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

Objective: To evaluate the antinociceptive, sedative and cardiopulmonary effects of subarachnoid and epidural administration of xylazine-lidocaine in xylazine-sedated calves.

Study Design: Prospective, crossover study.

Animals: Six clinically healthy Holstein calves.

Materials: 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 (f(R)), mean arterial pressure (MAP), blood pH, arterial partial pressure of oxygen (PaO(2)), partial pressure of carbon dioxide (PaCO(2)), bicarbonate (HCO(3)), base excess (BE), and oxygen saturation (SaO(2)).

Results: 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 PaO(2) decreased significantly, and PaCO(2) increased significantly during anaesthesia. No change was evident in HR, f(R), HCO(3,) BE, or SaO(2).

Conclusion And Clinical Relevance: 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.