The goal of this observational study is to learn about the effectiveness of the Deep Rectus Sheath (Preperitoneal) block in patients undergoing abdominal surgery. The main question it aims to answer is:

Does the Deep Rectus Sheath block improve postoperative recovery and pain control compared to standard care or other fascial plane blocks in patients undergoing abdominal surgery?

Participants undergoing open or laparoscopic abdominal surgery as part of their routine clinical care will receive analgesic management according to standard practice, which may include systemic analgesia alone, Deep Rectus Sheath block, or other fascial plane blocks (such as TAP, ESP, or QL), depending on anesthesiologist choice. Postoperative outcomes will be collected prospectively, including quality of recovery (QoR-15 at 24 hours), pain scores at rest and during movement up to 48 hours, analgesic consumption, time to first analgesic request, mobilization time, and occurrence of complications.

This prospective, observational, non-interventional clinical study aims to evaluate postoperative recovery and analgesic outcomes in adult patients undergoing abdominal surgery (open or laparoscopic) who receive different perioperative analgesic strategies as part of routine clinical care.

The study focuses on the Deep Rectus Sheath (DRS) block, also referred to as the preperitoneal block, a recently described ultrasound-guided technique involving injection of local anesthetic beneath the posterior rectus sheath into the preperitoneal space. This approach is hypothesized to provide broader analgesia compared with the conventional rectus sheath block by targeting not only somatic afferents of the anterior abdominal wall but also the richly innervated parietal peritoneum, potentially contributing to improved control of both somatic and visceral components of postoperative pain.

Patients will not be randomized. Instead, they will be managed according to standard clinical practice and subsequently categorized based on the analgesic strategy received: (A) standard systemic analgesia alone; (B) DRS block combined with standard care; or (C) alternative or additional fascial plane blocks (such as transversus abdominis plane [TAP], erector spinae plane [ESP], or quadratus lumborum [QL] blocks) combined with standard care. Detailed data will be recorded on the type of block performed, timing (pre-incision or postoperative), technique, local anesthetic dose and concentration, and use of adjuvants.

All patients will receive multimodal postoperative analgesia according to institutional protocols, typically including scheduled non-opioid analgesics with opioids reserved for rescue therapy. The study does not alter clinical management.

The primary outcome is postoperative quality of recovery, assessed using the Quality of Recovery-15 (QoR-15) score at 24 hours after surgery. Secondary outcomes include postoperative pain scores at rest and during movement at predefined time points up to 48 hours, patient satisfaction (Likert scale), total analgesic consumption, time to first rescue analgesic request (duration of analgesia), time to first mobilization, incidence of postoperative nausea and vomiting, use of antiemetics, and occurrence of complications.

Safety assessment will include monitoring for block-related complications during and immediately after the procedure (e.g., vascular puncture, paresthesia, pain, local anesthetic systemic toxicity), early postoperative complications, and delayed adverse events, including neurological symptoms evaluated up to 7 days after surgery.

The study is exploratory in nature, with sample size based on feasibility, and is expected to be completed within 12 months. Statistical analysis will include comparisons of baseline characteristics and outcomes between groups using appropriate parametric or non-parametric tests, as well as linear mixed-effects models for repeated measures over time. A p-value <0.05 will be considered statistically significant.

Inclusion Criteria:

• Age ≥ 18 years
• Patients undergoing abdominal surgery, either open or laparoscopic
• ASA physical status I-III
• Neuraxial or general anesthesia according to standard clinical practice
• Provision of informed consent to participate in the study

Exclusion Criteria:

• Refusal to provide informed consent
• Contraindications to locoregional anesthesia
• Known allergy to local anesthetic agents
• Coagulation disorders or incompatible anticoagulant therapy
• Infection at the injection site
• Cognitive impairment preventing reliable assessment of outcomes

Patients undergoing abdominal surgery, either open or laparoscopic