Abstract
Objective
To determine whether the addition of bupivacaine or contrast medium to methylene blue
dye would affect dye distribution following ultrasound (US)-guided transversus abdominis
plane (TAP) injections.
Study design
Prospective, randomized, blinded cadaveric study.
Animals
A total of 29 fresh Beagle dog cadavers.
Methods
Each hemiabdomen (n = 58) was randomized into one of three groups: group M, 1% methylene blue; group
MB, 50:50 mixture of 1% methylene blue and 0.5% bupivacaine; group MC, 25:75 mixture
of 1% methylene blue and contrast agent (iohexol). TAP injections (0.5 mL kg–1) were performed bilaterally by a trained individual followed by dissection of the
abdominal walls. Craniocaudal and dorsoventral spread along tissue planes was measured.
Staining of branches of the thoracic and lumbar spinal nerves was considered successful
when dye on the nerve was >10 mm. One-way anova with post hoc Tukey test was used to compare craniocaudal and dorsoventral spread and Kruskal–Wallis
test to compare incidence of nerve staining among groups.
Results
TAP injections were successful in 52 out of 58 hemiabdomens. Dorsoventral spread was
greater for group M (60 ± 10 mm) compared with MC (49 ± 9 mm; p = 0.01) but not MB (52 ± 9 mm; p = 0.09). No difference was found in craniocaudal spread or number of nerves stained
among groups.
Conclusion and clinical relevance
The significant difference found in spread of tissue staining between methylene blue
alone and methylene blue mixed with contrast in the TAP blocks should be kept in mind
when interpreting dye-based cadaveric regional anesthesia studies.
Keywords
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Article info
Publication history
Published online: January 30, 2020
Accepted:
January 15,
2020
Received:
August 25,
2019
Identification
Copyright
© 2020 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.
