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As an original author of this block [1], I have watched with great interest all the developments and changes that have taken place over the last decade. In my opinion, many of those techniques, including some ultrasound approaches, have deviated from the original concept, resulting in contradictory results from different clinical trials or methods [2, 3]. Recently, the practice of blind transversus abdominis plane (TAP) block has been questioned [4] based on an unacceptably high reported incidence of intraperitoneal injection, which has prompted me to defend this landmark-based approach as simple, safe and effective.

In my original description, a single ‘pop’ sensation served as an endpoint for appropriate needle depth. In this technique, there is more emphasis on identifying the iliac crest and recognising the point or angle where latissimus dorsi is attached to the external lip of iliac crest forming the posterior border of the lumbar triangle, which I call the latissimo-iliac point (LIP). The LIP is an easily identified and consistent landmark in most individuals. The iliac crest [5] has ventral and dorsal segments. The ventral segment has external and internal lips and a rough intermediate zone. The lower fibres of the external oblique and the latissimus dorsi muscles are attached to the external lip. A variable interval exists between the most posterior attachment of external oblique and the most anterior attachment of latissimus dorsi. Here, the crest forms the base of the ‘lumbar triangle of Petit’. The floor of the triangle is the internal oblique muscle, which is attached to the crest's intermediate area. The transversus abdominis muscle is attached to the anterior two thirds of the crest's inner lip.

I feel compelled to go over my single ‘pop’ technique once again in order to emphasise the importance of identifying the LIP. After identifying the LIP, I immobilise the skin against the bony crest with one or two fingers. I insert my needle within the lumbar triangle just anterior to the LIP and advance it until contact with external lip of the iliac crest is felt, at which point, the needle tip is already through the fascial extension of the external oblique muscle. From this point, I walk my needle over the intermediate zone (top) of the iliac crest until I feel a definite ‘pop’ or sensation of giving way. This ‘pop’ is unmistakable once experienced and signifies traversal of the needle tip through the insertion of internal oblique muscle. At this juncture, the needle tip has reached the target plane between the internal oblique and the transversus abdominis muscles where local anaesthetic agent is to be deposited. I usually insert my needle perpendicular to the skin but in obese patient, I advance it slightly caudad to make sure I do not miss the iliac crest. I change the needle direction once the bony crest is localised; otherwise, there is a possibility of going all the way through the abdominal wall. Identifying the LIP and localising the bony crest's external lip is of utmost importance in successful and safe performance of this technique. For reasons given above, I am inclined to call my technique ‘LIP’ block instead of ‘TAP’ block.

In my experience, the LIP block is more successful than ‘double pop’ technique [6-9] and ultrasound-guided approaches [10, 11] described in the literature. The LIP is invariably localised posterior to the mid-axillary line, which is important due to the dual nerve supply of the abdominal wall. An intercostal nerve enters the plane between the internal oblique and transverse abdominis muscles (also known as the TAP), before emitting a lateral cutaneous branch at the mid-axillary line, the anterior division of which runs in the external oblique plane (EOP) between skin/subcutaneous tissue and the external oblique muscle. For any approach to be successful, whether ultrasound-guided or landmark-based, the nerves must be blocked in both the TAP and the EOP, or at (or proximal to) the origin of the lateral cutaneous branch. Any deviation from this principle will result in a partially effective and unsatisfactory block. In the last few years, a variety of ultrasound-guided approaches with variable results have been described to overcome this problem. So far there is no consensus on the best possible approach that signifies the difficulties and limitations of this block.

An anatomical study [12] by Jankovic et al. on 26 cadaveric specimens found that the lumbar triangle of Petit varies in angle, shape and size between individuals, making its identification difficult by palpation alone. McDermott et al. [4] found unacceptably high levels of intraperitoneal needle placement and concluded that needle and local anaesthetic placement using the standard landmark-based approach to the TAP block is inaccurate. They used the landmark-based ‘double-pop’ method which was a modified version of the ‘single-pop’ method described by me in 2001 [1]. McDonnell et al. reported it as the ‘R.A.F.I. technique’ in 2004 [6] and O'Donnell et al. renamed it as the TAP block in 2006 [7]. According to their technique, the needle is inserted cephalad to the iliac crest within the lumbar triangle and advanced until two distinct ‘pops’ are felt. McDonnell et al. state that the success of the block relies on the point of needle insertion through the apex of the lumbar triangle [13]. I think the ‘double-pop’ technique described by McDonnell et al. is fraught with many technical flaws. Firstly, given so much variation in size, shape and angles of the lumbar triangle, one cannot be sure about the apex of the triangle, let alone the position and path of the needle. It is hard to know if the needle is going through the external oblique muscle outside the triangle or its fascial extension within the triangle. There is also a possibility that the needle has pierced the latissimus dorsi muscle accidentally. In my experience, the ‘pop’ felt when the needle goes through the fascial extension of the external oblique muscle within the triangle is very subtle and could be easily missed. If a ‘double-pop’ is being sought, one can easily end up penetrating the peritoneum, when the second ‘pop’ results from penetration of the transversus abdominis muscle. Secondly, with the ‘double-pop’ technique, one cannot gauge the position of the needle relative to the anatomical structures in its path. With different patient sizes and attendant variations in depth of the triangle, it is difficult to standardise an approach that could be easily followed by every practitioner producing comparable or similar results.

In contrast, the LIP block is based on identification of the LIP, which is easily palpable in most patients. The path and position of inserted needle is apparent throughout the entire procedure since the needle is walked over top of the crest, and, passing through the insertion fibres (osseous-muscle interface) of the internal oblique muscle, ellicits an endpoint ‘pop’ that is unique and cannot be easily missed. In elderly or lean individuals, the whole thickness of the iliac crest can be grasped between two fingers, giving the practitioner a good estimate of the safe depth of the needle placement, as the needle tip must not be advanced beyond the inner lip of the crest. Positioning the patients semi-laterally with a wedge support during the block makes the procedure easier to administer, and increases its safety margin by moving the abdominal viscera away from the site of block.

In my opinion, the LIP block is a simple bedside procedure that not only can be performed in the operating room or recovery area, but also can be repeated on demand for rescue analgesia. It would be premature to reject a useful blind procedure on the basis of one study that has chosen a technique described specifically for use under ultrasound guidance. Until we are able to define the best possible ultrasound-based approach, the landmark-based technique should continue to be taught and administered.

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