Assessment of an Ultrasound-Guided Rectus Sheath Block in Foals: A Cadaveric Study

Simple Summary Foals are commonly subjected to surgeries related to umbilical pathologies. Due to side effects of systemic analgesics and the immaturity of their organ systems, it is challenging to provide adequate analgesia. It is in this context that the role of regional anaesthesia allows for the provision of good quality analgesic coverage, reducing the potential complications associated with systemic analgesic drugs such as opioids. Ultrasound-guided locoregional techniques are commonly employed in both human and veterinary medicine to provide accurate, safe, and effective analgesia in the regions of interest. The rectus sheath block provides adequate analgesia in procedures involving the umbilical area in humans and has been described in other species, including dogs, pigs, calves, and lately in adult horses. The aim of this study was to describe an ultrasound-guided periumbilical rectus sheath block in foal cadavers and evaluate the spread of the contrast media injected. The results obtained indicated that this approach could provide analgesia around the umbilical area due to the nerves stained. However, further studies evaluating the clinical efficacy of the rectus sheath block are necessary.Abstract In neonatal equines, pathologies involving umbilical structures are an important cause of morbidity, and surgical removal of urachal remnants is a common procedure in clinical practice. Surgery involving the ventral abdominal wall can cause substantial pain, leading to complications and prolonged recovery. The objectives of this study were to describe a two-point bilateral ultrasound-guided rectus sheath block at the level of the umbilicus and to evaluate the extent of dye distribution in foal cadavers. Ten foal cadavers were included in the study, in which a bilateral two-point ultrasound-guided rectus sheath block was performed-one injection 5 cm cranially and a second one 5 cm caudally to the umbilicus. The injectate consisted of a mixture of iodinated contrast medium and blue dye at a volume of 0.25 mL kg-1 per injection point (total 1 mL kg-1). After the injection, computer tomography and subsequent dissection of the ventral abdominal wall were performed. The extension of the contrast medium, the number of stained nerves, and contamination of the abdominal cavity were evaluated. The cranio-caudal extension of the contrast ranged from 0.8 to 1.4 cm per milliliter of injectate. The most commonly stained ventral branches of spinal nerves were thoracic (Th) nerves 16, 17, and 18 (95%, 85%, and 80% of the nerves, respectively). Abdominal contamination was found in four animals. The results suggest that the block could provide periumbilical analgesia. Further studies with different volumes of injectate and living animals are warranted.