidural tramadol. The remaining variables were not significantly different from baseline values. No variables were significantly different from values obtained immediately before tramadol administration. Intraoperative antinociception was considered adequate, with satisfactory post-operative analgesia for four hours. In conclusion, epidural tramadol seems to produce satisfactory antinociception and analgesia without causing clinically significant hemodynamic and respiratory depression in healthy dogs undergoing stifle surgery