Sensory Assessment and Regression Rate of Bilateral Oblique Subcostal Transversus Abdominis Plane Block in Volunteers

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Abstract
The analgesic effect and duration of a transversus abdominis plane (TAP) block remain controversial. Transversus abdominis plane blocks are effective for somatic/incisional pain but do not provide analgesia for visceral pain from intra-abdominal procedures. The purpose of this study was to assess the area and extent of cutaneous sensory blockade and the regression of dermatomal anesthesia after bilateral oblique subcostal TAP block. This observational, prospective clinical study consisted of 12 healthy volunteers. All volunteers received a bilateral oblique subcostal TAP block under real-time ultrasound guidance with 20 mL of 0.375% ropivacaine. The anterior abdominal cutaneous area was divided into 3 parts (midabdomen, left-lateral abdomen, right-lateral abdomen) using 2 lines drawn in a parasagittal fashion 5 cm lateral to the midline. The area of cutaneous sensory blockade involving the anterior abdomen was assessed 30 minutes after institution of the block using a cold stimulus. This was followed by repeated measurements using a cold stimulus applied along parasagittal lines drawn 3 cm lateral to the midline at 0.5, 6, 10, 14, 18, 22, and 26 hours after blockade. The area of cutaneous sensory blockade of the abdomen was 332 (SD, 73) cm2; that of the midabdomen was 253 (SD, 29) cm2, which represented an average of 90% of the area of the midabdomen; and that of the lateral abdominal wall (combination of left-lateral abdomen and right-lateral abdomen) was 79 (SD, 62) cm2, which represented an average of 26% of total lateral abdominal area. Dermatomes T7–T12 of the midabdomen were successfully blocked in all volunteers after using the bilateral oblique subcostal technique. However, T6 and L1 were only variably blocked. The area of cutaneous sensory block of the anterior abdomen regressed over the ensuing 22 hours in the following manner: 90%, 87%, 73%, 50%, 22%, 3%, and 0% at 0.5, 6, 10, 14, 18, 22, and 26 hours, respectively. Bilateral oblique subcostal TAP block produces a widespread cutaneous sensory blockade with a consistent dermatomal distribution in the midabdomen for a considerable effective duration.

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