Tiny particles from the mouth frequently dribble into the airways, but usually they're cleared out by normal defense mechanisms before they can get into the lungs or cause inflammation or infection. When such particles aren't cleared, they can cause pneumonia. People who are debilitated, intoxicated by alcohol or drugs, or unconscious from anesthesia or a medical condition are especially at risk for this type of pneumonia. Even a healthy person who inhales a large amount of material, as may happen during vomiting, can develop pneumonia.
Chemical pneumonitis occurs when the inhaled (aspirated) material is toxic to the lungs; the problem is more the result of irritation than infection. A commonly inhaled toxic material is stomach acid. The immediate result is sudden shortness of breath and a rapid heart rate. Other symptoms include a fever, pink frothy sputum, and a bluish tinge to the skin caused by poorly oxygenated blood (cyanosis).
Chest x-rays and measurements of oxygen and carbon dioxide concentration in arterial blood may help a doctor make the diagnosis, but usually it's obvious from the sequel of events. Treatment consists of oxygen therapy and mechanical ventilation if necessary. The trachea may be suctioned to clear secretions and aspirated particles out of the airways.
Sometimes, antibiotics are given to prevent infection. Generally, people with chemical pneumonitis either recover rapidly, progress to acute respiratory distress syndrome, or develop a bacterial infection. About 30 to 50 percent of people with chemical pneumonitis die.
Bacterial aspiration is the most common form of aspiration pneumonia. It's usually caused by bacteria swallowed and inhaled into the lungs.
Mechanical obstruction of the airways may be caused by aspiration of particles or objects. Young children are most at risk because they often put objects into their mouth and may aspirate small toys or parts of toys. Obstruction can also occur in adults, typically when meat is aspirated while eating. If an object becomes stuck high in the trachea, the person may be unable to breathe or speak. If the object isn't removed immediately, the person will quickly die. The Heimlich maneuver, performed to dislodge the object, can save the person's life. If an object gets stuck lower in the airways, an irritating chronic cough and recurring infections may result. The object is usually removed during bronchoscopy (a procedure using an instrument that allows a doctor to view the airway and remove samples and foreign material).