Combined caudal retrocostal and lateral ultrasound-guided approach for transversus abdominis plane injection: A descriptive pilot study in pig cadavers

Abstract

Transversus abdominis plane (TAP) block is a regional anesthetic technique used to desensitize the abdominal wall in several species. This study aimed to describe the anatomical characteristics of the abdominal wall and to identify a feasible approach for an US-guided TAP injection that would result in adequate staining of the relevant nerves in the abdominal wall in pig cadavers. Fresh cadavers from five Landrace pigs (age, 12 weeks; body weight, 35.5 ± 1.6 kg) were used. One pig (n = 1) was anatomically dissected, and four pigs (n = 4; i.e., 8 hemiabdomens) were used for TAP injections and evaluation of dye spread. The volume of 0.3 mL/kg/injection point of methylene blue was injected bilaterally. In the caudal retrocostal approach, the injection was performed ventral to the most caudal part of the costal arch. In the lateral approach, the injection was performed between the last rib and iliac crest. A needle was inserted in plane for the caudal retrocostal and the lateral approach caudocranially and craniocaudally, respectively. Successful staining was defined as presence of dye on the nerve for a length of >1 cm in its entire circumference. The TAP was found between different muscle layers in the described anatomical regions. In the caudal retrocostal approach the TAP was found between the external abdominal oblique and transversus abdominis muscle bellies. In the lateral approach the TAP was found between the internal abdominal oblique and transversus abdominis muscles. The approach combining lateral and caudal retrocostal injections at the studied volume stained a median of 5 (3–6) target nerves from the fourth-last thoracic nerve to L2 (six nerves). Combined caudal retrocostal and lateral TAP injections of 0.3 mL/kg/injection point, resulted in staining of target nerve branches which supply the periumbilical and caudal abdominal wall in pig cadavers.

Anatomical Differences in the Abdominal Wall Between Species with Implications for the Transversus Abdominis Plane Block

“…Yet, because the number of vertebrae shows high variability across species, the specific nerves that will travel and innervate the abdominal wall varies. In mammals, the abdominal wall is typically innervated by the lower thoracic nerves and the upper lumbar nerves, although in some species this can extend to include the sacral nerves as well [31][32][33]. In birds, the number of nerves innervating the musculature and overlying skin of the abdominal wall is reduced.…”

“…For instance, dogs, cats and rats exhibit a 13 th rib that is absent in humans which serves as an attachment site for the abdominal muscles [11,[46][47][48][49]. This is again seen in pigs with 15 to 17 ribs and horses who have 18 ribs [31,38].…”

“…Furthermore, given the variable number of thoracic and lumbar vertebrae among mammals, the number of spinal nerves innervating the abdomen is also variable. The abdominal wall in pigs receives innervation from spinal nerves approximately originating from T6 to L3 and that of horses receives innervation between T5 to L2 [31,38]. However, given the increased number of thoracic vertebrae among pigs and horses (15 to 17, and 18 respectively), this comprises many more nerves than that is observed in humans [31,38].…”

Use of subcostal and lateral transverse abdominal plane blocks as part of multimodal analgesia in a calf undergoing omphalitis surgical correction

“…The ultrasound (US)-guided transversus abdominis plane (TAP) block is a well-established local anaesthetic technique in veterinary medicine [3][4][5][6][7][8][9][10][11] that can desensitise the sensory afferent innervation of the surgical site for median celiotomy and abdominal wall surgery. The use of US-guided TAP block has been reported in calves.…”

Ultrasound‐guided modified subcostal transversus abdominis plane block in a foal undergoing omphalectomy

“…In veterinary medicine, this block has been described in the cadavers of dogs, calves, ponies, horses and pigs (Baldo et al., 2018; Bruggink et al., 2012; Calice et al., 2021; Drozdzynska et al., 2017; Freitag et al., 2021; Mirra et al., 2018; Schroeder et al., 2011).…”