The natural tendency for open air spaces such as the alveoli to collapse is countered by the following:
Surfactant (which maintains surface tension)
Continuous breathing (which keeps the alveoli open)
Intermittent deep breathing (which releases surfactant into the alveoli)
Periodic coughing (which clears the airways of secretions)
Major consequences of atelectasis include underventilation (with hypoxia and ventilation/perfusion [V/Q] mismatch) and pneumonia.
Etiology of Atelectasis
The most common factors that can cause atelectasis include the following:
Intrinsic obstruction of airways (eg, by foreign body, tumor, mucous plug)
Suppression of respiration or cough (eg, by general anesthesia, oversedation, pain)
Supine positioning, particularly in obese patients and those with cardiomegaly
Compression or collapse of lung parenchyma (eg, by large pleural effusion Pleural Effusion Pleural effusions are accumulations of fluid within the pleural space. They have multiple causes and usually are classified as transudates or exudates. Detection is by physical examination and... read more or pneumothorax Pneumothorax Pneumothorax is air in the pleural space causing partial or complete lung collapse. Pneumothorax can occur spontaneously or result from trauma or medical procedures. Diagnosis is based on clinical... read more )
Thoracic and abdominal surgeries are very common causes because they involve general anesthesia, opioid use (with possible secondary respiratory depression), and often painful respiration. A malpositioned endotracheal tube can cause atelectasis by occluding a mainstem bronchus.
Less common causes of atelectasis include surfactant dysfunction and lung parenchymal scarring or tumor.
Symptoms and Signs of Atelectasis
Atelectasis itself is asymptomatic unless hypoxemia or pneumonia Overview of Pneumonia Pneumonia is acute inflammation of the lungs caused by infection. Initial diagnosis is usually based on chest x-ray and clinical findings. Causes, symptoms, treatment, preventive measures, and... read more develops. Symptoms of hypoxemia tend to be related to acuity and extent of atelectasis. With rapid, extensive atelectasis, dyspnea or even respiratory failure can develop. With slowly developing, less extensive atelectasis, symptoms may be mild or absent.
Pneumonia may cause cough, dyspnea, and pleuritic pain. Pleuritic pain may also be due to the disorder that caused atelectasis (eg, chest trauma, surgery).
Signs are often absent. Decreased breath sounds in the region of atelectasis and possibly dullness to percussion and decreased chest excursion are detectable if the area of atelectasis is large. Often it is discovered only on chest imaging (eg, x-ray or CT).
Diagnosis of Atelectasis
Atelectasis should be suspected in patients who have any unexplained respiratory symptoms and who have risk factors, particularly recent major surgery. Atelectasis that is clinically significant (eg, that causes symptoms, increases risk of complications, or meaningfully affects pulmonary function) is generally visible on chest x-ray; findings can include lung opacification and/or loss of lung volume.
If the cause of atelectasis is not clinically apparent (eg, if it is not recent surgery or pneumonia seen on chest x-ray) or another disorder is suspected (eg, pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more , tumor), other tests, such as bronchoscopy or chest computed tomography (CT), may be necessary.
Treatment of Atelectasis
Maximizing cough and deep breathing
If obstruction by tumor or foreign body is suspected, bronchoscopy
Evidence for the efficacy of most treatments for atelectasis is weak or absent. Nonetheless, commonly recommended measures include chest physiotherapy Chest Physiotherapy Chest physiotherapy consists of external mechanical maneuvers, such as chest percussion, postural drainage, and vibration, to augment mobilization and clearance of airway secretions. It is indicated... read more to help maintain ventilation and clearance of secretions, and encouragement of lung expansion techniques such as directed cough, deep breathing exercises, and use of an incentive spirometer. In ambulatory patients, exercise (eg, walking) is a desirable way to promote deep breathing.
For patients who are not intubated and do not have excessive secretions, continuous positive airway pressure may help. For patients who are intubated and mechanically ventilated Overview of Mechanical Ventilation Mechanical ventilation can be Noninvasive, involving various types of face masks Invasive, involving endotracheal intubation Selection and use of appropriate techniques require an understanding... read more , positive end-expiratory pressure and/or higher tidal volume ventilation may help.
Avoiding oversedation helps ensure ventilation and sufficient deep breathing and coughing. However, severe pleuritic pain may impair deep breathing and coughing and may be relieved only with opioids. Thus, many clinicians prescribe opioid analgesics in doses sufficient to relieve pain and advise patients to consciously cough and take deep breaths periodically. In certain postoperative patients, epidural analgesia or an intercostal nerve block may be used to relieve pain without causing respiratory depression. Antitussive therapy should be avoided.
Most importantly, the cause of atelectasis (eg, mucous plug, foreign body, tumor, mass, pulmonary effusion) should be treated. For persistent mucous plugging, nebulized dornase alfa and sometimes bronchodilators are tried. N-Acetylcysteine is usually avoided because it can cause bronchoconstriction. If other measures are ineffective or if a cause of obstruction other than mucous plugging is suspected, bronchoscopy should be done.
Prevention of Atelectasis
Smokers can decrease their risk of postoperative atelectasis by stopping smoking Smoking Cessation Most smokers want to quit and have tried doing so with limited success. Effective interventions include cessation counseling and drug treatment, such as varenicline, bupropion, or a nicotine... read more , ideally at least 6 to 8 weeks before surgery. Drug treatment for patients with chronic lung disorders (eg, chronic obstructive pulmonary disease [COPD] Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more ) should be optimized before surgery. Preoperative inspiratory muscle training (including incentive spirometry) should be considered for patients scheduled for thoracic or upper abdominal surgery.
After surgery, early ambulation and lung expansion techniques (eg, coughing, deep breathing exercises, incentive spirometry) may also decrease risk.
Atelectasis is reversible collapse of lung tissue with loss of volume; common causes include intrinsic or extrinsic airway compression, hypoventilation, and a malpositioned endotracheal tube.
A large area of atelectasis may cause symptomatic hypoxemia, but any other symptoms are due to the cause or a superimposed pneumonia.
Diagnosis is by chest x-ray; if the cause is not clinically apparent, bronchoscopy or chest computed tomography may be needed.
Treatment involves maximizing coughing, deep breathing, and, whenever possible, walking.