Modified Ultrasound-Guided Dorsal Quadratus Lumborum Block in Cat Cadavers

Abstract

The quadratus lumborum (QL) block is an ultrasound-guided locoregional anesthesia technique which aims to provide analgesia to the abdomen. The main objective of this study was to assess a modified ultrasound-guided dorsal QL block in cat cadavers. For this purpose, a volume of 0.4 mL kg^-1 of a mixture of iopromide and methylene blue was administered between the psoas minor muscle and the vertebral body (VB) of the first lumbar vertebra, and its distribution was assessed in thirteen cat cadavers. We hypothesized that this injection point would be feasible, offering a more cranial distribution of the injectate and a more consistent staining of the truncus sympathicus. The study was divided into two phases. Phase 1 consisted of an anatomical study (three cadavers were dissected). Phase 2 consisted of the ultrasound-guided administration of the injectate and the assessment of its distribution by computed tomography and anatomical dissection. The results showed a consistent distribution of contrast media within five (4-8) VBs from T10 to L5. Methylene blue stained three (2-6) rami ventrales, affecting T11 (10%), T12 (20%), T13 (60%), L1 (85%), L2 (95%) and L3 (65%). The truncus sympathicus was dyed in all cadavers with a spread of five (3-7) VBs. Finally, the splanchnicus major nerve was stained in all cadavers (100%). These results suggest that this technique could provide analgesia to the abdominal viscera and the abdominal wall, probably with the exception of the cranial aspects of the abdominal wall.

Keywords: abdominal analgesia; fascial block; feline; locoregional anesthesia; quadratus lumborum; ultrasound guided.

Figure 1

(A) Ultrasound-guided dorsal approach to the QL block in cat cadavers. Cat cadavers were positioned in lateral recumbency and the transducer positioned transversal to the spine at the L1 level and then rotated 30° cranially. The needle was advanced “in-plane”. (B) Anatomic reconstruction of the ultrasound beam used to perform the approach, avoiding bone structures. QL, quadratus lumborum; Cr, cranial; Cd, caudal; D, dorsal; V, ventral.

Figure 2

Schematic illustration of the L1 region in a cat placed in left lateral recumbency. (A) Classic view of the QL approach. (B) Modified view of the dorsal QL approach. The point of injection is represented by the green circle. Ao, aorta; ES, erector spinae muscles; OEA, obliquus externus abdominis muscle, OIA: obliquus internus abdominis muscle; TA, transversus abdominis muscle; Pm, psoas minor muscle; QL, quadratus lumborum muscle; L1 VB, vertebral body of L1; D, dorsal; V, ventral; L, lateral; M, medial.

Figure 3

Ultrasound images of the modified approach to the QL block in cat cadavers. The needle should contact the vertebral body (green circle), characterized by a hyperechoic line creating an acoustic shadowing. OEA, obliquus externus abdominis muscle; OIA, obliquus internus abdominis muscle; D, dorsal; V, ventral L, lateral; M, medial.

Figure 4

Schematic anatomical view of the region between T11 and L7 vertebrae. T13, L1, L2, L3 rami ventrales of T13, L1, L2 and L3 nerves, respectively. Cd, caudal; Cr, cranial; D, dorsal; V, ventral.

Figure 5

Computed tomographic images in transverse plane at the level of L2 with bone window (A,B) and 3D-VR reconstruction (C) of different cat cadavers after the administration of 0.4 mL kg⁻¹ of a mixture of iopromide and methylene blue at the vertebral body of L1. (A) Contrast can be observed surrounding muscles and within the transversus abdominis plane. (B) Intramuscular spread of iopromide into Pm in the right hemiabdomen is visualized. (C) Volume-rendered three-dimensional reconstruction image of the thoracolumbar area between T12 and L4 vertebrae showing the distribution of the contrast. Pm, psoas minor muscle; D, dorsal; LL, left lateral; RL, right lateral; V: ventral.

Figure 6

Anatomical dissection of the thoracolumbar area stained after methylene blue administration. T13, L1, L2, L3, L4 rami ventrales of T13, L1, L2, L3 and L4 nerves, respectively. Cr, cranial; Cd, caudal; D, dorsal; V, ventral.

Figure 7

Staining of the rami ventrales of the spinal nerves and the truncus sympathicus evaluated by computed tomographic and anatomical dissection after the administration of 0.4 mL kg−1 of a mixture of methylene blue and iopromide by a modified dorsal QL approach. QL, quadratus lumborum block; L, left hemiabdomen; R, right hemiabdomen.