Open approach to the ventral transversus abdominis plane in the dog: evaluation and injectate dispersion in cadavers

A surgical approach to the transversus abdominis plane in cats: A cadaver study

OBJECTIVE

To evaluate an intra-abdominal approach to the transversus abdominis plane (TAP) in cats.

STUDY DESIGN

Prospective descriptive cadaveric study.

ANIMALS

Nine adult feline cadavers.

METHODS

A 5 cm ventral midline incision, centered on the umbilicus was created. The TAP was accessed at the midpoint of the incision using a 22 gauge, 31.8 mm catheter. The catheter was inserted beneath the transversus abdominis muscle at the lateral edge of its aponeurosis with the linea alba. Each hemiabdomen was injected with either 0.5 mL kg-1 [low volume (LV)] or 1.0 mL kg-1 [high volume (HV)] of a 1:1 mixture of methylene blue 1% and iodinated contrast solution. Three-dimensional reconstruction of tomographic images allowed measurement of injectate spread dimensions. Following dissection, the total number of nerves, their orientation to the incision and extent of staining were determined. The Shapiro-Wilk test and paired t-test were used to compare variables between groups.

RESULTS

Tomographic images confirmed injectate spread within an abdominal fascial plane. Differences were found between groups for total length of spread [HV = 9.93 ± 1.35 cm (mean ± standard deviation); LV = 8.17 ± 1.37 cm; p = 0.002], spread caudal to incision (HV = 3.06 ± 0.88 cm; LV = 1.61 ± 0.97 cm; p = 0.003) and surface area (HV = 26.33 ± 10.08 cm; LV = 19.06 ± 7.54 cm; p = 0.014). The number of nerves stained was 3 (2-4) median (range) in both HV and LV groups. All nerves within the margin of the incision were stained in both groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Both injectate volumes stained all nerves within the margin of the incision. This technique has the potential to provide analgesia to the abdominal wall comparable with an ultrasound-guided TAP block in cats, without the use of specialized equipment.

Open Approach to the Transversus Abdominis Plane in Horses: A Cadaver Feasibility Study

The study's objective was to evaluate the feasibility and dispersion of an open approach to the transversus abdominis plane (TAP) block in eight adult equine cadavers. A ventral midline incision was made, starting 2 cm cranial to the umbilicus and extending 25 cm cranially. In total, 0.5 mL/kg of new methylene blue (NMB) was injected per horse, divided into six injections. Using an 18 g, 8 cm Tuohy needle, three injections were made per side. The needle was guided blindly into the TAP using palpation. A 60 mL syringe was attached directly to the needle, depositing ~0.08 mL/kg at each site. The time to complete the injections was recorded for each cadaver. Following injection, the ventral body wall was dissected to determine if the dye was present within the TAP space as well as to measure the extent of the dispersion of the dye, the cranial to caudal extent, and the width of the dye's spread. Complete deposition of NMB into the TAP (six of six sites) was achieved in 5/8 horses. The median time needed to perform all the injections was 263 s. Increased adiposity (retroperitoneal fat) was associated with unsuccessful injections. This approach to the TAP was easily and quickly performed, though less successful in horses with increased retroperitoneal fat and increased BCS.