One-lung ventilation is a mechanical ventilation method frequently used during several thoracic surgeries. One-lung ventilation requires the use of protective ventilation to limit ventilator-induced injury and reduce postoperative respiratory complications. Protective ventilation during one-lung ventilation is specific since tidal volumes are applied by definition to one lung, and it is recommended to use lower tidal volumes, down to 4 ml/kg of ideal body weight. This approach requires individualized ventilation parameters, which differs from the conventional or two-lung ventilation, and there are no clear recommendations regarding respiratory rate adjustment to ensure adequate gas exchange.

The aim of the study is to:

1. Evaluate whether the initial ventilation settings (tidal volume and respiratory rate) during one-lung ventilation are appropriate to prevent respiratory acidosis.
2. Compare the ventilation settings (tidal volume and respiratory rate) made by clinicians with those proposed by an smartphone application ''VentilO''.

Inclusion Criteria:

• Adults (≥ 18 years old)
• Patients intubated and undergoing one-lung ventilation during thoracic surgery
• Volume-controlled ventilation mode used intraoperatively

Exclusion Criteria:

• Arterial blood gas data unavailable during one-lung ventilation
• Missing demographic data (sex, height, actual weight)

Patient undergoing thoracic surgery requiring intraoperative one-lung ventilation