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Department of Anaesthesia; Clinical Sciences Institute; Galway University Hospitals; Galway, Ireland; john.laffey{at}nuigalway.ie
In Response:
Dr. Reid (1) makes two points. The first concerns the anatomy of the triangle of Petit. Dr. Rafi (2), an early collaborator with the first author (JMcD) in developing this block, was incorrect in stating that the floor of the triangle is formed by the internal oblique muscle. As stated in our original paper, the floor of the triangle of Petit is made up of fascial extensions of the external and internal oblique muscles (3). The needle does not traverse the external oblique muscle, but rather the fascial extensions of this muscle and the internal oblique. It is these fascial layers which produce the "pop" sensation described when performing the block. The needle then lies just lateral to the transversus abdominis, which is the correct position for the performance of the block. We are currently further characterizing the anatomy of the transversus abdominis plane block in cadaveric studies.
The second point concerns the performance of the block in obese patients. We acknowledge that the triangle of Petit can be more difficult to locate in these patients. However, we have a high success rate with the block even in this group. However, we do recommend initially performing this block in patients with a normal body habitus, in order to gain experience with the block prior to moving onto patients that one might find more challenging. A number of maneuvers may aid palpation of the triangle in these patients. There is usually tenting of the adipose tissue at the pelvic rim, so that this adipose fold can be "displaced" superiorly. Palpation can be further aided by having the patient lift their head off the bed which tenses the abdominal wall and makes the triangle easier to palpate. It is also worth remembering that palpation of the triangle of Petit can cause some discomfort, which can be used to confirm the location of the triangle. We are currently characterizing the utility of ultrasound, which may aid the location of the triangle, particularly in obese patients.
We agree with Dr. Tornero-Campello (4) that the clinical utility of the transversus abdominis plane block can usefully be compared to epidural analgesia. We wish to clarify that there is currently no reason to contend that the transversus abdominis plane block would provide superior analgesia to epidural blockade, and have not made this claim. As discussed in our paper, there are many patients undergoing abdominal surgery for epidural blockade is not available, due to contraindications such as sepsis or coagulopathy or to logistical issues such the lack of availability of the required postoperative monitoring. Therefore epidural analgesia cannot be considered "standard care," but rather is the ‘gold standard’ for provision of postoperative analgesia. Furthermore, the transversus abdominis plane block can provide unilateral analgesia, an advantage in patients undergoing non-midline abdominal incisions. In our study, we demonstrated that the transversus abdominis plane block substantially improves patient comfort when compared to patients who receive opioid-based postoperative analgesia. Therefore, at present we would recommend the transversus abdominis plane block for patients in whom epidural analgesia is not feasible for the reasons discussed earlier.
REFERENCES
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