This study aims to compare standard positive end-expiratory pressure (PEEP) with dynamic compliance-guided individualized PEEP in obese patients undergoing elective spinal surgery under general anesthesia. Obesity and prone positioning during spinal surgery are associated with reduced lung compliance, atelectasis, and an increased risk of postoperative pulmonary complications.

Participants will be allocated to receive either a fixed standard PEEP or an individualized PEEP level determined according to intraoperative dynamic lung compliance. Intraoperative oxygenation, respiratory mechanics, arterial blood gas parameters, and hemodynamic variables will be assessed at predefined time points. Postoperative pulmonary complications within the first 24 hours after surgery will also be evaluated.

The study seeks to determine whether individualized PEEP titration based on dynamic compliance offers physiological or clinical advantages compared with a standard PEEP strategy in this patient population.

Inclusion Criteria:

• Adult patients aged 18-65 years
• Body mass index (BMI) ≥30 kg/m²
• Scheduled for elective spinal surgery under general anesthesia
• Requirement for intraoperative mechanical ventilation
• American Society of Anesthesiologists (ASA) physical status II-III
• Provision of written informed consent

Exclusion Criteria:

• Pre-existing severe pulmonary disease (e.g., COPD GOLD stage III-IV, restrictive lung disease)
• Severe cardiac disease (e.g., heart failure with reduced ejection fraction, significant valvular disease)
• History of thoracic surgery affecting lung mechanics
• Pregnancy
• Emergency surgery
• Intraoperative need for deviation from the planned ventilation protocol