This study compares two ways of reopening collapsed parts of the lung in patients on a ventilator.

In one group, doctors use a small camera (bronchoscope) to guide air pressure directly to the blocked part of the lung. In the other group, increased air pressure is applied to the whole lung using the ventilator.

Patients are carefully monitored to ensure safety.

This study will compare two lung recruitment strategies in mechanically ventilated patients with segmental atelectasis.

In the experimental group, patients will undergo bronchoscopy-guided targeted segmental recruitment using endobronchial bloker. A flexible bronchoscope will be introduced through the endotracheal tube and advanced under direct visualization to the affected lung segment. The endobronchial blocker will be positioned to temporarily block the segmental bronchus, creating a closed system. Sustained positive pressure of 30 cmH₂O will be applied directly to the atelectatic segment for 30 minutes, while standard ventilator settings will be maintained for the remainder of the lung. Continuous monitoring of oxygen saturation, heart rate, blood pressure, and end-tidal carbon dioxide will be maintained. The maneuver will be immediately discontinued if oxygen saturation decreases by more than 10%, systolic blood pressure decreases by more than 20%, or heart rate changes by more than 20% from baseline values.

In the control group, patients will receive a conventional whole-lung recruitment maneuver. Continuous positive airway pressure (CPAP) of 40 cmH₂O will be applied to the entire respiratory system for 40 seconds using the ventilator. Monitoring and safety criteria will be identical to those used in the experimental group, and the maneuver will be discontinued if predefined thresholds are exceeded.

All patients will receive lung-protective mechanical ventilation according to current guidelines. Tidal volumes will be maintained at 6-8 mL/kg predicted body weight, plateau pressures will be limited to less than 30 cmH₂O, and positive end-expiratory pressure (PEEP) will be adjusted according to FiO₂-PEEP tables. Permissive hypercapnia will be accepted provided arterial pH remains above 7.20.

The primary outcomes will focus on safety and will include the incidence of clinically significant desaturation (oxygen saturation decrease greater than 5% from baseline) and hemodynamic instability (systolic blood pressure decrease greater than 20 mmHg or need for vasopressor dose escalation) during and within 30 minutes after the maneuver.

Secondary outcomes will include changes in respiratory parameters measured at baseline, 24 hours, and 48 hours after the intervention. These parameters will include the PaO₂/FiO₂ ratio, static respiratory system compliance, driving pressure, plateau pressure, and PEEP. Arterial blood gas analysis will be performed at baseline, 1 hour, 24 hours, and 48 hours to assess pH, PaO₂, PaCO₂, bicarbonate, and base excess.

Clinical outcomes will include duration of mechanical ventilation following the maneuver, length of stay in the intensive care unit, duration of ward treatment after ICU discharge, in-hospital mortality, and 28-day all-cause mortality.

All patients will undergo contrast-enhanced chest computed tomography. Lung parenchyma will be segmented using 3D Slicer software to quantify total lung volume and non-ventilated (pathologic) lung regions. The proportion of non-ventilated lung tissue relative to total lung volume will be calculated. A change greater than 15% in the proportion of non-ventilated lung between baseline and follow-up scans will be considered clinically significant.

Venous blood samples will be collected at baseline, 24 hours, and 48 hours. Serum concentrations of interleukin-2 and interleukin-8 will be measured using ELISA assays. Samples will be analyzed in duplicate, and assay variability will be less than 10%.

Inclusion Criteria:

• treatment in ICU, presence of radiologically or clinically confirmed pulmonary atelectasis during ICU treatment, requirement for mechanical ventilation

Exclusion Criteria:

• primary or secondary lung malignancy