Description and Evaluation of Dye and Contrast Media Distribution of Ultrasound-Guided Rectus Sheath Block in Cat Cadavers

Simple Summary The rectus sheath block is an ultrasound-guided locoregional anaesthetic technique which aims to provide analgesia to the midline of the abdomen. Previous studies in dog cadavers have shown that the injection of methylene blue within the rectus sheath stained the rami ventrales from T10 to L1, potentially providing anaesthesia to the cranial and middle abdominal midline. We hypothesise that a similar approach would be feasible in cats and could offer equivalent results to those obtained in dogs. For this purpose, ten cat cadavers were included. An iopromide-methylene blue mixture (0.4 mL kg-1) was injected between the rectus abdominis muscle and the rectus sheath. Then, a computed tomography scan and anatomical dissection were carried out to assess the injectate spread. Our results showed a consistent staining of the rami ventrales of several spinal nerves (T11-T12) and frequent staining of T10 and T13. These results are compatible with the supply of somatic anaesthesia in the cranial abdominal midline, although the middle and caudal midline anaesthesia could not be provided.Abstract The rectus sheath block is an ultrasound-guided anaesthetic technique which aims to provide analgesia to the abdominal midline. This study aimed to assess the distribution of 0.4 mL kg-1 of a mixture of methylene blue and iopromide injected into each hemiabdomen in the internal rectus sheath in cat cadavers. We hypothesise that this technique would be feasible and would cover the rami ventrales of the last thoracic and the first lumbar spinal nerves. The study was divided into two phases. Phase 1 aimed to study the anatomical structures of the ventral abdominal wall (four cats were dissected). Phase 2 (ten cadavers) consisted of an ultrasound-guided injection of the mixture mentioned above and the assessment of its distribution by computed tomography and anatomical dissection. The results showed the staining of the cranioventral abdominal wall with a craniocaudal spread of four (three to eight) vertebral bodies. Methylene blue stained three (one to four) rami ventrales, affecting T10 (60%), T11 (100%), T12 (90%), T13 (50%) and L1 (5%). Based on these results, it could be stated that this technique could supply anaesthesia to the midline of the abdominal midline cranial to the umbilicus in clinical patients, but it may not be able to provide anaesthesia to the middle and caudal midline abdominal region.