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Aspiration pneumonia is a form of bronchopneumonia, an inflammation of the bronchioles of the lungs, caused by foreign matter that is aspirated, or breathed, into the lungs. The condition is often caused by food or pill particles, saliva, nasal secretions, or bile. It can be complicated by high acidity of the aspirated matter and by the presence of anaerobic bacteria normally found in the human mouth.
The lungs contain a branching structure of airways called bronchi. The smaller branches of the bronchi, beginning at the point where there is no more cartilage in the airway, are called the bronchioles. The bronchioles terminate at the alveolar sacs or alveoli, the site of gas exchange in the lungs, where the blood is oxygenated. The bronchioles and alveoli are the affected structures in aspiration pneumonia.
Aspiration pneumonia, like other forms of bronchopneumonia, is an acute inflammation of the bronchioles that leads to an immune response in which the alveoli fill with fluid. This results in reduced air space in the lungs and chest congestion. Chemical inflammation can also be present if an acidic substance is breathed into the lungs. The location of pneumonia in the lungs is dependent on gravity, so that it appears lower in the lungs in patients that aspirate in an upright position, and higher in the lungs in patients who aspirate in a prone position.
This type of pneumonia is often caused by impaired swallowing, such as in a person who is intoxicated or who has suffered neurological damage like a stroke. It is also a possible complication of surgery under general anaesthesia. Patients undergoing general anaesthesia are therefore recommended to refrain from eating or drinking anything for a number of hours before surgery.
The bacteria most commonly present in aspiration pneumonia are those normally found in the mouth. These include bacteria of the genera Bacteriodes, Prevotella, and Peptostreptococcus. Such bacteria are anaerobic, meaning they do not need oxygen to survive, but aerotolerant, meaning they can live in the presence of oxygen. Bacterial pathogens can also contribute to aspiration pneumonia. These may include Fusobacterium species, as well as aerobic bacteria that require oxygen to survive, such as Streptococcus pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, and Haemophilus influenzae.
Aspiration pneumonia causes symptoms including cough, fever, pain and weakness, shortness of breath, headache, nausea, and weight loss. The first line of treatment is stabilizing the airway and providing lost fluids and electrolytes intravenously. The airway can be stabilized through suctioning and, if needed, through the use of a breathing tube. Antibiotics or corticosteroids can be used to fight bacterial infection in the lungs.