Yet more on TAP block nomenclature

We read with interest the letter from Hebbard regarding TAP block nomenclature 1. We wish to make some comments, hoping to not add confusion to the discussion. The nomenclature regarding TAP block was initially based on topographic descriptions of where to access the block superficially in the abdomen (anterior, posterior, lateral, mid-axillary, subcostal, etc). Over time, nomenclature came to include the deep anatomy of the transverse abdominal plexus, as highlighted by Borglum et al. 2, and also the ‘target’ area of TAP block 2. We believe that an upper (intercostal) and lower TAP block can be based reasonably on anatomic findings 2, 3 and spread pattern of anaesthetic 2, and that correct nomeclature should be based primarily on these rather than the injection site, particularly as several anatomic studies, together with our own clinical experience with ultrasound, have shown that superficial anatomy does not reflect deep anatomy, which is the ‘target’ of TAP block 3, 4. For this reason, the ‘upper subcostal TAP block’ defined by Hebbard should be called an ‘upper rectus sheath block’, because it aims to block the rectus sheath plexus. Moreover, the anatomic basis for the classification of the subcostal TAP block into an ‘upper’ and ‘lateral’ TAP block or a ‘medial’ and ‘lateral’ intercostal TAP block, as named by Borglum et al., has to be demonstrated on the basis of anaesthetic spread, nerve involvement and dermatomal anaesthesia 5. The term ‘ilio-inguinal TAP block’ is acceptable, but only if performed as described by Hebbard because all the other lower TAP block techniques may unreliably block the L1 roots 1. Anatomical, imaging and clinical studies show a different pattern of anaesthetic spread, nerve involvement and dermatomal anaesthesia between access sites for TAP block 6. This is true expecially for lower TAP blocks (mid-axillary, posterior, triangle of Petit, lateral, anterior, classic, etc). For this reason, we think that nomenclature should include a secondary indication of expected block coverage. However, a great variability in anaesthetic spread, nerve involvement and dermatomal anaesthesia is seen after TAP blocks. For example, regardless of the dual technique and a relatively broader area of block after subcostal TAP block 5, 7, efficacy seem to be greater in the lower abdomen 5, with the mean number of affected nerves limited to 3.75 after lower TAP block 8 and 5.5 after upper TAP block 8, corresponding clinically to the mean number of dermatomes blocked 2, 6, 9. Carney et al. showed also epidural and paravertebral extent of anaesthetic related to some techniques 4. Deeper knowledge of the spread pattern and the expected area of dermatomal coverage are needed before nomenclature can be modified correctly.