Abstract
Objective
To evaluate a regional anesthetic technique for blocking the abdominal midline in
horses.
Study design
Anatomical description and prospective, crossover, placebo-controlled, blinded study.
Animals
Adult horses; two cadavers, six healthy animals.
Methods
In stage 1, 0.5% methylene blue with 0.25% bupivacaine (0.5 mL kg–1) was injected using ultrasonography into the internal rectus abdominis sheath (RAS)
of two cadavers with a one-point or two-point technique. The dye spread was described
after the dissection of the abdomens. In stage 2, each horse was injected with 1 mL
kg–1 of 0.9% NaCl (treatment PT) or 0.2% bupivacaine (treatment BT) using a two-point
technique. The abdominal midline mechanical nociceptive threshold (MNT) was measured
with a 1 mm blunted probe tip and results analyzed with mixed-effect anova. Signs of pelvic limb weakness were recorded.
Results
The cadaver dissections showed staining of the ventral branches from the eleventh
thoracic (T11) to the second lumbar (L2) nerve with the one-point technique and T9–L2
with the two-point technique. Baseline MNTs were, mean ± standard deviation, 12.6
± 1.6 N and 12.4 ± 2.4 N in treatments PT and BT, respectively. MNT increased to 18.9
± 5.8 N (p = 0.010) at 30 minutes, and MNT was between 9.4 ± 2.0 and 15.3 ± 3.4 N from 1 to
8 hours (p > 0.521) in treatment PT. MNTs in treatment BT were 21.1 ± 5.9 to 25.0 ± 0.1 N from
30 minutes to 8 hours (p < 0.001). MNTs after the RAS injections were higher in treatment BT than PT (p = 0.007). No pelvic limb weakness was observed.
Conclusions and clinical relevance
Antinociception of at least 8 hours without pelvic limb weakness was observed in the
abdominal midline in standing horses after the RAS block. Further investigations are
necessary to evaluate suitability for ventral celiotomies.
Keywords
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Article info
Publication history
Published online: March 03, 2023
Accepted:
February 27,
2023
Received:
June 20,
2022
Identification
Copyright
© 2023 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.
