Two-point rectus sheath block technique results in more extensive dye spread in the abdominal wall than one-point...

To develop a two-point rectus sheath block (RSB2) and assess the staining of ventral branches of spinal nerves following this approach compared with a previously described single-point rectus sheath block (RSB).

Prospective, randomized experimental cadaveric study.

Eight dog cadavers (10.9 ± 1.5 kg, mean ± standard deviation).

Each dog underwent both techniques assigned randomly to right or left hemiabdomen. Equal volumes of methylene blue (1%) were used per hemiabdomen (RSB: 0.5 mL kg^-1, RSB2: 0.25 mL kg^-1 per injection site with a total of 0.5 mL kg^-1). For RSB, the transducer was placed transverse to midline and 1 cm cranial to the umbilicus. For RSB2, a cranial injection was performed with the transducer parallel to the costal arch. For the RSB2 caudal injection, the transducer was placed as in RSB, but 2 cm caudal to umbilicus. All injections were performed using an in-plane technique with a lateral-to-medial needle orientation. Dissections were performed to assess the extent of dye spread with each technique and compared with a Mann-Whitney test.

More ventral branches of spinal nerves were stained in RSB2 than RSB [6 (5-7) and 4.5 (4-6), respectively; p = 0.023, 95% confidence interval = 0-2]. The greater dye distribution in the RSB2 was preferentially cranial to umbilicus (p = 0.025, 95% confidence interval = 0.4-5.5). The incidences of thoracic (T) and lumbar (L) nerve staining following RSB and RSB2 techniques were, respectively: T9 (12.5% and 25%), T10 (25% and 75%), T11 (50% and 100%), T12 (100% and 100%), T13 (100% and 100%), L1 (100% and 100%), L2 (87.5% and 75%) and L3 (0% and 25%).

RSB2 resulted in more extensive abdominal dye spread, especially cranially, compared with RSB using the same total injectate volume.