Impact of High Versus Lower Oxygen Fraction Prior to Extubation on Postoperative Pulmonary Atelectasis Measured With EIT

Study Summary

Patients undergoing general anesthesia require mechanical ventilation (artificial delivery of air and oxygen to their lungs). It is well known that during mechanical ventilation, so-called atelectasis formation occurs. This is a condition characterized by partial or complete collapse of lung tissue that can result in a reduction in oxygen uptake through the lung. A known risk factor for atelectasis formation during mechanical ventilation is the utilization of high oxygen concentration, as the oxygen molecules are absorbed in the lung, which then can lead to collapse of the tissue. Despite the proven association, standard operating procedure at the end of anesthesia still requires utilization of 100% oxygen. Its justification is the goal to ensure sufficient oxygenation throughout the extubation phase. However, clinical observation doesn't show a lack of oxygenation in this phase, but the patient is still exposed to the risk of atelectasis formation. This study aims to investigate the hypothesis of whether the utilization of reduced inspiratory oxygen concentration before extubation (70% or 40% compared to 100%) reduces atelectasis formation. The study was originally planned to randomize 24 patients to either 70% or 100% inspiratory oxygen concentration at the end of anaesthesia. After completion of this first phase, the study was amended to enroll another 24 patients randomized to 40% or 100% inspiratory oxygen concentration at the end of anaesthesia. Of note, both concentrations are still higher than when breathing room air in, which has of 21% oxygen. During the intervention, parameters such as the oxygen content in the blood (oxygen saturation, SpO₂), heart rate, and blood pressure are recorded, and atelectasis formation is measured using a technique called electrical impedance tomography (EIT). EIT measurements are performed at designated time points during the procedure. Anesthesia care providers are asked to document procedural, patient, and ventilator data

Primary Outcome

The Center of Ventilation (CoV) is a variable based on the EIT. It is calculated after the initial measurements and defines the most ventilated area of the lung. Assumptions on atelectasis formation can be drawn when the CoV shifts to more ventral areas than measured before. Primary outcome is the absolute difference between the first measurement (before induction) and the measurement directly after extubation in %.

Interventions

• PROCEDURE Ventilating the patient with lower (40 or 70%) oxygen concentration during the wash out phase, before extubation