One-lung ventilation is commonly used during thoracic surgery but is frequently associated with impaired oxygenation and altered respiratory mechanics. Traditional oxygenation indices require arterial blood gas analysis and do not fully reflect the mechanical stress applied to the lungs.

This prospective observational study aims to evaluate the correlation between oxygenation indices and oxygen saturation indices during one-lung ventilation in adult patients undergoing elective thoracic surgery. Modified indices incorporating driving pressure and mechanical power will also be assessed.

No intervention beyond standard clinical care will be applied. The findings of this study may help clarify the clinical utility of non-invasive oxygenation indices for intraoperative monitoring during one-lung ventilation.

One-lung ventilation induces complex changes in pulmonary physiology, including increased intrapulmonary shunt and altered respiratory mechanics, which may challenge conventional approaches to intraoperative oxygenation assessment. While invasive oxygenation indices are widely used, their applicability during one-lung ventilation is limited by the need for arterial blood gas sampling and the lack of integration of mechanical ventilation-related stress.

Non-invasive oxygen saturation-based indices have been proposed as alternatives; however, data regarding their performance under the dynamic physiological conditions of one-lung ventilation remain scarce. Furthermore, emerging concepts in lung-protective ventilation emphasize the importance of driving pressure and mechanical power as determinants of ventilator-induced lung injury, yet these parameters are not incorporated into traditional oxygenation metrics.

In this prospective observational study, invasive and non-invasive oxygenation indices, including modified forms incorporating driving pressure and mechanical power, will be recorded simultaneously during one-lung ventilation in adult patients undergoing elective thoracic surgery. The relationships and agreement between these indices will be analyzed to assess their comparability across different levels of mechanical respiratory load.

No intervention beyond standard clinical care will be applied. Ventilatory settings and perioperative management will be determined solely by routine clinical practice. This study is designed to provide methodological insight into the intraoperative applicability of non-invasive oxygenation indices during one-lung ventilation.

Inclusion Criteria:

• Patients aged 18 years and older
• Patients classified as ASA physical status I-III
• Patients scheduled for elective thoracic surgery requiring one-lung ventilation for at least 1 hour intraoperatively
• Patients in whom simultaneous arterial blood gas analysis and continuous SpO₂ monitoring can be performed
• Patients who have provided written informed consent

Exclusion Criteria:

• Patients undergoing emergency surgery
• Patients younger than 18 years of age
• Patients classified as ASA physical status IV or higher
• Patients with a history of previous thoracic surgery
• Patients with a body mass index (BMI) >40 kg/m² or <18 kg/m²
• Patients with advanced chronic lung disease (COPD stage III-IV)
• Patients with New York Heart Association (NYHA) class III-IV heart failure
• Patients undergoing surgery due to pleural effusion

Adult patients aged 18 years and older with ASA physical status I-III who are scheduled for elective thoracic surgery requiring intraoperative one-lung ventilation for at least one hour. All participants undergo standard perioperative management with simultaneous arterial blood gas analysis and continuous pulse oximetry monitoring during surgery.