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

Objective: To evaluate a direct intra-abdominal approach to injection of the ventral transversus abdominis plane (TAP) and compare the dispersion of two volumes of injectate.

Study design: Prospective anatomic and feasibility study.

Animals: A total of 10 canine cadavers weighing 9 ± 4 kg.

Methods: A ventral incision was made extending through the linea alba, from the umbilicus and extending 5 cm caudally. A single injection of an isovolumic mixture of iopamidol and new methylene blue was performed with a hypodermic needle placed within the TAP of each hemiabdomen, alternating between 0.5 mL kg^-1 in low-volume group (LV) and 1 mL kg^-1 in high-volume group (HV). Surgical staples marked the incision. Computed tomography and three-dimensional reconstruction of the tomographic images evaluated the dimensions, cranial and caudal spread beyond the incision and the total area of the injectate. Dissection determined the extent of nerve staining within the TAP adjacent to the abdominal incision. Wilcoxon signed rank (stain) or paired t test was used to compare variables between groups. Data are reported as mean ± standard deviation or median (range).

Results: Injectate spread was within the ventral TAP. Length of spread was 2.5 ± 1.6 cm greater in group HV than in group LV. There was a strong positive correlation between the surface area (p = 0.02, r = 0.71) and cranial-caudal spread of injectate (p = 0.041, r = 0.65) with volume. All but two LV injections were associated with staining of all nerves adjacent to the incision. Additional nerves caudal to the incision were stained in group HV (p = 0.02).

Conclusions: This approach to the TAP was easily performed, with volume of injectate positively influencing distribution.

Clinical relevance: This technique is easily applied and future prospective studies are warranted to determine its analgesic efficacy.