Atelectasis · What Is It, Causes, Diagnosis, and More

Atelectasis is the collapse of a small or large area of lung tissue, leading to impaired gas exchange. It occurs when the alveoli—tiny air sacs at the ends of bronchioles—deflate or fail to fill with air. Alveoli are the primary site of oxygen and carbon dioxide exchange in the body and are normally lined with surfactant, a substance that prevents their collapse.  

 Atelectasis is a common postoperative complication that can also result from other conditions. If left untreated, it may become life-threatening.  

Atelectasis can be categorized as obstructive (resorptive) or nonobstructive, based on the underlying mechanism. Obstructive atelectasis occurs when an airway is physically blocked, preventing ventilation of distal alveoli. The trapped air is gradually absorbed into the bloodstream, leading to alveolar collapse. 

Nonobstructive atelectasis includes forms that occur without a discrete airway blockage and is divided into compressive, contraction, adhesive, and passive atelectasis. Compressive atelectasis results from external pressure on the lung parenchyma, limiting expansion. Contraction atelectasis is caused by scar tissue or fibrosis interfering with alveolar expansion and recoil. Adhesive atelectasis develops when surfactant is deficient or functionally impaired, increasing alveolar surface tension and promoting collapse. Passive atelectasis occurs when alveolar collapse results from hypoventilation, which leads to reduced alveolar expansion and subsequent loss of volume.  

Postoperative atelectasis is a common clinical presentation rather than a distinct mechanistic category and may involve both obstructive and nonobstructive processes, though it is most often driven by nonobstructive mechanisms related to general anesthesia.  

The causes of atelectasis vary according to type and mechanism.  

Obstructive (resorptive) atelectasis may result from airway blockage by mucus plugs, foreign bodies, tumors, or thick secretions, particularly in conditions associated with increased mucus production such as chronic obstructive pulmonary disease (COPD) or cystic fibrosis.  

Nonobstructive atelectasis can be divided into several subtypes, each with its own mechanism and cause. Compressive atelectasis may occur when external forces limit lung expansion, such as pleural effusion, pneumothorax, or upward displacement of abdominal organs into the thoracic cavity, as seen with diaphragmatic hernia. Contraction atelectasis is caused by scar tissue in individuals with chronic lung diseases like tuberculosis or sarcoidosis. Adhesive atelectasis can result from surfactant deficiency or dysfunction, as seen in neonatal and adult  respiratory distress syndromes. Passive atelectasis results from hypoventilation, which may occur in settings of impaired respiratory drive, neuromuscular weakness, or prolonged immobility.  

Postoperative atelectasis is largely related to general anesthesia, which contributes through multiple mechanisms, including loss of respiratory muscle tone, decreased functional residual capacity, airway closure, and the use of high inspired oxygen concentrations that promote absorption of alveolar gas. While surfactant dysfunction may contribute, the dominant mechanisms involve compression and absorption of gas behind closed or poorly ventilated airways, rather than isolated surfactant loss. 

Risk factors for atelectasis include underlying pulmonary or neuromuscular disease, advanced age, obesity, smoking history, and prolonged immobility. In surgical settings, the type of anesthesia, duration of surgery, and adequacy of postoperative pain control also significantly influence risk.  

Signs and symptoms of atelectasis often depend on the extent and rapidity of onset of the condition. If only a small area of the lung is affected, people may be asymptomatic. In more severe cases, people may experience shortness of breath (dyspnea), cough, or chest pain. Additionally, people may develop tachypnea (fast, shallow breathing) or tachycardia (increased heart rate).  

Due to decreased oxygen levels, some people may develop cyanosis, a bluish discoloration of the skin, particularly of the lips or fingertips. On physical examination, there may be decreased chest expansion, especially on the affected side, and reduced breath sounds over the area of atelectasis.  

Atelectasis can be challenging to diagnose because its signs and symptoms are often nonspecific, and other causes of respiratory symptoms may need to be excluded. Diagnosis begins with a thorough history and physical examination. During the physical exam, a clinician may note reduced chest wall expansion, decreased or absent breath sounds, and dullness to percussion over the affected area. Crackles (basilar crackles) may also be heard, particularly as the lung begins to re-expand. 

After the physical exam, chest imaging is typically required to confirm the diagnosis and help identify the underlying cause. A chest radiograph is most commonly used and may show areas of lung collapse, volume loss, or mediastinal shift toward the affected side. Chest radiography can also help distinguish atelectasis from pneumonia or other causes of hypoxemia. In adults, atelectasis most commonly affects the lower lobes of the lungs. In selected cases, computed tomography (CT) may be used for further evaluation, particularly when obstruction or malignancy is suspected, while ultrasound may be helpful at the bedside in people who are critically ill.  

Treatment for atelectasis depends on the underlying cause, type, and severity of the condition. Postoperative atelectasis, particularly within the first 24 hours after surgery, often resolves with conservative measures, such as deep-breathing exercises, incentive spirometry, early ambulation, and adequate pain control.  

If hypoxemia is present, supplemental oxygen may be administered via a nasal cannula or face mask. 

When atelectasis is caused by airway obstruction, such as a mucus plug, bronchoscopy may be used to directly visualize and remove the obstruction. Nebulized bronchodilators may be added in selected cases to help improve airway patency.  

If atelectasis is secondary to an underlying condition such as a tumor or chronic lung disease, treatment is directed at the primary cause, which may include surgery, radiation therapy, or chemotherapy. 

With timely and appropriate management, atelectasis is often reversible, and lung expansion can be restored with minimal long-term complications. 

Prevention of atelectasis, especially after surgery, generally involves measures that promote lung expansion. Deep-breathing exercises help keep the alveoli open and may be performed using an incentive spirometer, which encourages slow, deep inhalation and provides visual feedback on breathing effort.  

Additional postoperative prevention strategies include adequate pain control, early ambulation, frequent repositioning, and regular coughing exercises, all of which help improve ventilation and clear secretions. 

To prevent atelectasis in individuals with chronic lung diseases, such as cystic fibrosis, chest physiotherapy may be used to facilitate mucus clearance. This may include postural drainage (using gravity-assisted positioning), directed coughing, and chest percussion, in which the clinician or caregiver taps on the chest wall to help loosen and mobilize secretions.