(See also Overview of Pneumonia.)
Aspiration can cause lung inflammation (chemical pneumonitis), infection (bacterial pneumonia or lung abscess), or airway obstruction. Microaspiration of small quantities of upper airway secretions is common; however, this aspirated material is cleared by normal lung defense mechanisms. The term aspiration pneumonia is used when the ability to protect the lower airway is compromised and/or a large volume is aspirated. Drowning may also cause inflammation of the lungs.
Risk factors for aspiration include
Impaired cognition or level of consciousness
Impaired swallowing (such as occurs after some strokes or other neurologic diseases)
Gastrointestinal devices and procedures (eg, nasogastric tube placement)
Respiratory devices and procedures (eg, endotracheal tube placement—see Ventilator-Associated Pneumonia)
Multiple substances are directly toxic to the lungs or stimulate an inflammatory response when aspirated; gastric acid is the most common such aspirated substance, but others include petroleum products (particularly of low viscosity, such as petroleum jelly) and laxative oils (such as mineral, castor, and paraffin oil). Petroleum products and laxative oils can cause lipoid pneumonia. Aspirated gasoline and kerosene also cause a chemical pneumonitis (see Hydrocarbon Poisoning).
Gastric contents cause damage mainly due to gastric acid, although food and other ingested material (eg, activated charcoal as in treatment of overdose) are injurious in quantity. Gastric acid causes a chemical burn of the airways and lungs, leading to rapid bronchoconstriction, atelectasis, edema, and alveolar hemorrhage. This syndrome may resolve spontaneously, usually within a few days, or may progress to acute respiratory distress syndrome. Bacterial superinfection occurs in about 25%.
Healthy people commonly aspirate small amounts of oral secretions, but normal defense mechanisms usually clear the inoculum without sequelae. Aspiration of larger amounts, or aspiration in a patient with impaired pulmonary defenses, often causes pneumonia and/or a lung abscess. Older patients tend to aspirate because of conditions associated with aging that alter consciousness (eg, sedative use) and other disorders (eg, neurologic disorders, swallowing disorders). Empyema (see Pleural Effusion) also occasionally complicates aspiration.
Gram-negative enteric pathogens and oral anaerobes are the most frequent pathogens in aspiration pneumonia.
Symptoms and signs include
Chemical pneumonitis caused by gastric contents causes acute dyspnea with cough that is sometimes productive of pink frothy sputum, tachypnea, tachycardia, fever, diffuse crackles, and wheezing. When oil or petroleum jelly is aspirated, pneumonitis may be asymptomatic and detected incidentally on chest x-ray or may manifest with low-grade fever, gradual weight loss, and crackles.
For aspiration pneumonia, chest x-ray shows an infiltrate, frequently but not exclusively, in the dependent lung segments, ie, the superior or posterior basal segments of a lower lobe or the posterior segment of an upper lobe. For aspiration-related lung abscess, chest x-ray may show a cavitary lesion. Contrast-enhanced computed tomography (CT) is more sensitive and specific for lung abscess and will show a round lesion filled with fluid or with an air-fluid level. In patients with oil or petroleum jelly aspiration, chest x-ray findings vary; consolidation, cavitation, interstitial or nodular infiltrates, pleural effusion, and other changes may be slowly progressive.
Signs of ongoing aspiration may include frequent throat clearing or a wet-sounding cough after eating. Sometimes no signs are present, and ongoing aspiration is only diagnosed via modified barium esophagography done to rule out an underlying swallowing disorder.
Treatment is supportive, often involving supplemental oxygen and mechanical ventilation. Antibiotics (a beta-lactam/beta-lactamase inhibitor or clindamycin) often are given to patients with witnessed or known gastric aspiration because of the difficulty in excluding bacterial infection as a contributing or primary factor; however, if patients improve rapidly, antibiotics can be stopped. Patients with apparently mild cases can also be observed without initiating antibiotics.
Toxic substances that may cause lipoid pneumonia should be avoided. Anecdotal reports suggest systemic corticosteroids may be beneficial in patients with oil or petroleum jelly aspiration.
For aspiration pneumonia, a beta-lactam/beta-lactamase inhibitor is recommended, with clindamycin being reserved for penicillin allergic patients (1). If aspiration occurs in the hospital setting, a carbapenem or piperacillin/tazobactam can be used; drugs effective against methicillin-resistant Staphylococcus aureus are added if risk factors for that pathogen are present. Duration of treatment is usually 1 to 2 weeks.
Treatment of lung abscess is with antibiotics and sometimes percutaneous or surgical drainage. Many practitioners continue antibiotic treatment until the chest radiograph shows complete resolution or only a small, stable, residual abnormality.
1. Metlay JP, Waterer GW, Long AC, et al: Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America. Am J Respir Crit Care Med 200(7): e45–e67, 2019. https://doi.org/10.1164/rccm.201908-1581ST
Strategies to prevent aspiration are important to care and overall clinical outcome. For patients with decreased level of consciousness, avoidance of oral feeding and oral drugs and elevation of the head of the bed to > 30 degrees may help. Sedating drugs should be stopped. Patients with dysphagia (due to stroke or other neurologic conditions) have long been recommended to follow diets with specialized textures to attempt to reduce the risk of aspiration however there is little firm evidence that this is effective. A speech pathologist may be able to train patients in specific strategies (chin tuck, etc.) to reduce the risk of aspiration. For patients with severe dysphagia, a percutaneous gastrostomy or jejunostomy tube is often used, although it is not clear whether this strategy truly reduces the risk of aspiration because patients can still aspirate oral secretions and may have reflux of gastrostomy tube feedings.
Optimization of oral hygiene and regular care by a dentist may help prevent development of pneumonia or abscess in patients who repeatedly aspirate.
Patients with aspiration pneumonitis and aspiration pneumonia should be tested for an underlying swallowing disorder.
Aspiration pneumonia should be treated with antibiotics; treatment of aspiration pneumonitis is primarily supportive.
Secondary prevention of aspiration using various measures is a key component of care for affected patients.