Novel external oblique muscle plane block for blockade of the lateral abdominal wall: a pilot study on volunteers

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Abstract
Purpose No reports have described techniques to efficiently anesthetize the lateral cutaneous branches of the entire abdomen. The aim of this study was to investigate an effective procedure for blocking the lateral cutaneous branches in the abdominal region. We sought to describe the sensory distribution of the previously described thoracoabdominal nerve block through perichondrial approach (TAPA) and the novel costal and lateral external oblique muscle plane (EXOP) blocks in healthy volunteers. Methods This was a proof-of-concept pilot study that comprised ten volunteers with an American Society of Anesthesiologists Physical Status I. The participants underwent modified TAPA (M-TAPA), injection 2 of TAPA (injection into the anterior aspect of the 10th costal cartilage: I2-TAPA), costal EXOP, and lateral EXOP blocks with injection of 20 mL of ropivacaine 0.2% for each block. A pinprick test was performed one hour after injection and repeated at 30-min intervals until the effect of the nerve block disappeared. Results The M-TAPA injection anesthetized the anterior branches from T6/7 to T11/12, whereas the I2-TAPA injection had no effect. Costal and lateral EXOP injections anesthetized the lateral cutaneous branches of T7–10 and T11–12, respectively. Conclusion The results of this pilot study in ten healthy volunteers indicate that novel EXOP blocks involving local anesthetic injection superficial to the external oblique muscle efficiently anesthetize the lateral cutaneous branches of the thoracoabdominal nerves. Our study shows that it may be anatomically plausible for the combined use of these blocks to anesthetize the entire abdominal wall.

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