A transverse oblique approach to the transmuscular Quadratus Lumborum block

We congratulate Dr. Elsharkawy for describing a paramedian sagittal oblique (subcostal) approach for the Quadratus Lumborum block 1 that improves visualisation of the muscular, fascial and visceral anatomical landmarks compared with the technique previously described by Shamaan et al. 2. We are also interested in exploring optimal injection techniques for this new block category to achieve consistent injectate spread into the thoracic paravertebral space. We agree with Elsharkawy that a curvilinear transducer provides an excellent field of view, allowing simultaneous visualisation of muscles and fascial planes, the site of injection, intestines and other important intra- and retroperitoneal organs during needle insertion. The transmuscular quadratus lumborum block technique we have described previously 3, 4 uses a curvilinear transducer placed transversely in the mid-axillary line, just cephalad to the iliac crest with the patient in the lateral position. The quadratus lumborum and psoas major muscles and their proximity to the L3 or L4 transverse processes (i.e. the Shamrock sign) are clearly visible and easy identifiable using this approach 3. More recently, we have developed a transverse oblique paramedian approach to the transmuscular Quadratus Lumborum block, with the patient in a sitting position. This technique is particularly helpful when a rescue block is performed after surgery because access to the flank region would be obstructed by surgical dressings and drains (Fig. 1a), making the standard transmuscular Quadratus Lumborum block approach difficult. Unlike Elsharkawy 1, we use the hypoechoic shadow of the transverse processes as the primary proxy endpoint marker for injection (Fig. 1c). The cephalad border of the iliac crest and the spinous processes of the lumbar vertebral column are palpated and marked on the skin (Fig. 1a). A curvilinear transducer 2-5 MHz is placed with a transverse, oblique and paramedian orientation approximately 3 cm lateral to the L2 spinous process. The transverse and oblique orientation of the transducer in the paramedian position is similar to that described for ultrasonographic visualisation of the lumbar paravertebral region 5, 6. If the acoustic shadow of the L2 transverse process cannot be identified in this position, the transducer is first shifted cephalad or caudad to identify the L2 transverse process and the adjoining quadratus lumborum muscle (Fig. 1c). The needle is then inserted in plane from the medial side of the transducer (Fig. 1b) and advanced laterally to enter the interfascial plane between the quadratus lumborum and psoas major muscles (Fig. 1c). With this approach, we think that the psoas major muscle provides a better protective barrier against accidental needle entry into the peritoneal cavity than the thin transversalis fascial layer 1.