Antinociceptive, sedative and cardiopulmonary effects of subarachnoid and epidural xylazine-lidocaine in xylazine-sedated calves

To evaluate the antinociceptive, sedative and cardiopulmonary effects of subarachnoid and epidural administration of xylazine-lidocaine in xylazine-sedated calves. Prospective, crossover study. Six clinically healthy Holstein calves. The calves were allocated randomly to receive two treatments, subarachnoid or epidural xylazine (0.025 mg kg⁻¹)-lidocaine (0.1 mg kg⁻¹) diluted to a total volume of 5 mL with physiological saline. Prior to either epidural or subarachnoid injection, sedation was induced in all calves by intravenous administration of 0.1 mg kg⁻¹ xylazine. The quality and duration of antinociception and sedation were monitored. Areas of the cranial abdomen, umbilicus, and caudal abdomen were evaluated for antinociception using pinprick tests with a scoring system of 0-3 (0, none; 1, mild; 2, moderate; 3, complete). Sedation was assessed by using a 4-point scale (0, none; 1, mild; 2, moderate; 3, deep). The following cardiopulmonary variables were monitored: heart rate (HR), respiratory rate (fR), mean arterial pressure (MAP), blood pH, arterial partial pressure of oxygen (PaO₂), partial pressure of carbon dioxide (PaCO₂), bicarbonate (HCO₃), base excess (BE), and oxygen saturation (SaO₂). Xylazine sedation and subarachnoid xylazine-lidocaine resulted in significantly higher nociceptive block than the epidural technique. Moreover, subarachnoid xylazine-lidocaine induced a significantly longer duration of complete antinociception (median [IQR]) in the cranial abdomen (15.0 [15.0-30.0] versus 7.5 [1.3-10.0] minutes; p < 0.05) and umbilicus (45.0 [32.5-57.5] versus 10.0 [6.3-17.5] minutes; p < 0.05) compared with epidural xylazine-lidocaine. There was moderate sedation with both techniques. In both treatments, blood pH, MAP and PaO₂ decreased significantly, and PaCO₂ increased significantly during anaesthesia. No change was evident in HR, fR, HCO₃, BE, or SaO₂. The subarachnoid injection provided better quality and longer duration of antinociception than epidural administration of the same doses of xylazine-lidocaine in xylazine-sedated calves, while cardiopulmonary depressant effects were observed with both regimens.