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

This study is a single blinded randomized controlled trial with two study arms ("intervention" and "control") and aims to assess whether the use of 100% oxygen before extubation favors postoperative atelectasis formation compared to the use of 70% oxygen concentration whilst still ensuring patient safety.

The randomization scheme is developed by a non-blinded statistician using the Statistical Analysis Software (SAS) and uploaded to the Research Electronic Data Capture (REDCap) randomization module, enabling delegated team members to generate sequential allocations for enrolled subjects.

Screening of potential study subjects is performed by the PI. The patient is asked to participate in the study by the PI or co-investigator and the study design and procedures are explained to the patient, while they are still in the holding area on the day of the procedure.

The patients in both groups (intervention and control) are equipped with the EIT belt as well as an additional SpO2 recording device before induction and intubation. After onset of mechanical ventilation as to institutional standards, an inspiratory oxygen concentration of 50% is aimed. Actual oxygen concentration as well as any administration of drugs remain at the discretion of the anesthesia care provider. At the end of the procedure, before the initiation of volatile anesthetic washout, fresh gas flow is increased to 15 liters per minute (or the highest fresh gas flow allowed at the respective anesthesia machine if 15 liters per minute cannot be achieved), and a fraction of inspired oxygen (FiO2) of either 70% (intervention group) or 100% (control group) is applied.

EIT measurements take place at 6 designated time points before, during and after the procedure. These time points are: Pre-induction, after intubation, just before washout, pre-extubation, one minute after extubation and 60 minutes after extubation in the PACU.

The primary outcome for the study is the Center of Ventilation (CoV), measured through electrical impedance tomography (EIT) compared at one minute after extubation between the two groups.

Secondary outcomes include the homogeneity index, and the distribution of lung aeration measured by EIT. In addition, we measure the peripheral oxygen concentration during the whole interventional period and during the PACU stay to evaluate any occurrence of desaturation (SpO2 <90%) within the first 60 minutes after extubation in the PACU. The incidence of re-intubation or the need for non-invasive ventilation in the next 7 days and an unplanned admission, to either ICU, Intermediate Care Unit (IMC) or the normal ward, as well as the length of stay in the PACU are other clinical secondary outcomes compared between the two groups.