Aspiration Pneumonia and Chemical Pneumonitis
Aspiration pneumonia is lung infection caused by inhaling mouth secretions, stomach contents, or both. Chemical pneumonitis is lung irritation caused by inhalation of substances toxic to the lungs.
Aspiration pneumonia and chemical pneumonitis are often considered together because they both involve lung inflammation caused by inhaling substances that irritate the lungs. The inflammation makes the lungs more susceptible to bacterial infection.
Tiny particles from the mouth frequently dribble or are inhaled (aspirated) into the airways. Usually they are cleared out by normal defense mechanisms (such as coughing) before they can get into the lungs and cause inflammation or infection. When such particles are not cleared (because of impaired defense mechanisms and/or because the volume of aspirated material is large), aspiration pneumonia can develop.
Material aspirated from the mouth and throat are more likely to contain bacteria, which can cause infectious pneumonia. Material aspirated from the stomach is usually very acidic and can severely damage the lungs even before infection develops.
People who are especially at risk of aspiration pneumonia include people who
Have trouble swallowing (as may happen due to a stroke)
Are intoxicated by alcohol or drugs
Are unconscious due to anesthesia, sedative drugs, or a medical condition
Have undergone dental procedures, respiratory, or digestive procedures
Have gastroesophageal reflux disease
Symptoms of aspiration pneumonia do not begin for at least a day or two. The most common symptom is a cough that produces sputum (thick or discolored mucus). The sputum may smell foul. Other symptoms of aspiration pneumonia include
Doctors usually make the diagnosis based on finding signs or symptoms in people who have any of the risk factors described above. A chest x-ray confirms the diagnosis of pneumonia. If the x-ray shows an abnormality in the bottom of the lungs (a common location for aspirated material), aspiration is more likely to be the cause.
Treatment requires antibiotics. Many antibiotics, including clindamycin, amoxicillin/clavulanate, ampicillin/sulbactam, and imipenem, can be used. If the person inhaled a large, solid piece of food, doctors may need to use bronchoscopy to remove it.
For people who have conditions that increase their risk of aspiration, doctors may stop or reduce the dosage of drugs that cause sedation. Raising the head of the bed slightly and having the person consume specific food textures or thickened liquids also help reduce the risk of aspiration. A speech pathologist may teach the person specific swallowing techniques (for example, swallowing while tucking the chin toward the chest) to further reduce the risk of aspiration.
Chemical pneumonitis occurs when a person inhales (aspirates) material that is toxic to the lungs. The problem is more the result of irritation than infection. A commonly inhaled toxic material is stomach acid, so that chemical pneumonitis may result whenever a person inhales what has been vomited up. Inhalation of vomit can occur when a person who vomits is not completely awake, as can happen after a seizure or a drug or alcohol overdose or when a person awakens from anesthesia.
Chemical pneumonitis may also be caused by inhalation of laxative oils (such as mineral, castor, and paraffin oils) and hydrocarbons (such as gasoline, kerosene, and petroleum products).
Sudden shortness of breath and a cough develop within minutes or hours. Other symptoms may include fever and pink frothy sputum. In less severe cases, the symptoms of aspiration pneumonia may occur a day or two after inhalation of the toxin.
The diagnosis of chemical pneumonitis is usually obvious to doctors from the sequence of events if this information is available. Chest x-rays and measuring the concentration of oxygen in a blood sample may help. When the diagnosis remains unclear, doctors sometimes do bronchoscopy.
Treatment consists of oxygen therapy and, if necessary, temporary assistance from a breathing machine via a tube placed in the throat. The windpipe (trachea) may be suctioned to clear secretions and aspirated food particles out of the airways. Bronchoscopy may also be used for this purpose.
Although antibiotics are not usually effective for this condition, they are often given because doctors cannot easily distinguish chemical pneumonitis from a bacterial aspiration pneumonia. Up to 30 to 50% of people with serious chemical pneumonitis due to inhaled stomach acid die.
Doctors may recommend various strategies to help prevent chemical pneumonitis in people at risk. These include stopping or reduce the dosage of drugs that cause sedation. They may also suggest that the head of the bed be raised slightly to prevent food, liquid or acid from the stomach from moving up into the throat and then down into the lungs. A speech pathologist may recommend specific food textures or thickened liquids and teach the person specific swallowing techniques (for example, swallowing while tucking the chin toward the chest) to reduce the risk of food and liquids going down into the lungs.