(See also Overview of 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 .)
Aspiration can cause lung inflammation (chemical pneumonitis), infection (bacterial 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 or lung abscess Lung Abscess Lung abscess is a necrotizing lung infection characterized by a pus-filled cavitary lesion. It is most commonly caused by aspiration of oral secretions by patients who have impaired consciousness... read more ), or airway obstruction Etiology Respiratory arrest and cardiac arrest are distinct, but inevitably if untreated, one leads to the other. (See also Respiratory Failure, Dyspnea, and Hypoxia.) Interruption of pulmonary gas exchange... read more (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 Drowning Drowning is respiratory impairment resulting from submersion in a liquid medium. It can be nonfatal (previously called near drowning) or fatal. Drowning results in hypoxia, which can damage... read more 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)
Gastrointestinal devices and procedures (eg, nasogastric tube placement)
Respiratory devices and procedures (eg, endotracheal tube placement—see Ventilator-Associated Pneumonia Ventilator-Associated Pneumonia Ventilator-associated pneumonia (VAP) develops at least 48 hours after endotracheal intubation. The most common pathogens are gram-negative bacilli and Staphylococcus aureus; antibiotic-resistant... read more )
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 Hydrocarbon Poisoning Hydrocarbon poisoning may result from ingestion or inhalation. Ingestion, most common among children < 5 years, can result in aspiration pneumonitis. Inhalation, most common among adolescents... read more ).
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 Atelectasis Atelectasis is collapse of lung tissue with loss of volume. Patients may have dyspnea or respiratory failure if atelectasis is extensive. They may also develop pneumonia. Atelectasis is usually... read more , and edema. This syndrome may resolve spontaneously, usually within a few days, or may progress to acute respiratory distress syndrome Acute Hypoxemic Respiratory Failure (AHRF, ARDS) Acute hypoxemic respiratory failure is defined as severe hypoxemia (PaO2 (See also Overview of Mechanical Ventilation.) Airspace filling in acute hypoxemic respiratory failure (AHRF) may result... read more . Bacterial superinfection occurs in about 25% of patients.
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 Lung Abscess Lung abscess is a necrotizing lung infection characterized by a pus-filled cavitary lesion. It is most commonly caused by aspiration of oral secretions by patients who have impaired consciousness... read more . 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 Etiology ) 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 Community-Acquired Pneumonia Community-acquired pneumonia is defined as pneumonia that is acquired outside the hospital. The most commonly identified pathogens are Streptococcus pneumoniae, Haemophilus influenzae... read more and gram-negative bacilli and methicillin-resistant Staphylococcus aureus (MRSA) dominating in hospital-acquired pneumonia Hospital-Acquired Pneumonia Hospital-acquired pneumonia (HAP) develops at least 48 hours after hospital admission. The most common pathogens are gram-negative bacilli and Staphylococcus aureus; antibiotic-resistant... read more . Periodontal disease predisposes to anaerobic infection.
Symptoms and Signs
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 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.
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 of aspiration pneumonitis is supportive, often involving supplemental oxygen and mechanical ventilation 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 . 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.
For aspiration pneumonia, a beta-lactam/beta-lactamase inhibitor is recommended; moxifloxacin or clindamycin is reserved for use in patients who are allergic to penicillin (1 Treatment references 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... read more ). If aspiration occurs in the hospital setting, a carbapenem or piperacillin/tazobactam can be used; medications effective against MRSA are added if risk factors for that pathogen are present. Duration of treatment is usually 1 week (2 Treatment references 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... read more ).
Treatment of lung abscess Treatment Lung abscess is a necrotizing lung infection characterized by a pus-filled cavitary lesion. It is most commonly caused by aspiration of oral secretions by patients who have impaired consciousness... read more 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.
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
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.
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.
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