The objective of this randomized controlled prospective study was to compare the effects of caudal epidural xylazine versus saline on tolerance of paravertebral nerve block and flank surgery and on post-operative pain in heifers used for a veterinary student training laboratory.
Fourteen one-year-old, nongravid, healthy Holstein heifers, weighing 360 ± 5 kg, were included.
Xylazine (0.05 mg kg1) or 0.9% saline (5 mL) was injected using a caudal epidural technique to seven heifers undergoing a flank surgery. Nerve block of the right paravertebral fossa was performed using equal parts of lidocaine 2% and bupivacaine 0.5%.
Heart and respiratory rates, rectal temperature, rumination frequency, and appetite were recorded before and at 4, 8, and 24 hours after surgery. Scores were recorded for: tolerance of local anesthesia injections (pre-operatively), sedation, ataxia and distress (intraoperatively, every 30 minutes), and pain (4, 8, and 24 hours post-operatively).
Results: The animals reaction to local anesthetic injection was judged to be less in the xylazine group by both an experienced observer (p < 0.001) and student surgeons (p < 0.01).
The xylazine group required less local anesthetic (82.9 ± 13.8 mL) versus the saline group (108.4 ± 19.6 mL, p = 0.035).
Intraoperatively, xylazine heifers were more sedated at all times (p-values from <0.001 to 0.017), were more ataxic for the first 1.5 hours (p-values from <0.001 to 0.026), and lower in distress at all times (p-values from <0.001 to 0.007).
No difference in post-operative pain or physiologic variables was found, except immediately post-operatively, rectal temperature was higher in the xylazine group (39.5 ± 0.3 °C) than in the saline group (38.6 ± 0.2 °C, p < 0.001).
Compared with epidural saline, caudal epidural xylazine reduced distress of anesthetic injection and surgical manipulation in heifers and an improvement in animal well-being was apparent.
This effect may have been as a result of sedation. Pre-operative epidural xylazine did not appear to improve post-surgical analgesia in our study.
Source: Chevalier, Helene M, Provost, Patricia J & Karas, Alicia Z (2004): Effect of caudal epidural xylazine on intraoperative distress and post-operative pain in Holstein heifers. In: Veterinary Anaesthesia and Analgesia 31 (1), 1-10.
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