The retrolaminar block as a regional anaesthetic technique in dogs suffering from thoracolumbar pain

Fascial plane blocks are relatively new regional anaesthetic techniques that rely on the passive spread of the local anaesthetic to the target nerves that are positioned within a fascial plane or in adjacent tissue compartments. There is increasing evidence in the literature for the analgesic efficacy of these techniques but the exact mechanism by which they exert this analgesic effect is unknown. The retrolaminar block is a novel fascial plane block that was developed as a safer alternative to the paravertebral block in humans. When performing the retrolaminar block, the tip of the needle is directed to the lamina of the thoracic or lumbar vertebra of interest, between the dorsal aspect of the lamina and the epaxial muscles. The retrolaminar block has not previously been described in veterinary medicine. The aim of this research thesis was to describe the retrolaminar block in dogs, with the goal of developing it into a new anaesthetic technique to be used as part of a multimodal analgesic regime in dogs that suffer from thoracolumbar pain. Using eight canine cadavers, the first study describes an anatomical landmark-guided thoracolumbar retrolaminar technique. Thirteen retrolaminar injections of iodinated contrast-dye solution were performed at the level of the twelfth thoracic vertebra and the spread of the injectate was evaluated using computed tomography and transverse anatomical dissection. The findings suggest that there was no proportional association between the volume of injectate used and the spread of the injectate, and on all occasions, the injectate spread to the ipsilateral retrolaminar and paravertebral spaces. The second study used ten canine cadavers to develop an ultrasound-guided thoracolumbar retrolaminar technique. The technique was simple to perform, with the relevant sonoatomy easy to visualise and identify. Moreover, the spread of the injectate between the ultrasound-guided retrolaminar injections was compared with the anatomical landmark-guided retrolaminar injections, utilising computed tomography. Even though both techniques were deemed successful with the injectate spreading extensively in the retrolaminar space, ultrasound guidance increased the accuracy of the injections. The third part of the thesis describes the clinical use of the anatomical landmark-guided retrolaminar block in seven client-owned dogs that underwent thoracolumbar spinal surgery. The findings of the above studies encourage future studies investigating the exact mechanism of action of the retrolaminar technique and evaluating its perioperative analgesic efficacy in dogs.