This randomized controlled clinical trial aims to compare the effects of two different positive end-expiratory pressure (PEEP) levels (5 cmH₂O and 8 cmH₂O) on respiratory mechanics in patients undergoing lumbar spine surgery in the prone position under total intravenous anesthesia (TIVA). Prone positioning may adversely affect lung compliance and gas exchange, making optimal ventilatory strategies essential. Driving pressure and mechanical power are considered key determinants of ventilator-induced lung stress. This study will evaluate the impact of different PEEP levels on respiratory parameters and intraoperative physiological changes.

Prone positioning during lumbar spine surgery is associated with increased intrathoracic pressure, reduced lung compliance, and impaired ventilation-perfusion matching, which may negatively affect respiratory mechanics and gas exchange. Mechanical ventilation strategies, particularly the application of positive end-expiratory pressure (PEEP), play a critical role in preventing atelectasis and optimizing oxygenation.

Pressure-controlled ventilation with volume guarantee (PCV-VG) is a modern ventilation mode that ensures target tidal volume delivery while minimizing airway pressures, thereby reducing the risk of ventilator-induced lung injury. In recent years, driving pressure (ΔP) and mechanical power have emerged as important parameters reflecting lung stress and injury during mechanical ventilation.

This prospective randomized controlled trial aims to evaluate the effects of two different PEEP levels (5 cmH₂O and 8 cmH₂O) on respiratory mechanics and gas exchange in patients undergoing lumbar spine surgery in the prone position under total intravenous anesthesia (TIVA). Patients will be randomly assigned into two groups receiving either 5 cmH₂O or 8 cmH₂O PEEP. Ventilation will be standardized using PCV-VG mode with a tidal volume of 6-8 mL/kg predicted body weight and respiratory rate adjusted to maintain normocapnia.

Hemodynamic parameters and respiratory variables, including peak airway pressure, plateau pressure, dynamic compliance, airway resistance, tidal volume, and end-tidal CO₂, will be recorded at predefined time points. Arterial blood gas analyses will be performed at selected intervals to assess gas exchange.

The primary outcome of the study is driving pressure (ΔP), while secondary outcomes include mechanical power, oxygenation parameters, PaCO₂-EtCO₂ gradient, and physiologic dead space fraction (VD/VT).

The findings of this study are expected to provide clinical evidence regarding the optimal PEEP level in prone lumbar surgery and contribute to improving intraoperative lung-protective ventilation strategies.

Inclusion Criteria:

• Patients aged between 18 and 65 years
• American Society of Anesthesiologists (ASA) physical status I-II
• Scheduled for elective lumbar spine surgery in the prone position
• Planned general anesthesia with total intravenous anesthesia (TIVA)
• Ability to provide informed consent

Exclusion Criteria:

• Body mass index (BMI) ≥ 30 kg/m²
• History of significant pulmonary disease (e.g., COPD, asthma)
• Severe cardiovascular disease
• Pregnancy
• Known difficult airway
• Requirement for intraoperative vasopressor infusion due to hemodynamic instability
• Conversion to different surgical position or change in surgical plan
• Incomplete data or protocol deviation

This is an open-label study. Due to the nature of the intervention (ventilator settings), masking of care providers and investigators is not feasible.