Two-point ultrasound-guided transversus abdominis plane injection in canine cadavers - a pilot study

This study evaluated the spread of a two-point transversus abdominis plane (TAP) injection in canine cadavers. Compared with previous techniques, the two-point TAP injection was developed to increase the consistency of local anaesthetic spread to the nerve segments T11, T12, L1, L2 and L3.

Prospective experimental trial.

Five fresh canine cadavers.

Two-point TAP injections were performed under ultrasound guidance by a single trained individual in canine cadavers (15.7-43.0 kg). Each hemi-abdomen was infiltrated and evaluated independently for a total of 10 evaluations of the technique. The first injection was performed at the level of the costo-chondral junction of the thirteenth rib, and the second injection was performed cranial to the tuber coxae. Each injection comprised 0.3 mL kg^-1 methylene blue solution (0.0015 mg mL^-1). Ten minutes after the injections, abdominal wall dissection was performed, and any nerves stained for a minimum of 10 mm along their long axis were identified and recorded.

During all injections, separation of the internal oblique and transversus abdominis muscles was observed on ultrasound. On dissection, branches of T12, T13, L1, L2 and L3 were adequately stained in 30%, 100%, 100%, 90% and 90% of injections, respectively. No staining of branches of T11 occurred in any of the cadavers. In one hemi-abdomen, branches of L1 and L3, but not L2, were stained.

This study indicates that the two-point TAP injection delivers consistent dye dispersion to adequately stain branches of T13, L1, L2 and L3, with no coverage of T11 and poor coverage of T12, in fresh canine cadavers. An in vivo study using local anaesthetic should be performed to evaluate the analgesic efficacy of this technique in mid to caudal abdominal surgeries.