The Effect of Different Volumes of Ilioinguinal-Iliohypogastric Nerve Block on Postoperative Analgesia in Inguinal Hernia Surgery

Study Design and Patient Selection This study is designed as a prospective, randomized, controlled, single-center trial to evaluate the efficacy of different local anesthetic volumes in ilioinguinal-iliohypogastric (II-IH) nerve blocks. The study is conducted in accordance with the Declaration of Helsinki. Patients aged 18-75, with an ASA physical status of I-III, scheduled for unilateral open inguinal hernia repair under spinal anesthesia, are eligible for inclusion. Exclusion criteria include BMI >35 kg/m², pregnancy, emergency surgery, coagulopathy, infection at the injection site, known allergy to local anesthetics, chronic opioid use, and cognitive impairment.

Randomization and Blinding A total of 70 patients are randomly assigned to two equal groups (1:1 ratio) using a computer-generated sequence and the sealed envelope method. The study is assessor-blinded; while the anesthesiologist performing the nerve block is aware of the group allocation, the researchers responsible for postoperative pain assessment and the statisticians are blinded to the group assignments.

Interventional Procedure All patients receive standard monitoring and minimal sedation with 1 mg of IV midazolam. The II-IH nerve block is performed under ultrasound guidance (high-frequency linear probe) 30 minutes before spinal anesthesia using an in-plane technique. The needle is positioned between the internal oblique and transversus abdominis muscles, and the position is confirmed via hydrodissection.

Group 1 (Low Volume): Receives 10 mL of 0.375% bupivacaine (7.5 mL of 0.5% bupivacaine + 2.5 mL of saline).

Group 2 (High Volume): Receives 20 mL of 0.1875% bupivacaine (7.5 mL of 0.5% bupivacaine + 12.5 mL of saline).