Maximum extension and regression rate of cutaneous sensory block obtained with the external oblique intercostal block or the modified thoracoabdominal nerves block through perichondrial approach in patients undergoing laparoscopic cholecystectomy.

Background: Several studies demonstrate that both external oblique ıntercostal block (EOIB) and modified thoracoabdominal nerves block through perichondrial approach (M-TAPA) contribute to analgesia in the anterior abdomen by targeting the thoracoabdominal nerves through distinct pathways. However, the sensory assessment and dermatomal analysis remain poorly understood.

Methods: This prospective observational study aimed to determine the sensory assessment and dermatomal regression rate of EOIB and M-TAPA in patients undergoing laparoscopic cholecystectomy. The study included a total of 24 patients, with 12 patients in each group. Blocks were performed bilaterally, administering 25 mL of bupivacaine 0.25% for each side, resulting in a total volume of 50 mL. The anterior abdominal wall was vertically partitioned into the midabdomen, left-lateral abdomen, and right-lateral abdomen, and horizontally divided into the epigastric, umbilical, and hypogastric regions. Sensory block was assessed at the 45^th minute with cold stimulus and pinprick. Subsequent evaluations were at intervals of 6, 10, 14, 18, 22, and 24 hours.

Results: The blocked area percentile with cold sensation in the anterior abdomen was 43.07% (36.67-55.74) with EOIB, 40.49% (34.05-43.67) with M-TAPA (P=0.3219). When the region above the intertubercular plane was examined with cold sensation, EOIB covered 55.92% (46.75-62.07), and M-TAPA covered 49.60% (40.39-54.03) of the epigastric and umbilical areas. Assessment of the midabdominal portion of the anterior abdomen revealed that the blocked area percentile was statistically significantly higher in the M-TAPA group with both cold sensation and pinprick. At 45 minutes, the percentage of blocked dermatomes was 100% between T7-T8 in the EOIB group and between T7-T10 in the M-TAPA group. Both groups exhibited lower success rates in dermatomes T5 and T12, with no sensory block within the L1 dermatome, and cutaneous dermatomal block status either absent or negligible after 24 hours. All trocar entries were located within the cutaneous sensory block for both blocks, except for trocar C, which was located most laterally.

Conclusions: Bilateral EOIB and M-TAPA produce a comparable sensory cutaneous block in the anterior abdomen, particularly in the umbilical and epigastric regions. Additionally, the midabdominal cutaneous blocked area was greater in patients undergoing M-TAPA, suggesting a more consistent distribution along the anterior cutaneous branches of the thoracoabdominal nerves.