We read with great interest the very interesting and thorough article by Petersen et al.1 on the effect of either transversus abdominis plane (TAP) block or local anaesthetic infiltration in inguinal hernia repair. However, we believe that there are some important aspects that need clarification. These are with regard to the choice of technique, knowledge of anatomy and results from previous studies.
Petersen et al.1 found that ultrasound-guided TAP blocks did not reduce postoperative pain after inguinal hernia repair. They mention correctly that local anaesthetic, guided by the aid of ultrasound or anatomical landmarks, is injected into the transversus abdominis fascial plane, wherein the nerves from T6 to L1 are located. Referring to the initial clinical trials by McDonnell et al.2,3 they mention that the analgesic effect of a TAP blockade has been reported to last up to 24 h postoperatively. However, according to their description in the Methods section, Petersen et al.1 performed unilateral ultrasound-guided TAP blocks with the transducer placed transversely in the mid-axillary line between the iliac crest and the costal margin, although it remains clear that McDonnell et al.2,3 performed landmark-based TAP blocks more laterally and posterior at the triangle of Petit. Petersen et al.1 also mention in the Discussion section that they used the ultrasound-guided posterior approach at the umbilical level to perform the TAP block, which they hypothesised might produce a variable involvement of L1. The mentioning of a posterior approach in relation to their mid-axillary ultrasound-guided TAP block is not entirely correct. Thus, the description could be interpreted as somewhat confusing regarding the placement of the TAP blocks.
Using MRI to examine the resulting spread from various truncal blocks, Carney et al.4 found the contrast solution to extend anteriorly to the mid-axillary line inferiorly to the iliac crest and superiorly to the costal margin within the TAP when they performed the landmark-based TAP block, that is double loss of resistance through the triangle of Petit. In addition, Carney et al.4 found contrast enhancement of the paravertebral spaces from T4 at the highest level, to L2 at the lowest level. They also examined the mid-axillary ultrasound-guided TAP block approach and they found that this technique produced a different contrast pattern anteriorly within the TAP. They concluded that the importance of these findings lies in the fact that the associated analgesia was likely to depend on the extent of spread of local anaesthetic within the TAP. It was also concluded that the mid-axillary ultrasound-guided TAP block approach provided for a relatively limited duration of analgesia compared with that resulting from the landmark-based TAP block at the triangle of Petit. Petersen et al.1 correctly comment that the possible superiority of one TAP block technique compared with another remains unanswered.
We have previously published on the time dependent distribution pattern of the injected local anaesthetic resulting from the mid-axillary ultrasound guided TAP block with a similar volume (30 ml ropivacaine 0.375%).5 Using MRI, we found that the local anaesthetic injected with this approach never reached below to the anterior superior iliac spine. Interestingly, even after 6 h following the administration of the blocks, we were unable to detect dermatomal anaesthesia caudad to Th12. Thus, we never achieved dermatomal anaesthesia at the level of L1 with the mid-axillary ultrasound-guided TAP approach.5 Our findings seem to corroborate well with the detailed anatomical descriptions by Rozen et al.6 regarding the L1 branch. Rozen et al.6 described that a main division of L1, the ilioinguinal nerve, always entered the neurovascular plane at the level of the anterior superior iliac spine, consistent with the described literature. Rozen et al.6 performed cadaveric dissections of the anterolateral abdominal wall, and they consistently found the L1 branch at the level of the anterior superior iliac spine and medial to this point, which might well explain the inability of mid-axillary ultrasound-guided TAP blocks to anaesthetise this nerve.
We believe that the best way to produce a consistent block of the L1 in relation to inguinal hernia repair with a mesh using the Lichtenstein technique is to block this nerve selectively guided by ultrasound close to and medial to the anterior superior iliac spine. The injection should be made from the lateral to the medial direction between the internal oblique and the transversus abdominis muscles wherein the L1 nerve branches run with the deep circumflex iliac artery in the neurovascular plane.7 Employing this technique for inguinal hernia repair with a mesh using the Lichtenstein technique, we have previously published results showing a significant reduction in pain scores at mobilisation (P < 0.001) and rest (P < 0.005) recorded in the active (bupivacaine 0.5%) group compared with the placebo group (isotonic saline).7 This significant effect was evident upon arrival in the postanaesthesia care unit and again after 30 min. Pain at rest was similarly reduced in the bupivacaine group at the time of discharge (P < 0.017). Further, in the bupivacaine group, we also reported significantly fewer patients (P < 0.05) with severe (numerical rating scale >5) and moderate (numerical rating scale >3) pain at mobilisation and rest, respectively. Opioid consumption and time spent in the postanaesthesia care unit were not significantly different between groups at any time. In addition, we were unable to detect any significant reduction in pain scores when we conducted telephonic interviews 24 and 48 h postoperatively. It would seem that in order to provide for a more prolonged analgesic effect following inguinal hernia repair, a more posterior approach, as compared with the mid-axillary technique, must be performed to ensure spread of the local anaesthetic to the paravertebral space. Moreover, if a more anterior and medial approach is chosen for this specific surgical procedure, then the direct ultrasound-guided ilioinguinal/iliohypogastric nerve block technique should probably be considered.
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1. Petersen PL, Mathiesen O, Stjernholm P, et al. The effect of transversus abdominis plane block or local anaesthetic infiltration in inguinal hernia repair. A randomised clinical trial. Eur J Anaesthesiol
2. McDonnell JG, O’Donnell B, Curley G, et al. The analgesic efficacy of transversus abdominis plane block after abdominal surgery: a prospective randomized controlled trial. Anesth Analg
3. McDonnell JG, Curley G, Carney J, et al. The analgesic efficacy of transversus abdominis plane block after cesarean delivery: a randomized controlled trial. Anesth Analg
4. Carney J, Finnerty O, Rauf J, et al. Studies on the spread of local anaesthetic solution in transversus abdominis plane blocks. Anaesthesia
5. Børglum J, Jensen K, Christensen AF, et al. Distribution patterns, dermatomal anesthesia and ropivacaine serum concentrations after bilateral dual transversus abdominis plane block. Reg Anesth Pain Med
6. Rozen WM, Tran TM, Ashton MW, et al. Refining the course of the thoracolumbar nerves: a new understanding of the innervation of the anterior abdominal wall. Clin Anat
7. Bærentzen F, Maschmann C, Jensen K, et al. Ultrasound-guided nerve block for inguinal hernia repair: a randomized, controlled double-blinded study. Reg Anesth Pain Med