ICU Chest Films > Lung Processes > Aspiration Syndromes > Aspiration of Gastric Acid

Aspiration of Gastric Acid

Aspiration of gastric acid is also known as Mendelson's Syndrome, it is the most common type of aspiration. The degree of irritation to the lung is directly dependent on the acidity and volume of the aspirated fluid. The lung responds to pH < 2.5 with severe bronchospasm and the release of inflammatory mediators. The initial result is a chemical pulmonary edema. Secondary infection may or may not result. The clinical manifestations occur within minutes of the event and include cough, dyspnea, wheezing and diffuse crackles. Fever and an elevated white count will occur in the majority of patients. The consequences of aspiration range from shock to uncomplicated resolution of the initial event. The chest film in patients that progress to pneumonitis will reveal pulmonary consolidation within the first two days. The consolidation is usually perihilar and bilateral, though asymmetric. The radiographic findings begin to stablize or resolve by the third day. Some patients' radiographs will show worsening of the consolidation as well as findings associated with pneumonia, including pleural effusions and abscess formation. Aspiration may also cause ARDS.

Which of the following is NOT one of the four most common causes of lung abcess formation?
Aspiration
Septic emboli
Viral pneumonia
Post-obstructive infection

Aspirated particulate matter or contents with a neutral pH, such as bilious material, will not cause a chemical pneumonitis. Instead, they cause direct bronchial irritation and focal volume loss secondary to bronchial obstruction. These events seldom proceed to pulmonary consolidation. However, aspiration of infected material may lead to pneumonia.