Predictive Factors for the Effectiveness of the Ilioinguinal Iliohypogastric Nerve Block for Hernia Surgery

Inguinal hernioplasty is one of the most commonly performed surgical procedures in day surgery. The need to discharge the surgical patient on the same day affects the choice of anesthetic strategy and leads to opt for those techniques that allow for faster recovery. One option is represented by the ilioinguinal (II)-iliohypogastric (IH) nerve block, a variant of the transversus abdominis plane (TAP) block, which has a safety profile, ease of execution, effectiveness in controlling intra- and post-operative pain, with a reduction in opioid administration and increased patient satisfaction. It also has additional advantages, such as rapid patient discharge, early refeeding, no need for post-anesthesia care unit (PACU) or recovery room admission.

It is not yet established what the success rate of the anesthetic block is, intended as the absence of the need for further infiltration by the surgeon, the administration of opioid drugs, or the need to convert to general anesthesia, nor what the independent risk factors are for the positive outcome of the procedure. The aim of this study is therefore to evaluate the success of the ilioinguinal-iliohypogastric block as the anesthetic strategy of choice in patients undergoing unilateral inguinal hernioplasty with the Lichtenstein technique, and the independent variables of block effectiveness, analyzing various parameters such as BMI, age, optimal ultrasound visualization, volume of anesthetic used, dose of anesthetic administered, time elapsed between the execution of the II-IH block and the incision, and the necessary dose of sedative drugs.

All patients who need to undergo unilateral inguinal hernioplasty according to the Lichtenstein technique, aged ≥ 18 years, American Society of Anesthesiology-Physical Status (ASA-PS) I-II-III, and who give their informed consent to participate in the study will be recruited. Patients with allergies to local anesthetics; heart disease, kidney disease, liver disease, uncompensated central or peripheral neuropathy; history of coagulopathy (risk/benefit ratio to be evaluated); infection at the site of the procedure; obesity (high BMI) or difficulty in visualizing target structures will be excluded. Non-cooperative patients or those taking anticoagulant therapy will also not be included.

This observational, prospective, monocentric study will be conducted in the operating rooms of the Sant'Antonio Hospital (Hospital-University Company of Padova) and will last for one year. An attempt will be made to recruit the largest number of patients within this time frame, and considering the surgical activity at the operating facility, it is estimated that approximately 400 patients will be enrolled.

The patient will be recruited after verifying the inclusion/exclusion criteria. Each patient will be informed about the study and asked for written informed consent for the treatment of personal data at the time of the standard preoperative anesthesiology visit.

The intraoperative management of the patient will be at the discretion of the anesthesiologist in charge of the patient, without making any changes to their conduct.

The patient will be monitored in the preoperative room with electrocardiogram, pulse oximetry, and non-invasive blood pressure. Once the patient is positioned on the operating table, after adequate sedation with Propofol Targeted Controlled Infusion, the locoregional anesthesia, or II-IH nerve block, will be performed using a sterile technique and under ultrasound guidance. At the end of the procedure, Paracetamol 1 g will be administered.

With this study, the commonly used anesthetic procedures are not modified, and therefore participation in this study does not entail any additional risk for the patient and there are no direct benefits associated with it. All the clinical activities foreseen for the study are classified as routine procedures as they would be performed or prescribed to the patient even in the event of refusal to participate in the study.

The project's data collection form (CRF) will be paper-based and few variables are expected to be collected. Following the longitudinal design of the study, the CRF will collect data on patients at the time of the anesthesiology visit, during the execution of the II-IH nerve block, and during the surgical procedure. The collected data will be entered into an Excel file by the experimenter and will be processed for the exclusive purposes related to the completion of this study, made anonymous, and, in this form, aggregated in the project's database, solely for the purpose of carrying out the study itself and achieving the predefined objectives. The data will not be disseminated unless in strictly anonymous and aggregated form.

All statistical analyzes will be performed using R version 3.4.0 (2017-04-21). Results will be considered statistically significant for P values ≤ 0.05.

The study data will be made public even in the case of negative results and will be sent in copy to the ethics committee within twelve months from the conclusion of data collection.