atelectasis

Atelectasis is the partial or complete collapse of a portion of the lung or of an entire lung, resulting from incomplete expansion or loss of air from the air spaces. It reduces the surface area available for gas exchange and can cause low oxygen levels and respiratory distress depending on the extent.

Atelectasis can arise from several mechanisms. Obstructive (absorption) atelectasis occurs when an airway is blocked by mucus, a foreign body, or a mass, allowing the air within the alveoli to be absorbed and the alveolar walls to collapse. Compression atelectasis happens when external pressure—such as from a pleural effusion, pneumothorax, or chest wall restriction—compresses a part of the lung. Contraction or fibrotic atelectasis results from scarring or fibrosis that prevents normal expansion. In newborns and preterm infants, surfactant deficiency can contribute to atelectasis, while postoperative and critically ill patients are at higher risk due to shallow breathing, pain, or sedation.

Clinical features vary with severity and location. Common signs include dyspnea, tachypnea, diminished or absent breath sounds over the affected area, and dullness to percussion. Hypoxemia may occur, and radiographic findings show increased density with volume loss and possible displacement of fissures or mediastinal structures.

Diagnosis is usually made with chest radiography, which identifies lobar collapse or segmental opacification. Ultrasound and computed tomography can help delineate surrounding structures and underlying causes. Evaluation should address the underlying cause, such as relieving airway obstruction or treating a pleural effusion.

Management focuses on treating the cause and re-expanding the collapsed lung. Measures include airway clearance techniques, incentive spirometry, deep-breathing exercises, adequate analgesia, early mobilization after surgery, and bronchoscopy or suctioning if a blockage is present. Prognosis is generally favorable with prompt treatment, though persistent atelectasis raises risk for infection and complications.