Atelectasis is a condition in which all or part of a lung becomes airless and collapses.
The main function of the lungs is to absorb oxygen into the bloodstream from the atmosphere and to expel carbon dioxide from the blood into the exhaled breath (gas exchange—see Biology of the Lungs and Airways: Gas Exchange Between Alveolar Spaces and Capillaries). For gas exchange to occur, the small air sacs within the lungs (alveoli) must remain open and filled with air. Alveoli are kept open by the elastic structure of the lung and by a liquid lining called surfactant. Surfactant counters the natural tendency of the alveoli to close (collapse). Periodic deep breaths, which people take unconsciously, and cough also help keep alveoli open. Cough expels any mucus or other secretions that could block the airways leading to the alveoli. If the alveoli are closed for any reason, they cannot participate in gas exchange. The more alveoli that are closed, the less gas exchange occurs. Accordingly, atelectasis can decrease the level of oxygen in the blood. The body compensates for a small amount of atelectasis by constricting the blood vessels in the affected area. This constriction redirects blood flow to alveoli that are open so that gas exchange can occur.
A common cause of atelectasis is a blockage of one of the tubes (bronchi) that branch off from the trachea (windpipe) and lead to the lung tissue. The blockage may be caused by something inside the bronchus, such as a plug of mucus, a tumor, or an inhaled foreign object (such as a coin, piece of food, or a toy). Alternatively, the bronchus may be blocked by something pressing from the outside, such as a tumor or enlarged lymph nodes. Blockage from the outside can also occur if the pleural space (the space outside of the lung but inside of the chest) contains a large amount of fluid (pleural effusion) or air (pneumothorax—see Pleural and Mediastinal Disorders: Pneumothorax). When a bronchus or bronchiole becomes blocked, the air in the alveoli beyond the blockage is absorbed into the bloodstream, causing the alveoli to shrink and collapse. The area of collapsed lung may become infected because bacteria and white blood cells can build up behind (to the inside of) the blockage. Infection is particularly likely if atelectasis persists for several days or more. If atelectasis persists for months, the lung may not easily re-expand.
Any condition that decreases deep breathing or suppresses a person's ability to cough can cause or contribute to atelectasis. Large doses of opioids or sedatives can decrease deep breathing. Atelectasis is common after general anesthesia, which temporarily suppresses a person's cough and drive to breathe. Atelectasis is particularly common after chest or abdominal surgery because the effects of receiving general anesthesia may be added to the pain of deep breathing, so people take only small breaths. Chest or abdominal pain from other causes (for example, from injury or pneumonia) also makes taking a deep breath painful. Certain neurologic conditions and chest deformities can limit chest movement and thus decrease deep breathing, as can abdominal swelling, immobility of the body, and some tight bandages. People who smoke or who have lung disorders (eg, chronic obstructive pulmonary disease, cystic fibrosis) have a greater risk of developing atelectasis.
The only symptom a person with atelectasis may feel is shortness of breath. The presence and severity of shortness of breath depend on how rapidly atelectasis develops and how much of the lung is affected. If atelectasis involves a small number of alveoli or develops slowly, symptoms may be mild or not even noticed. If a large number of alveoli are affected, particularly if atelectasis occurs rapidly, shortness of breath may be severe. The heart rate and breathing rate may increase, and sometimes the person may look bluish (a condition called cyanosis) because oxygen levels in the blood are low.
Symptoms may also reflect the disorder that caused atelectasis (for example, chest pain due to an injury) or a disorder that results from atelectasis (for example, chest pain with deep breathing, due to pneumonia).
Doctors suspect atelectasis based on a person's symptoms, the physical examination findings, and the setting in which the symptoms occurred. A chest x-ray that shows the airless area confirms the diagnosis. When bronchial blockage is suspected, computed tomography (CT), bronchoscopy (inserting a viewing tube into the bronchus), or both may be performed to find the cause, especially when the collapse persists despite treatment.
People who smoke can decrease their risk of atelectasis after surgery by stopping smoking, ideally 6 to 8 weeks before surgery. After surgery, people are encouraged to breathe deeply, cough regularly, and move about as soon as possible. The use of devices to encourage voluntary deep breathing (incentive spirometry) and certain exercises, including changing position to increase the drainage of lung mucus and other secretions, may help to prevent atelectasis.
Atelectasis may be prevented by making sure deep breathing occurs. Whenever possible, conditions that cause shallow breathing for long periods should be treated. Some people affected by these disorders may benefit from mechanical assistance with breathing. One method is continuous positive airway pressure, which delivers air or a mixture of air and oxygen through the nose or a face mask under continuous pressure, even during exhalation, to help ensure that the airways do not collapse and the lung stays expanded.
Treatment of atelectasis may involve making sure deep breathing occurs, relieving airway blockages, or both.
Sometimes blockages can be relieved when a patient's airway is suctioned by a health care practitioner. A blockage that cannot be removed by suctioning may require removal by bronchoscopy (see Diagnosis of Lung Disorders: Bronchoscopy). Sometimes other methods are necessary. For example, if a tumor is blocking an airway, the obstruction can sometimes be relieved by surgery, radiation therapy, chemotherapy, or laser therapy.
Symptoms and complications of atelectasis may require treatment. Patients may require supplemental oxygen, continuous positive airway pressure, or, rarely, insertion of a breathing tube (endotracheal intubation) and mechanical ventilation. If a bacterial infection is suspected, antibiotics are almost always given.
Last full review/revision February 2008 by Joshua O. Benditt, MD