A New Approach to Ilio-inguinal Nerve Blocks: 3-layer Injection vs Conventional Ultrasound-guided Single-shot Approach

Project Summary Rationale - The conventional technique for performing an ilio-inguinal nerve block involves a single shot of local anesthetic (usually 0.3 mL/kg of 0.25% bupivacaine) in the transversus abdominis plane of the anterior abdominal wall. Using a blind technique (also known as "fascial click"), a blunted needle (20 gauge) is placed 1 cm medial and 1 cm inferior to the anterior superior iliac spine (ASIS), and directed downward perpendicular to the skin surface until two distinct "pops" are felt, corresponding to the external and internal oblique fascial layers. The entire volume of local anesthetic is then deposited in this plane. Success with this technique ranges from 35-75% in the literature (1-3). Studies have shown that volumes as low as 0.075 mL/kg of 0.25% levobupivacaine have provided equal analgesia to 0.2 mL/kg for up to 4 hours post-operatively when ultrasound guidance is used to ensure placement of local anesthetic near the ilio-inguinal and/or ilio-hypogastric nerves (4), resulting in a 100% success rate for this block.

We are proposing a technique that will deliver 1/3 of the total dose of local anesthetic (0.3 mL/kg of 0.25% bupivacaine) for each layer of the lower anterior abdominal wall. Due to the anatomic variability of the course of the ilio-inguinal and ilio-hypogastric nerves, we believe that the placement of 0.1 mL/kg in each of the external oblique, internal oblique, and transversus abdominis layers will improve the success of the "fascial click" approach without the need for ultrasound guidance. In addition, the ilio-inguinal nerve block has a known complication of unintended femoral nerve block. The incidence of femoral nerve block varies from 4.5% to 9% (5); in fact, one randomized controlled trial of ilio-inguinal nerve block for inguinal hernia repair in adults had to be stopped prior to completion due to patient harm (falls, etc) from femoral nerve blockade (6). We propose that a 3-layer technique will have a lower incidence of unintended femoral nerve block as compared to the conventional single-shot technique.

For inguinal surgery (orchidopexy, inguinal hernia repair, or hydrocele repair), both the ilio-inguinal and ilio-hypogastric nerves need to be blocked. The ilio-inguinal nerve arises from L1 and follows the inguinal canal to innervate the medial aspect of the thigh, anterior scrotum or labia. The ilio-hypogastric nerve has an anterior cutaneous branch the runs at the level of the ASIS, providing innervation to the skin and subcutaneous tissues of the inguinal region. For orchidopexy surgery, additional local anesthetic may be needed if the scrotal incision is towards the apex of the scrotum (posterior - perineal nerve vs anterolateral - genito-femoral nerve) rather than on the anterior aspect.

Study Goals and Objectives Primary Objective - To introduce a new technique of IHN/IIN blocks that is equianalgesic to the single-shot technique without requiring ultrasound guidance.

Secondary Objective - To introduce a technique that has a lower incidence of unintended femoral nerve block.