Ultrasound-guided transversus abdominis plane block in sheep : a descriptive cadaveric study of a three-point injection technique

Development in veterinary anaesthesia and analgesia has led to prioritization of perioperative patient comfort. Surgeries involving an incision in the abdominal wall are considered very painful, so use of opioid drugs and/or loco-regional anaesthetic techniques is often implemented for such procedures. The transversus abdominis plane (TAP) block was developed to provide sensory analgesia to the ventral and lateral abdominal wall. It is a technique involving injection of local anaesthetic into the neurovascular plane between the transversus abdominis and internal oblique abdominal muscles, aiming to desensitize the ventral branches of the thoracic and lumbar nerves involved in the innervation of the ventrolateral abdominal wall, thus contributing to overall reduction in opioid use for perioperative pain management. Numerous studies on the TAP block have been conducted both in human medicine and in several species in veterinary medicine, however no research to date has been published on the TAP block in sheep, animals often used as experimental research models. Therefore, the objective of this thesis was to describe an ultrasound-guided three-point TAP block approach in this species. The study was conducted on sheep cadavers and a three-point injection technique was performed, following an anatomical study used to determine appropriate injection points. The results obtained in the study showed adequate dye dispersion and staining of the thoracic nerve branches of T9, T10, T11, T12 and T13 and lumbar nerve branches of L1 and L2. These results suggest a great potential for the use of TAP block in sheep to provide excellent sensory blockage to a large area of the abdominal wall following a combination of the three injection points. This study represents a remarkable first step into the development of the TAP block in sheep, however further research is warranted to determine the adequate settings for performing this technique in living sheep and to evaluate its perioperative analgesic efficacy for clinical use.