Aspiration pneumonia and pneumonitis

Aspiration pneumonia and pneumonitis are caused by aspiration of toxic substances, usually gastric contents, into the lungs. The result may be undetectable or chemical pneumonitis, bacterial pneumonia, or airway obstruction. Symptoms of aspiration pneumonia include cough and shortness of breath. Diagnosis is based on clinical presentation and chest radiography. Treatment of aspiration pneumonia and prognosis depend on the substance aspirated.

Aspiration of fluid (eg, due to drowning) or solid food causes a range of complications, from atelectasis to hypoxemia and death. The diagnosis is obvious from the history; treatment involves aspiration of the fluid or bronchoscopic removal of the food if possible. If the food cannot be completely removed, glucocorticoids are sometimes given, but their effectiveness in these situations is unproven.

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Causes aspiration pneumonia

Many substances are either directly toxic to the lung or stimulate an inflammatory response after aspiration; gastric acid is an example, but other substances can also cause chemical pneumonitis, notably petroleum products (petroleum jelly) and liquid oils (mineral oil or kerosene), which cause lipoid pneumonia.

Lung injury from gastric aspiration is primarily due to the presence of hydrochloric acid, although other components of the gastric contents (food, activated charcoal taken in the treatment of overdoses) may also have an aggressive effect. Gastric acid causes a chemical burn of the airways and lung, leading to rapid bronchospasm, atelectasis, edema, and alveolar hemorrhage. Symptoms include acute dyspnea with cough, sometimes productive of pink frothy sputum; tachypnea; tachycardia; fever; diffuse crackles. Chest radiography shows diffuse infiltrates, often but not exclusively in dependent segments, while pulse oximetry and blood gas analysis show hypoxemia. Treatment is supportive; mechanical ventilation is often required. Antibiotics are usually given to patients in whom gastric aspiration is confirmed by reliable evidence. The syndrome may resolve spontaneously, usually within a few days; may progress to acute respiratory distress syndrome and/or may be complicated by bacterial superinfection.

Aspiration of oils or petroleum jelly causes exogenous lipoid pneumonia, which is characterized histologically by chronic granulomatous inflammation with fibrosis. It is often asymptomatic and is discovered incidentally on chest radiography or may present with low grade fever, gradual weight loss, and wheezing. Chest radiographic findings are variable; consolidation, cavitation, interstitial or nodular infiltration, pleural effusion, and other changes may progress slowly. Treatment consists of reversal of the toxic effect.

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Risk factors

The risk of aspiration occurs in cases of impaired consciousness, difficulty swallowing, vomiting, the presence of gastrointestinal or endotracheal tubes or procedures, and gastroesophageal reflux disease.

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Symptoms aspiration pneumonia

Aspiration pneumonia and abscess have similar symptoms - chronic mild dyspnea, fever, weight loss and cough, productive, with the release of putrid sputum of an unpleasant taste. Signs of poor oral hygiene may be present.

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Complications and consequences

Healthy individuals often aspirate small amounts of oral secretions, but normal defense mechanisms clear the airways without complications. Aspiration of large amounts or aspiration in a patient with compromised pulmonary defenses often results in pneumonia and/or abscess.

Aspiration can cause inflammation of the lung (chemical pneumonitis), infection (bacterial pneumonia or abscess), or airway obstruction. Most episodes of aspiration cause minor symptoms or pneumonitis rather than infection or obstruction.

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Diagnostics aspiration pneumonia

Chest radiography reveals infiltration, often but not exclusively in the dependent lung segments, i.e., the superior segment of the lower lobe or the posterior segment of the upper lobe. Anaerobes are often isolated from the sputum, but it is unclear whether these are the primary pathogens that should be treated or are simply one of several organisms causing the infection.

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Treatment aspiration pneumonia

Treatment of aspiration pneumonia is with clindamycin 450 to 900 mg IV every 8 hours, then 300 mg orally 4 times daily until fever and clinical symptoms resolve. Penicillin (either penicillin G 1 to 2 million units every 4 to 6 hours or amoxicillin 0.5 to 1 g orally 3 times daily) plus metronidazole 500 mg orally 3 times daily or amoxicillin-clavulanate 1.2 g IV 3 times daily, then 875 mg/125 mg orally twice daily or imipenem 500 mg IV 4 times daily are acceptable alternatives to clindamycin. Duration of treatment is usually 1 to 2 weeks unless pneumonia is complicated by lung abscess formation; In this case, treatment of aspiration pneumonia may continue for 6 weeks to 3 months. Empyema is another common complication.