Ultrasound guided quadratus lumborum block in swine: a pilot evaluation by computed tomography of the spread of two injectate volumes

The ultrasound (US) guided quadratus lumborum (QL) block is an interfascial plane block performed in humans and animals to provide abdominal wall and visceral analgesia perioperatively. The aim of the study was to evaluate the spread of a ropivacaine-dye solution after a QL block in Göttingen minipigs. Two adult Göttingen minipigs undergoing a computed tomography (CT) evaluation as part of an experimental procedure were considered. Under general anesthesia an US evaluation was performed with the animals in sternal recumbency to identify the transverse process of L2, the longissimus dorsi and the QL muscles, and the interfascial plane between the QL and the psoas maior muscle. A QL block was performed with the US probe parallel to the ribs by injecting ropivacaine 0.3 % dye solution between the transverse process of L2 and the interfascial plane. The four hemiabdomens randomly received 0.3 or 0.5 mL/kg injectate. The spread of the solution was evaluated by a CT scan. The animals were euthanised at the end of the evaluations. The solution spread between the QL and the psoas maior muscles in all but one hemiabdomen in which an intramuscular staining was observed (0.5 mL/kg injection). The solution spread from L1 to L6 for the 0.3 mL/kg injection and from L2 to L5 for the 0.5 mL/kg injection. In conclusion this approach for the QL block might not result in spreading to the sympathetic trunk in minipigs while potentially affecting pelvic limb innervation. The analgesic efficacy of this technique is to be evaluated.