Comparison of Ultrasound-Guided Versus Anatomical Landmark-Guided Thoracolumbar Retrolaminar Techniques in Canine Cadavers

SIMPLE SUMMARY: Ultrasound guidance enables direct visualisation of local anaesthetic spread during the performance of regional anaesthetic techniques, thus improving their accuracy and effectiveness while minimising their complications. In human patients receiving thoracic analgesia, a new regional anaesthetic technique, named retrolaminar block, has a lower complication risk when compared with the gold standard, thoracic paravertebral block. The aim of this study was to develop an ultrasound-guided thoracolumbar retrolaminar technique to provide thoracolumbar analgesia in dogs. Another aim was to compare the distribution of contrast solution between the ultrasound-guided and landmark-guided techniques in canine cadavers, using computed tomography. Ten canine cadavers were randomised to receive either an ultrasound-guided or a landmark-guided retrolaminar injection of 0.6 mL/kg of iodinated contrast solution in each hemithorax at the level of the twelfth thoracic vertebra. The injectate spread in a similar manner in the retrolaminar space and the space surrounding the intervertebral foramina, while minimal spread was noted in the paravertebral space. One of the landmark-guided injections failed to spread, thus highlighting the importance of ultrasound guidance in improving outcomes in regional anaesthetic techniques. Further studies are warranted to clarify the role of the ultrasound-guided retrolaminar technique in the management of thoracolumbar pain in dogs. ABSTRACT: The retrolaminar block was developed in humans as an easier and safer alternative to the thoracic paravertebral block. This study aims to describe an ultrasound-guided thoracolumbar retrolaminar injection in canine cadavers and compare the injectate distribution between a landmark-guided and an ultrasound-guided thoracolumbar retrolaminar technique using computed tomography. Ten canine cadavers were randomised to receive two injections each of 0.6 mL/kg of iodinated contrast at the level of the twelfth thoracic vertebra (T12): a landmark-guided retrolaminar injection was performed on one hemithorax (group B, n = 10) and an ultrasound-guided on the other hemithorax (group U, n = 10). Groups were compared using the Mann–Whitney U test. The median (range) spread of the contrast in the paravertebral space was 0 (0–3) and 1 (0–5) vertebrae in groups B and U, respectively (p = 0.038). The median (range) extent of the spread surrounding the interverbal foramina was 4 (0–5) in group B and 4 (3–5) in group U. The median (range) spread along the retrolaminar space cranial and caudal to T12 was 3 (0–6) retrolaminar segments in group B and 3 (3–4) in group U. The potential of the ultrasound-guided retrolaminar injection to provide analgesia for dogs suffering from thoracolumbar pain should be further investigated.