Ultrasound-guided transversus abdominis plane block in obese cats: a preliminary cadaveric study

ObjectivesThe aim of the present study was to investigate the distribution of adipose tissue in the abdominal wall of obese cats and compare the injectate spread and spinal nerve staining after ultrasound-guided transversus abdominis plane (TAP) block using lean (LBW) vs actual body weight (ABW).MethodsFour cat cadavers with a body condition score ⩾8/9 were included. Cat 1 was dissected to identify the TAP and describe abdominal fat distribution. Cats 2 and 3 received a two-point ultrasound-guided TAP injection of 0.25 ml/kg/point based on LBW and ABW, respectively. In cat 4, both hemiabdomens were randomly injected with the two volumes. Subsequent anatomic dissection assessed injectate distribution and the number of thoracic (T) and lumbar (L) spinal nerves stained ⩾1 cm circumferentially.ResultsThe mean weight of the cats was 7.5 ± 0.3 kg and they had a body condition score of 9/9. A thick layer of hypoechoic adipose tissue was observed ventral to the costal arch, between the rectus and transversus abdominis muscles, and a second thinner layer between the obliquus internus and transversus abdominis muscles. After crossing the adipose tissue, the ventral branches of spinal nerves lie in the fascial plane, superficial to the transversus abdominis muscle. LBW- and ABW-based injectate volumes stained the ventral branches from T12 to L1 and T11 to L1, respectively.Conclusions and relevanceTwo separate layers of adipose tissues are localized superficially to the transversus abdominis muscle in obese cats. Identifying the transversus abdominis muscle and adipose layers is crucial for the success of the TAP block. Injectate volumes based on ABW may provide wider staining of thoracolumbar spinal nerves than LBW. Further randomized clinical trials are needed in obese cats using locoregional anesthesia.