Recovery quality and antinociceptive effects following rectus abdominis sheath block in dorsally recumbent horses: an experimental study.

OBJECTIVE

To evaluate recovery quality and antinociception following rectus abdominis sheath (RAS) block performed with bupivacaine in dorsally recumbent anesthetized horses.

STUDY

DESIGN

Randomized, crossover experimental study.

ANIMALS: Six healthy adult horses.

METHODS

Each horse was anesthetized twice using a standardized isoflurane protocol and underwent bilateral two-point RAS injections (total of 1 mL kg-1) of either 0.2% bupivacaine treatment (BT) or 0.9% NaCl treatment (ST) under ultrasound guidance. Horses remained anesthetized for 1 hour after the block. During anesthesia recovery, accelerometry-derived recovery scores (RS), times to first movement, sternal recumbency, the number of standing attempts, and time to stand were recorded. Mechanical nociceptive threshold (MNT), heart rate (HR), respiratory rate (fR), and ataxia score (AS, 0 = no ataxia to 4 = severe ataxia) were measured at baseline and from 2 to 10 hours after anesthesia recovery. Comparisons were conducted using paired t-tests, Wilcoxon tests, and generalized linear mixed models (α = 0.05).

RESULTS

The RS, number of standing attempts, and recovery times did not differ between BT and ST (p > 0.366). The baseline MNT was 15.3 (12.6-16.8) N and 14.5 (7.8-16.3) N for BT and ST, respectively. The MNT (95% confidence interval) after RAS block was 22.2 (16.2-25.0) N and 13.7 (10.0-18.8) N for BT and ST, respectively (p < 0.001). Baseline HR and fR were 34 (28-44) and 30 (28-36) beats minute-1, and 20 (16-20) and 16 (12-20) breaths minute-1 for BT and ST. The baseline AS for BT and ST was 0. No clinical effects on HR, fR, or AS after RAS block were observed in BT and ST.

CONCLUSIONS

A RAS block in anesthetized horses was associated with postanesthetic antinociception. No differences in recovery-related variables or adverse events were detected between treatments.

CLINICAL RELEVANCE: The RAS block may provide postanesthetic antinociception in horses without affecting recovery or increasing adverse events.