This prospective observational study aims to evaluate the association between postoperative oxygenation, assessed by the SpO₂/FiO₂ ratio, and body mass index (BMI), STOP-BANG score, and postoperative analgesic methods in patients undergoing elective laparoscopic cholecystectomy in the reverse Trendelenburg position. Postoperative SpO₂ and FiO₂ values will be recorded within the first postoperative hour, and the SpO₂/FiO₂ ratio will be calculated. Analgesic techniques applied as part of routine clinical practice will be documented. The study does not involve any additional intervention beyond standard care. The findings are expected to contribute to a better understanding of factors associated with early postoperative oxygenation and hypoxemia risk.

Inclusion Criteria:

• Age ≥ 18 years
• Patients who provide written informed consent
• ASA physical status I-III
• Patients undergoing elective laparoscopic cholecystectomy
• Surgery performed in the reverse Trendelenburg position (30°)
• Expected operative duration < 3 hours
• Exclusion Criteria:
• Age < 18 years
• Refusal or inability to provide informed consent
• ASA physical status IV or higher
• Known chronic respiratory diseases (e.g., asthma, COPD)
• Severe cardiac failure (NYHA class III-IV) or advanced cardiovascular disease
• Emergency surgery
• Preoperative oxygen supplementation or baseline SpO₂ < 90%
• Prolonged intubation or perioperative respiratory complications
• Requirement for postoperative noninvasive ventilation or intensive care unit admission
• Missing SpO₂ or FiO₂ data preventing calculation of the SpO₂/FiO₂ ratio

The study population consists of adult patients aged 18 years and older with ASA physical status I-III who undergo elective laparoscopic cholecystectomy in the reverse Trendelenburg position. All participants provide written informed consent. Patients with significant respiratory or cardiovascular comorbidities, emergency surgery, or perioperative respiratory complications are excluded.