Comparing Ilioinguinal Single-shot and Three-layer Blocks

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.

Study Design Randomized controlled trial comparing two groups: single-shot group (0.3 mL/kg of 0.25% bupivacaine placed 1 cm medial to the ASIS following two "pops" via the fascial click method), and the three-shot (TS) group, where 1/3 of the total dose above is deposited in each of the 3 layers (external and internal oblique, transversus abdominis). In the TS group, 0.1 mL/kg of 0.25% bupivacaine will be injected per layer.

Methods After IRB approval, ASA I-II children presenting for inguinal surgery (orchidopexy, inguinal hernia, or hydrocele repair) whose parents have already given consent for an ilio-inguinal nerve block, will be approached to participate in this study. Written informed consent will be obtained from parents, while verbal assent will be obtained from children where appropriate. Exclusion criteria include patient or parental refusal, local anesthetic allergy, or contraindication to ilio-inguinal nerve block.

The ilio-inguinal nerve blocks will be performed by the attending anesthesiologist who is responsible for the child's anesthetic. Each child will be premedicated with 20 mg/kg of oral acetaminophen. Induction of anesthesia will be intravenous (propofol and remifentanil) or via facemask (oxygen and sevoflurane) according to the discretion of the attending anesthetist. Following placement of intravenous access and laryngeal mask airway, anesthesia will be maintained with 1 MAC (minimum alveolar concentration) of sevoflurane in air/O2 with spontaneous ventilation. Intraoperative monitoring will include heart rate, electrocardiogram, oxygen saturation, non-invasive arterial blood pressure, and end-tidal carbon dioxide, oxygen concentration, and anesthetic agent.

A SonoSite ultrasound unit (SonoSite M-Turbo, Bothell, WA, USA) and a SLAx 13-6 MHz linear hockey stick probe will be used to document the placement of the local anesthetic and the relevant anatomical structures. The study investigators will turn the screen away from the attending anesthesiologist performing the block and will save 'before' and 'after' images of the block onto a USB stick via the ultrasound machine. The attending anesthesiologist will sterilize the area with chlorhexidine solution and locate the ASIS. Using a blunted 20 gauge needle, they will place the needle approximately one finger's-breadth medial to the ASIS and insert perpendicular to the skin until 2 pops are felt. If the patient has been randomized to the single-shot group, following negative aspiration, all of the local anesthetic (0.3 mL/kg of 0.25% bupivacaine) will be injected here. A screen shot of local anesthetic spread will then be saved through the ultrasound machine onto a USB stick. If the patient has been randomized to the three-shot (TS) group, following negative aspiration, one third of the local anesthetic (0.1 mL/kg of 0.25% bupivacaine) will be injected here, then pulled back one "pop" to the next layer where another third of the local anesthetic will be injected. The final third of the local anesthetic dose will be injected subcutaneously in a skin wheal medial to the ASIS. Again, a screen shot of local anesthetic spread will be saved via the ultrasound machine to a USB stick. The USB stick will be password-protected using only consecutive numbers to identify the patients. The investigator who will later review the screen shots from the ultrasound will thus be blinded from patient allocation.

Following block placement, the surgeon may prep and drape the patient in preparation for the surgical procedure. Baseline heart rate and arterial blood pressure will be noted following skin incision. An increase in heart rate or arterial blood pressure greater than 20% from baseline will be treated with rescue analgesia (fentanyl 1 mcg/kg IV). For orchidopexy, additional local anesthetic (0.1 mL/kg 0.25% bupivacaine) will be used for local infiltration of the scrotal incision.

Post-operatively, analgesia will be recorded by trained pediatric nurses in the post-anesthetic care unit (PACU) using the FLACC pain scale for young children or non-verbal patients, and using the Wong-Baker Faces Pain Score for older children. Both are rated on a scale of 0-10. Any score greater than 6 will be treated with morphine 0.05 mg/kg IV, up to 2 doses, 15 minutes apart. PACU nurses will also note any quadriceps weakness, indicating an unintended femoral nerve block. Following discharge from PACU, the patients will continue to be monitored for pain scores in day surgery area for up to 4 hours post-operatively. No follow-up is planned beyond discharge from day surgery.

Studies have shown that a blind, single shot technique for ilio-inguinal nerve blocks has a success rate of 35-75% (1-3). For the purposes of our study, we will use a value of 60% efficacy for the single-shot technique. We hypothesize that a 3-shot technique will have an efficacy of 90%, based on studies showing 100% efficacy for single-shot ultrasound-guided technique (4), and 94% efficacy in a similar study (7). For a power of 0.8, alpha 0.05, we calculate a sample size of 32 patients per group.