Subcostal Transversus Abdominis Plane Block Under Ultrasound Guidance

To the Editor: Like Shibata et al.,1 I have also found that posterior transversus abdominis plane (TAP) block only reliably produces analgesia below the umbilicus. McDonnell and Laffey2 suggest this is because the local anesthetic spreads progressively over several hours and early assessment may miss this. In a prospective audit of 21 blocks, the distribution of reduced sensation to ice after TAP block as a proportion of the distance from pubis to xiphoid process was 0.52 (0.55–0.48). Of the subset of 12 blocks assessed after a delay of several hours (after spinal anesthesia for cesarean section had regressed), the mean block height was 0.49 (0.45–0.53). There was, therefore, no apparent late spread of the TAP block. I have found an alternative ultrasound-guided technique that I refer to as the “oblique subcostal” TAP block, which can produce reliable analgesia of the supra-umbilical abdomen. A needle of 100 to 150 mm is introduced in plane with a linear ultrasound probe positioned perpendicular to the abdominal wall, directed parallel to the costal margin but oblique to the sagittal plane (Fig. 1). The needle insertion point is near the xiphoid process and the local anesthetic is initially deposited between transversus abdominis and the rectus abdominis muscles, or between the rectus and the posterior rectus sheath if transversus is not behind rectus at that level. The needle is then directed inferolaterally to progressively distend the transversus abdominis plane parallel to the costal margin blocking the intercostal nerves as they emerge to run into the transversus plane. The approach is also suitable for placing a catheter into the plane with the tip near the iliac crest. If a catheter is not planned, two injection points may be technically easier to ensure that local anesthetic is deposited along the plane.Figure 1.: Needle and probe position for oblique subcostal TAP block, area of local anesthetic distribution is shown hatched.In an audit of 20 oblique subcostal TAP blocks, the mean block height assessed by ice as a proportion of the distance from xiphoid process to pubis was 0.86 (0.82–0.90). All blocks were assessed within an hour of placement. Using this approach, there was sometimes sparing of part of the L1 segment at the time of assessment, although no patients had wounds extending to that distribution. Further information on TAP block is available at www.heartweb.com.au Peter Hebbard, MB, BS, FANZCA, P.G. Dip Echo Wangaratta Anaesthetic Group Northeast Health Wangaratta St Vincent's Hospital Melbourne, Victoria, Australia [email protected]