The primary objective of this study is to evaluate and compare the efficacy of different volumes of local anesthetics, administered at the same total dose, for ilioinguinal and iliohypogastric (II/IH) nerve blocks in patients undergoing unilateral inguinal hernia repair.

The investigators aim to determine whether varying the injectate volume-while keeping the total drug amount constant-influences the quality and duration of postoperative analgesia. By monitoring pain scores and opioid consumption, this research seeks to identify the optimal volume-to-dose ratio for enhancing patient recovery and pain management following inguinal 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).

Sensory block success is confirmed via pin-prick and cold tests 20-30 minutes after the procedure. Spinal anesthesia is subsequently performed at the L3-L4 level using 15 mg of 0.5% hyperbaric bupivacaine.

Outcome Measures and Follow-up Following surgery, patients are monitored in the Post-Anesthesia Care Unit (PACU) and transferred to the ward once they meet standard discharge criteria (Bromage score ≤2, Aldrete score ≥9).

Primary Outcome: Time to first analgesic requirement, defined as the duration from the block administration until the patient reports a Visual Analog Scale (VAS) or Numerical Rating Scale (NRS) score of ≥4.

Secondary Outcomes: * Static and dynamic VAS/NRS scores at 0, 2, 6, 12, and 24 hours postoperatively.

Total 24-hour tramadol consumption (100 mg IV tramadol is administered as rescue analgesia for pain scores ≥4).

Incidence of postoperative complications (nausea, vomiting, urinary retention, hematoma, pruritus).

Time to first mobilization and patient/surgeon satisfaction.

Assessment of chronic postoperative pain at 3 and 6 months through outpatient follow-ups or telephone interviews.

Statistical Analysis Statistical analysis will be performed using SPSS version 26.0.

Descriptive data will be presented as mean, standard deviation, median, minimum, maximum, frequency, and percentage.

Normality will be assessed using skewness and kurtosis.

Between-group comparisons will be performed using independent samples t-test or Mann-Whitney U test.

Repeated measures ANOVA with Bonferroni post hoc test will be used for within-group comparisons over time.

Categorical variables will be analyzed using Chi-square test.

A p-value ≤ 0.05 will be considered statistically significant.

Inclusion Criteria:

• Patients aged between 18 and 75 years
• American Society of Anesthesiologists (ASA) physical status I, II, or III
• Diagnosis of unilateral inguinal hernia
• Scheduled for elective open inguinal hernia repair under spinal anesthesia

Exclusion Criteria:

• Age under 18 or over 75 years
• ASA physical status IV or higher
• Body mass index (BMI) greater than 35 kg/m²
• Pregnancy or suspected pregnancy
• Emergency surgery
• Refusal to provide informed consent
• Known or suspected coagulopathy
• Local infection at the site of the nerve block
• Known allergy to local anesthetics
• History of chronic opioid use or substance abuse
• Cognitive impairment or inability to cooperate with study procedures (e.g., inability to use the visual analog scale)

"Individual participant data will not be shared to protect patient confidentiality and ensure compliance with local data protection regulations. The study protocols and results will be made available through publication, but the raw data set is restricted to the primary investigators to maintain the integrity of the institutional data policy."

"A double-blind masking protocol will be implemented. The patients will be blinded to their group assignment (Participant masking). The physician performing the ultrasound-guided block will be aware of the volume administered due to the nature of the intervention. However, a separate investigator, who is blinded to the group allocations and volume administered, will perform all postoperative assessments, including pain scores (VAS) and analgesic consumption (Outcomes Assessor masking). Randomization codes will be kept in sealed, opaque envelopes and will only be opened by the performing anesthesiologist."