Unilateral Ventilation on Cardiopulmonary Bypass During Cardiac Surgery

Lung aeration score of both lungs.

The aeration score of each lung is the sum of the aeration scores determined in each of six lung quadrants in each lung, which can range from 0 (normal ventilation) to 3 (atelectasis/consolidation).

Radiologic assessment of Kerley B lines as indicators of lung edema.

Number of Kerley B lines in both lungs determined by chest x-ray where stage 1 (no Kerley B lines) reflects best outcome, stage 2 (Kerley B lines become visible) indicates interstitial edema, and stage 3 (increased number of Kerley B lines also in non-dependent areas and partially obscured in dependent parts of the lung) are a sign of alveolar edema.

Presence of pleural effusion in chest x-ray.

Severity assessment will be semi-quantitative with 0 = no effusion, 1 = small effusion (with blunting of the basal lung segments and the costophrenic angle), 2 = moderate effusion (fluid extents to the mid-hemithorax creating a "meniscus sign"), and 3 = massive effusion (the whole lung appears opaque with displacement of the heart to the contralateral side if located unilaterally).

Determination of the Global Inhomogeneity (GI) index in both lungs separately by thoracic Electrical Impedance Tomography (EIT).

Global inhomogeneity is calculated as the sum of the absolute differences between the median value of tidal variation and every single pixel value, divided by the sum of all impedance values, to normalize the calculated values. A GI index closer to 0 represents highly homogeneous (even) ventilation. Higher values (i.e., \> 0.5) indicate that some parts of the lung are over-distended while others are poorly aerated or collapsed (atelectasis).

Worst oxygenation (Horowitz) index measured per day during routine blood gas checks.

The Horowitz index (HI) is calculated by diving arterial oxygen partial pressure determined in the blood gas by the fraction of inspired oxygen. It will be assessed after each blood gas check and the lowest HI during one day will be entered for further statistical analysis. The degree of impaired lung function will be determined as follows: HI \> 300 mmHg (healthy lung function), HI between 201-300 mmHg (mild lung injury), HI between 101-200 mmHg (moderately severely impaired lung function), and HI \< 100 mmHg (severe lung injury, ARDS).

Length of ICU and hospital stay.

The duration from transfer to the intensive care unit until discharge to a step-down unit and the duration of hospitalization of the patient will be determined in days.

In-hospital mortality.

It will be recorded if the patient has been discharged from the hospital alive.

Duration on respiratory support via endotracheal tube.

The hours between arrival of the intubated patient on the intensive care unit until extubation will be determined.

Postoperative complications.

Any complication that poses a risk for the patient occurring during the hospital stay and having been documented in the patient's file will be retrieved by carefully reviewing the files and recorded.