Assessment of an ultrasound-guided technique for catheterization of the caudal thoracic paravertebral space in dog cadavers

Background: The caudal thoracic paravertebral (CTPV) block is a regional anaesthesia technique currently used in human medicine to provide analgesia in abdominal surgical procedures Aim: The objectives of this study are to describe an ultrasound-guided technique to place catheters in the caudal thoracic paravertebral (CTPV) space in canine cadavers and evaluate the distribution of a 50:50 contrast-dye solution administered through them. Methods: Eight thawed adult beagle cadavers (9.2 ± 2.0 kg body total weight) were used. Thirteen catheters were placed. In a first phase a volume of 0.3 mL kg-1 of the contrast-dye was administered in all cases. After the injections, computed tomography (CT) scans were carried out to assess the distribution of the contrast-dye. In a second phase, extra 0.2 mL kg-1 of the contrast-dye was administered through 8 catheters, followed by a second CT scan. Two cadavers were dissected to assess the distribution of the contrast-dye. The injection site varied between T8-9 and T12-13. Results: The evaluation of the CT scans showed contrast-dye within the paravertebral space in 92% (12/13) of the injections. The distribution pattern observed after the injections performed within the TPV space was linear and intercostal in all cases. The median (range) linear spread of the contrast was 7 (5-10) spinal nerves and involved 3 (2-8) intercostal spaces. The contrast-dye reached lumbar regions in a 42% of the injections (5/12). A larger spread of the contrast-dye was not observed after the administration of a second dose of the injectate. No signs of epidural, intrapleural/intrapulmonary, intravascular or intraabdominal spread were observed. The dissection of the two cadavers confirmed the spread of the contrast-dye along the sympathetic trunk and intercostal spaces. Conclusion: The administration of 0.3 mL kg-1 of the contrast-dye in the CTPV space resulted in a distribution compatible with the block of nerves responsible for the innervation of the majority of the abdominal viscera and cranial abdominal wall