Images in Anesthesiology Practical tips for placement of transversus abdominis plane catheter using oblique subcostal approach

Distribution of the sensory block produced by a lateral transversus abdominis plane (TAP) block is narrow and scattered, and not consistent with a dermatoma pattern.1 Shortcomings of the procedure prevent a widespread sensory block provided by the TAP blocks. The anterior branches of the spinal nerves run immediately superficial to the transversus abdominis muscle, forming a plexus. Hence, if local anesthetics are not delivered under the fascia between either the internal oblique or the rectus abdominis muscles and the transversus abdominis muscle, they may only affect the nerves penetrating the fascial layer, resulting in a scattered distribution of blockade.1 A plexus of nerves with extensive communication within the TAP may also explain the non-dermatomal sensory block spread by the TAP blocks. Furthermore, Børglum et al. hypothesized that local anesthetics infused into the TAP, medial and lateral to the linea semilunaris, did not communicate with each other. Moreover, with the injection of local anesthetics into the TAP beneath the aponeurosis of the linea semilunaris, we sensed a higher opening pressure compared with hydrodissection of the other parts of the TAP. We believe that an oblique subcostal approach originally reported by Hebbard et al. can address these issues. With the oblique subcostal approach, local anesthetics are first injected into the TAP near the xiphoid process, where the TAP is determined between the rectus abdominis and transversus abdominis muscles. Further, the needle is advanced along the line connecting the xiphoid process and the anterior border of the iliac crest (i.e., the oblique subcostal line), beyond the aponeurosis of the linea semilunaris, while hyrdodissecting the TAP with incremental injections of local anesthetics. The oblique subcostal line crosses the tracks of the spinal nerves derived from T7 to L1 roots. Using a 15e20 cm long needle and 30e50 ml of the local anesthetics enables hydrodissecting the unilateral TAP along the entire oblique subcostal line, avoiding re-insertion of the needle.