Xylazine prolongs the duration of action of inverted L blocks in steers.

Objective: To determine if the combination of lidocaine and xylazine has a longer duration of action compared to lidocaine alone when administered as an inverted L block in steers.

Methods: 6 healthy beef-cross steers were enrolled in a randomized crossover study. Both groups received an inverted L block using 6 mg/kg of lidocaine. Group L received lidocaine only, and group LX received lidocaine and 0.02 mg/kg of xylazine. There was a 5-day washout period between treatments. Following administration, the onset and duration of action were assessed through a series of needle pricks along the paralumbar fossa every minute for the first 15 minutes and then every 15 minutes until the return of sensation. Sedation scores and heart rates were also collected. Parametric data were analyzed with a paired t test. Nonparametric data were analyzed with a Wilcoxon signed rank test. A P value < .05 was considered significant. This study was completed in June 2023.

Results: When administered as an inverted L block, the addition of xylazine to lidocaine significantly prolonged the duration of action from 130 ± 43.1 minutes to 197.5 ± 61.7 minutes (P = .027). Sedation scores were higher in the LX treatment group (P = .039). There was no difference between groups for onset of action time (P = 1.0) or heart rate (P = .89).

Conclusions: The combination of lidocaine and xylazine, when administered as an inverted L block, prolongs the duration of blockade.

Clinical relevance: The addition of xylazine to lidocaine for administration as an inverted L block extends the duration of anesthetic effect, confers mild sedative properties, and is readily integrated into clinical practice.