Epidemiology
Aspiration can occur regardless of sex, age group, or ethnicity.[9] True incidence of aspiration pneumonia is difficult to assess because many cases of community-acquired pneumonia (CAP) or hospital-acquired pneumonia are probably the result of aspiration that was undiagnosed. However, some studies suggest that aspiration pneumonia may be the cause of as many as 5% to 15% of CAP cases.[10][11] Aspiration pneumonia predominantly affects older adults, and occurs especially in those with swallowing dysfunction, impaired conscious level, neuromuscular diseases, or mechanical impairment of the oropharynx and digestive tract.[3][4][9] It is the most common cause of death among patients with swallowing dysfunction related to neurological disease.[8]
Risk factors
Seen in neurological conditions, in particular, especially stroke. As many as 40% to 70% of stroke patients have swallowing dysfunction and many of them have silent aspiration.[3][4][8][12][18]
Other neurological conditions that may cause swallowing dysfunction include Parkinson’s disease, motor neuron disease, and dementia, as well as myopathies such as myasthenia gravis and myotonic dystrophy.
Swallowing dysfunction in combination with inability to clear the laryngo-pharynx by coughing increases the risk of aspiration pneumonia.[19]
Upper gastrointestinal surgery and oesophageal abnormalities predispose to aspiration.[3][12][13] Gastro-oesophageal reflux disease, hiatal hernia, other gastrointestinal motility disorders, and conditions that affect gastric emptying (obesity and pregnancy) increase the risk of regurgitation and pulmonary aspiration.[20]
Aspiration of oropharyngeal bacteria can occur around the endotracheal tube, although this is typically called ventilator-associated pneumonia, rather than aspiration pneumonia.[21] Risk of aspiration may be especially high immediately after removal of the tube due to:[8][22]
Pooling of secretions
Altered laryngeal movement during swallowing
Laryngeal desensitisation.
Many patients with a tracheostomy have a history of head and neck cancer and have had previous upper airway surgery and radiation, which further increases their risk of aspiration.[23]
May occur in patients with upper airway problems (such as pharyngeal pouches and vocal cord palsies) and neuromuscular disease.
Swallowing dysfunction in combination with inability to clear the laryngopharynx by coughing increases the risk of aspiration pneumonia.[19]
Aspiration commonly occurs after chemoradiation for head and neck cancers. Risk factors for the subsequent development of pneumonia are tracheobronchial aspiration and a positive smoking history.[27]
Many patients with head and neck cancers also have a tracheostomy and previous upper airway surgery, which further increases their risk of aspiration.[23]
Aspiration may occur due to vomiting or aspiration of blood or teeth.
Aspiration pneumonia is a major cause of death in patients with learning disability and disproportionately represented in this population.[31] Despite this, most aspiration pneumonia occurs in patients without learning disability. Silent microaspiration is in common in children with learning disabilities.[3][32]
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