This clinical trial aims to evaluate the effectiveness of an ultrasound-guided nerve block technique as the sole anesthetic method for patients undergoing outpatient umbilical hernia surgery. The procedure, called rectus sheath block (RSB), involves injecting local anesthetic near the abdominal muscles to reduce pain during and after surgery. The study will compare two groups of adult patients: one receiving the nerve block with a medication called clonidine added to the anesthetic solution, and the other receiving the same block without clonidine. Clonidine may help improve pain control and reduce the need for additional pain medications. By analyzing pain scores, recovery quality, and potential side effects, the study seeks to determine whether the use of clonidine in this context is safe, cost-effective, and beneficial for patient recovery. Participants will answer questionnaires about their pain and recovery during the first 48 hours after surgery.

This is a prospective, randomized, double-blind, controlled clinical trial designed to evaluate the effectiveness and safety of adding clonidine to a local anesthetic solution for ultrasound-guided rectus sheath block (RSB) in adult patients undergoing ambulatory umbilical hernioplasty. The study will be conducted at the Ambulatory Surgery Unit of the Policlínica Universitária Piquet Carneiro, part of the Universidade do Estado do Rio de Janeiro (UERJ), between January 2025 and April 2026.

Eligible patients (ASA I or II, aged 18-65) scheduled for elective outpatient umbilical hernia repair with a hernial defect ≤ 4 cm will be randomized into two groups. The intervention group (BRA-CLO) will receive bilateral RSB with a solution containing 8 mL of lidocaine 2%, 8 mL of ropivacaine 1%, and clonidine 75 mcg, diluted in 0.9% saline to a total volume of 20 mL, administered on each side. The control group (BRA) will receive an identical volume and concentration of local anesthetic without the addition of clonidine.

RSB will be performed under real-time ultrasound guidance (Butterfly iQ+ probe) using an in-plane technique with a Quincke 22G needle. Sedation with midazolam, fentanyl, and propofol will be administered as required. The block will be performed preoperatively under standard monitoring, including ECG, pulse oximetry, and non-invasive blood pressure.

The primary hypothesis is that the addition of clonidine will enhance the quality of intraoperative and postoperative analgesia, reduce opioid consumption, and improve overall postoperative recovery without increasing the risk of adverse events. To assess recovery quality, the validated Quality of Recovery-15 (QoR-15) questionnaire will be administered at postoperative 24 and 48 hours. Pain will be assessed using the Numeric Rating Scale (NRS) at predefined intervals (PACU, 24h and 48h). Sedation will be measured with the Richmond Agitation-Sedation Scale (RASS), and adverse events such as bradycardia, nausea, vomiting, conversion to general anesthesia, and postoperative complications will be recorded.

Randomization will be performed using block randomization with variable block sizes (4, 6, or 8) generated in R (v4.4.1), and allocation concealment will be ensured with sealed opaque envelopes. Data will be collected and managed using the REDCap platform, ensuring confidentiality and integrity.

The study aims to fill an important gap in evidence regarding the use of alpha-2 adrenergic agonists as adjuvants in abdominal wall blocks, especially in the context of ambulatory surgery. It is expected that the findings will support the safe and effective use of clonidine to optimize regional anesthesia protocols in hernia repair.

Inclusion Criteria:

• Adults aged 18 to 65 years;
• Both male and female participants;
• ASA physical status I or II (American Society of Anesthesiologists classification);
• Scheduled for elective ambulatory umbilical hernia repair;
• Hernial defect size ≤ 4 cm (small to medium).

Exclusion Criteria:

• Refusal or inability to provide written informed consent;
• Cognitive or psychiatric disorders that impair comprehension or adherence to the study protocol;
• Known allergy or hypersensitivity to local anesthetics, clonidine, opioids, nonsteroidal anti-inflammatory drugs (NSAIDs), or other analgesics;
• Participation in another clinical trial within the previous 30 days;
• Missing data or loss to follow-up during postoperative assessments;
• Contraindications to regional anesthesia or known coagulopathy.

Individual participant data (IPD) will be made available upon reasonable request to the corresponding author, following appropriate de-identification procedures and in accordance with local ethical guidelines.

Individual participant data (IPD) and supporting information will be made available beginning 6 months after publication of the primary results and will remain available for 5 years after publication.

Access to the de-identified individual participant data and supporting documents will be granted to qualified researchers upon reasonable request, provided that the proposed use is for scientific research purposes and complies with institutional and ethical guidelines. Requests should be submitted to the corresponding author and will be evaluated by the research team. Data will be shared under a data use agreement.