Subcostal TAP block: one or two sequential injections? A cadaveric study.

Background and objectives: The subcostal transversus abdominis plane block (scTAPB) provides analgesia to the anterior abdominal wall but analgesic spread following a single injection remains modest and variable. The oblique scTAPB, which is performed with a continuous injection during needle progression into the TAP along the oblique subcostal line, may extend the block to the whole anterior abdominal wall but needle progression by hydrodissection may be difficult, explaining why this block is not widely used. This study investigated if two sequential scTAPB injections (2scTAPI) may reach more nerves than a single scTAPB (1scTAPI).

Methods: After institutional approval and under ultrasound guidance, a single injection of 20 mL of blue dye was performed in 16 cadaveric subjects into the TAP along the costal margin and lateral to the semilunaris line (1scTAPI). On the opposite side, a 20 mL of green solution was split into two injections (2scTAPI), using one injection medial and one lateral to the semilunaris line. Dye spread was assessed via gross anatomical dissection using an indirect method to quantify the involvement of the anterior cutaneous branches of the intercostal nerves with each technique. A nerve was considered stained if the dye was observed in the TAP, reaching the costal margin aligned with the bony extremity of its corresponding rib.

Results: According to the spread to the costal margin, the estimated median number of consecutive nerves reached by dye after 2scTAPI was 5 (IQR 5-6) vs 3 (IQR 3-4) for 1scTAPI (p=0.00001). Spread after 2scTAPI suggested coverage of nerves originating from T8 to T12 in 85% of the subjects, and from T7 to T12 in 5 out of 17 cases. Spread following the 1scTAPI suggested coverage of nerves from T9 to T11 in most cases.

Conclusions: In a cadaveric model, a larger spread at the costal margin was obtained after 2scTAPI, suggesting a greater coverage of anterior branches of abdominal wall nerves compared with 1scTAPI. Clinical studies are needed to confirm these results.