Ultrasound-guided injection into the interfascial rectus sheath-associated plane in sheep - a cadaveric study

Abstract

sheep - a cadaveric study Objectives To evaluate ovine anatomy to determine the feasibility of an ultrasound guided interfascial rectus sheath (RS) -associated plane block Study design Prospective, experimental, randomised cadaveric study. Animals A group of 22 fresh cadavers (median 52 kg, range 47–62 kg). Methods In phase I, six cadavers underwent anatomical (n = 2) and ultrasonographic (n 8 = 4) examination of the ventral abdominal wall and RS. Based on these findings, two lateral approaches (one- or two-injections) were defined. In phase II, 14 cadavers were randomly injected bilaterally using the one-injection approach under ultrasound guidance with 0.1% methylene blue at either high (HV, 0.5 mL kg-1 ) or low (LV, 0.25 mL kg-1 11 ) volume, targeting the plane between the rectus abdominis muscle (RAM) and its internal sheath. Dissections evaluated dye distribution and nerve staining Results The one-injection approach provided better visualization and consistent nerve staining. The eleventh thoracic nerve was stained in all cases, while the twelfth (HV = 16 93%; LV = 79%), and thirteenth thoracic nerves were stained only in two cadavers with HV. Dye spread was limited, suggesting compartmentalization of the interfascial plane. 18 Further investigation in two additional cadavers included injections of methylene blue and a neutral red dye (LV each) between RAM and its internal sheath between alternate muscle bellies. The latter injections were within the same unilateral RAM, separated by 21 tendinous intersections. Dissection showed distinct dye accumulation without mixing Conclusions and clinical relevance the described approach produced a limited spread and nerve staining, possibly due to ovine-specific anatomy and the technique employed, which differs from the standard RSB technique. Targeting individual muscular Journal Pre-proof 2 compartments could be an alternative. Further studies using the traditional RSB approach are needed to confirm its applicability in this species