Aspiration pneumonitis and pneumonia are caused by inhaling toxic and/or irritant substances, most commonly large volumes of upper airway secretions or gastric contents, into the lungs. Chemical pneumonitis, bacterial pneumonia, or airway obstruction can occur. Symptoms include cough and dyspnea. Diagnosis is based on clinical presentation and chest x-ray findings. Treatment and prognosis differ depending on the substance that was aspirated.
(See also Overview of Pneumonia.)
Aspiration can cause lung inflammation (chemical pneumonitis), infection (bacterial pneumonia or lung abscess), or airway obstruction (because of mechanical obstruction or reflex airway spasm). 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 level of consciousness (eg, due to drug overdose, alcohol intoxication, seizures)
Dysphagia (due to esophageal and/or laryngeal disorders, neurologic diseases)
Vomiting
Gastrointestinal devices and procedures (eg, nasogastric tube placement)
Respiratory devices and procedures (eg, endotracheal tube placement—see Ventilator-Associated Pneumonia)
Pathophysiology
Chemical pneumonitis
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 contentsatelectasis, and edema. This syndrome may resolve spontaneously, usually within a few days, or may progress to acute respiratory distress syndrome. Bacterial superinfection occurs in about 25% of patients.
Aspiration pneumonia
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. The clinical setting where aspiration occurs can determine the microbiology of aspiration, with streptococci and anaerobes more frequent in community-acquired pneumonia and gram-negative bacilli and methicillin-resistant Staphylococcus aureus (MRSA) dominating in hospital-acquired pneumonia. Periodontal disease predisposes to anaerobic infection.
Symptoms and Signs
Symptoms and signs include
Cough
Fever
Dyspnea
Chest discomfort
Chemical pneumonitis caused by gastric contents causes acute dyspnea with cough that is sometimes productive of pink frothy sputum, tachypnea, tachycardia, fever, diffuse or localized 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. Aspiration pneumonia can have a variable onset, and in cases caused by anaerobes, the evolution can be subacute.
Diagnosis
Chest x-ray
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 aspiration pneumonia and lung abscess. In lung abscesses, contrast-enhanced CT will show a round lesion filled with fluid or with an air-fluid level. Aspiration pneumonitis and pneumonia are distinguished by their clinical course and are indistinguishable by imaging.
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. A CT scan can show fat attenuation within the consolidative opacities and nodules.
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.
Selected patients with unexplained aspiration pneumonitis and aspiration pneumonia should be tested for an underlying swallowing disorder.
Treatment
Supportive treatment
Antibiotics
Treatment of aspiration pneumonitis is supportive, often involving supplemental oxygen and mechanical ventilation. Antibiotics are often are given to patients with witnessed or known gastric aspiration; however, studies have not supported this practice. A preferred approach is close observation with antibiotics being prescribed if the clinical course suggests subsequent bacterial superinfection. Early empiric antibiotics can also be stopped if patients improve rapidly.
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 with significant disease.
Treatment of lung abscess is with antibiotics and sometimes percutaneous or surgical drainage. Many clinicians continue antibiotic treatment until the chest radiograph shows complete resolution or only a small, stable, residual abnormality.
Treatment references
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
2. Mandell LA, Niederman MS: Aspiration Pneumonia. N Engl J Med 380(7):651–663, 2019. doi:10.1056/NEJMra1714562
Prevention
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 medications and elevation of the head of the bed to > 30 degrees may help. Sedating medications should be stopped.
Patients with dysphagia (due to stroke or other neurologic conditions) have long been recommended to follow diets with thick textures to attempt to reduce the risk of aspiration; however, there is little firm evidence that this approach 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.
Key Points
Some patients with unexplained aspiration pneumonitis and aspiration pneumonia should be evaluated 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.
