This prospective observational study aims to evaluate the relationship between ultrasound-derived rectus abdominis muscle thickness and thickening fraction and postoperative opioid consumption in geriatric patients undergoing abdominal surgery. Preoperative ultrasonographic measurements will be performed during routine clinical care, and postoperative pain scores and analgesic requirements will be recorded within the first 24 hours. The findings may help improve individualized analgesic strategies by identifying patient-specific predictors of postoperative opioid needs.

Inclusion Criteria:

• Age ≥65 years
• Scheduled for elective midline abdominal surgery
• ASA physical status I-III
• Planned to receive bilateral ultrasound-guided rectus sheath block as part of routine clinical practice
• Provided written informed consent

Exclusion Criteria:

• Known allergy or hypersensitivity to local anesthetics
• Infection or skin lesion at the injection site
• Systemic infection or sepsis
• Coagulopathy (INR >1.5 or platelet count <100,000/mm³)
• Use of therapeutic anticoagulation not safely managed perioperatively
• History of previous midline laparotomy
• History of abdominal mesh implantation or abdominal wall reconstruction
• Significant abdominal wall pathology (e.g., large hernia) affecting anatomy
• Neuromuscular disease (e.g., myasthenia gravis, ALS, muscular dystrophy)
• Inability to perform required maneuver for dynamic ultrasound measurement
• Moderate to severe cognitive impairment or poor cooperation
• Body mass index (BMI) >40 kg/m²
• Cachexia or severe malnutrition
• Chronic opioid use (≥3 months)
• Chronic pain syndromes requiring regular analgesic use
• Alcohol or substance abuse
• Emergency surgery
• Use of additional regional anesthesia techniques (e.g., epidural, TAP block)
• Inadequate ultrasound visualization of the target anatomical plane

The study population will consist of geriatric patients (≥65 years) scheduled for elective midline abdominal surgery at S.B.U. Haseki Training and Research Hospital. All participants will receive bilateral ultrasound-guided rectus sheath block as part of routine clinical practice under general anesthesia. Eligible patients who meet the inclusion criteria and provide written informed consent will be prospectively enrolled.