Distal paravertebral block anesthesia with a mixture of lidocaine and xylazine has a longer duration than a lidocaine block coupled with intramuscular xylazine in steers.

Objective: To determine whether the site of administration of xylazine alters its impact on lidocaine's duration of action when administered as a distal paravertebral block (DPV) in steers.

Methods: 6 healthy steers were used. Unilateral DPVs were performed at L1, L2, and L4. Each steer received 2 treatments in a blinded random crossover study. The local xylazine treatment group received 6 mg of lidocaine/kg mixed with 0.02 mg of xylazine/kg as a DPV, followed by an injection of 0.9% NaCl in the cervical musculature. The systemic xylazine treatment group received 6 mg of lidocaine/kg as a DPV and 0.02 mg of xylazine/kg in the cervical musculature. Sensation was assessed by response to needle pricks along the paralumbar fossa with a 22-gauge hypodermic needle. The time of onset, duration of action, sedation score, and heart rate were compared between treatments. Data are reported as mean ± SD. This study was completed over a 2-week period in May 2023.

Results: The duration of anesthesia was significantly prolonged after DPV in steers treated with local xylazine (186.7 ± 58.7 minutes) compared to systemic xylazine (95 ± 36.3 minutes). Both treatments were associated with mild decreases in heart rate and sedation but were not significantly different between groups.

Conclusions: The addition of xylazine to lidocaine when administered as a DPV provides a longer duration of anesthesia than when xylazine is administered at a distant site to local anesthetic solution deposition.

Clinical relevance: The combination of lidocaine and xylazine when administered as a DPV prolongs the duration of action of lidocaine and is a practical, inexpensive technique.