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

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

Prospective descriptive cadaveric study.

Nine adult feline cadavers.

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.

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.

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.