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An infectious process due to inhalation of pathogenic bacteria from inhalation of oropharyngeal secretions.
The pathological passage of fluid or substances below the level of the vocal cords into the lower airways.
It is not a distinct entity but part of a continuum that also includes community and hospitalized acquired pneumonias.
It is considered an acute event and can result in infectious pneumonia, chemical pneumonitis, or even respiratory failure from the acute respiratory distress syndrome.
It is estimated that it accounts for 5-15% of cases of community acquired pneumonia.
Robust diagnostic criteria are lacking and as a result studies of this disorder include heterogeneous patient populations.
Aspiration of small amounts of oropharyngeal secretions is normal in healthy persons during sleep, yet microaspiration is also the major pathogenetic mechanism of most pneumonias.
Large volume aspiration, known as macroaspiration, of colonized oropharyngeal or upper gastrointestinal content is the sine qua non of aspiration pneumonia.
Macroaspiration is an essential feature of aspiration ammonia and chemical pneumonitis.
The variation of patient presentation and disease management includes bacterial virulence, risk of repeated events, and the site of acquisition such as a nursing home, hospital or community.
Anaerobes were previously the predominant pathogen in aspiration pneumonia , but more recently there is a shift to community and hospital acquired pneumonias, and anaerobes are recovered less frequently.
In community acquired cases, the main isolates were S. Pneumoniae, Staphylococcus aureus, Haemophilus influenza, and Enterobacteriaceae, whereas gram-negative bacilli including P. aeroginosa were found without anaerobes in hospital acquired cases.
Aspiration syndromes may involve the airways or a pulmonary parenchyma, resulting in clinical variations in presentation.
Aspiration pneumonia associated with a higher mortality than other forms of acquired pneumonia in the community.
In a survey of 4200 hospitals aspiration was documented in 4-26% of episodes of pneumonia.
Clinical presentation ranges from no symptoms to severe respiratory distress and respiratory failure, and the clinical consequences may develop acutely, subacutely, or slowly and progressively.
Aspiration into the lung can affect either the airway causing bronchospasm, asthma, and chronic cough or the lung parenchyma.
Aspiration pneumonia usually is acute with symptoms developing within hours to a few days after a sentinel event.
Anaerobic aspiration maybe subacute because of the less virulent bacteria, and Clnical features are difficult to distinguish from those of other bacterial pneumonia.
Aspiration of non-infectious material such as blood restoring body may be important.
Aspiration involving the lu g parenchyma areprimarily aspiration ammonia and chemical pneumonitis.
Aspiration pneumonia is an infection caused by specific microorganisms, whereas chemical pneumonitis is an inflammatory reaction to irritative gastric contents.
An acute chemical lung injury caused by inhalation of gastric contents.
The constituency and volume of aspirate material are important in the development of respiratory pathology and account for the different expressions of gastric aspiration-pneumonitis, ARDS, bronchospasm, bronchiolitis, and lung fibrosis.
If gastric contents do reflux into the esophagus, it must span the esophagus up to the pharynx by bypassing barriers of the EGJunction and lower esophageal sphincter but also esophageal peristalsis, which act to clear residual refluxate from the esophagus.
Initial treatment of gastric aspiration requires airway maintenance, management of airway edema or bronchospasm, and minimization of tissue damage: suctioning, bronchoscopy, intubation, mechanical ventilation, and ICU care.
In gastric aspiration routine therapy with glucocorticoids and antibiotics are not recommended unless the patient is taking acid suppressing medication or has small bowel obstruction.
In gastric aspiration antibiotics are withheld even in the presence of an infiltrate and are reassesse at 48 hours.
If the refluxate enters the pharynx, there must be sufficient volume and impairment in the cough or swallow reflexes to allow passage beneath the vocal cords into the lower airways-that is aspiration.
Aspiration is mostly attributed to the aspiration of gastric fluid, but it can result from duodenal, oral pharyngeal, or other injurious materials and the aspirate may contain other injureous materials such as microbes, bile or pepsin.
In patients with cardiac arrest, pneumonia develops within three days after the event in 65% of patients presumably from aspiration of gastric contents during resusfcitation and inhalation of oral secretions during bag-valve-mask ventilation and intubation.
Usually presents abruptly and can progress quickly to respiratory failure and rapid improvement within 48 hours.
A chest x-ray may be negative early in the course of aspiration ammonia.
5-15% of community-acquired pneumonias are aspiration pneumonias.
Aspiration of gastric contents tends to involve dependent parts of the lungs and can cause pulmonary infiltrates with effusions.
The most common cause of death in patients with dysphagia of neurologic origin and affects 300-600,000 people in the U.S. each year.
Common among nursing home residents causing 18% of nursing home-acquired pneumonia.
Occurs in approximately 10% of patients hospitalized with drug overdose.
Complicates 1 in 3000 general anesthetics given for surgery.
Accounts for 10-30% of all deaths associated with the administration of general anesthesia.
Chemical injury caused by injury of inhaled sterile gastric contents.
Chronic occult aspiration occurs with advanced age, dysphagia, altered mental status and with degenerative neurological disorders.
Bacteria make colonize various sites in the human oral cavity, such as the gingiva, dental plaque, and tongue.
Pathogenic bacteria, including gram-negative species are not seen in the normal host’s mouth , but may emerge in the elderly, as well as in patients in nursing homes or hospitals and those with nasogastric tubes.
May occur in absence of risk factors.
Aspiration is often the result of impaired swallowing, which allows oral or gastric contents, or both to have an ineffective lung especially in patients who have an ineffective cough reflex.
Large volume aspiration can occur with dysphasia, head and neck and esophageal cancers esophageal strictures and motility disorders, COPD and seizures.
Macroaspiration of gastric contents can lead to chemical pneumonitis but only with large volume, low-pH usually less than 2.5 aspiration.
Chronic occult pulmonary aspiration, ref2242ed to as silent aspiration, is considered more often in an outpatient setting and believed to contribute to the pathophysiology of multiple respiratory disorders, including pulmonary fibrosis, idiopathic pulmonary fibrosis, asthma, bronchiectasis, bronchiolitis, chronic bronchitis, pneumonia, chronic cough, and lung transplant rejection
Additional risk factors include degenerative neurological diseases such as multiple sclerosis, Parkinson’s disease, dementia, and impaired consciousness, particularly as a result of stroke and intracerebral hemorrhage, which can also impair cough clearance.
The frequency of stroke-associated pneumonia is related to the severity of the underlying neurologic process and is associated immune impairments, with higher rates among patients requiring intensive care.
Impaired consciousness can result from medications, drug overdoses, including narcotics, general anesthetics, and antidepressants, and alcohol.
Anti-psychotic medications increase the risk of aspiration pneumonia by a factor of 1.5.
Enteral feedings can lead to high volume aspiration, especially associated with gastric dysmotility, poor cough, and altered mental status.
In frail elderly patients dysphagia is associated with increased odds ratio for aspiration ammonia by a factor of 9.4, but when cerebrovascular disease was also present, the odds ratio increases to 12.9.
Approximately 25% of patients develop secondary bacterial pneumonia in the following 2-7 days manifested by worsening respiratory status or fever.
The mainstay of therapy is supportive care.
The administration of prophylactic antimicrobial therapy at the time of aspiration has not been demonstrated to prevent the development of pneumonia, and may expose patients to unnecessary therapy.
With the development of aspiration pneumonia following aspiration pneumonitis, a lung infection related to the aspiration of colonizing oral pharyngeal bacteria warrants in empirical antibiotic therapy to decrease mortality.
Aspiration pneumonitis and aspiration pneumonia may present with fever, tachypnea, cough, resprstory distress, and infiltrates.
The clearest difference between aspiration pneumonitis andaspiration pneumonia is the gradual onset of symptoms that can distinguish the two.
Aspiration lung disease is associated with several distinct clinical syndromes depending upon the volume and nature of the material that is aspirated, the number of events and the individual response to the insult.
Pneumonia is expected when there is no improvement within 48 hours, or occurrence of fever or worsening respiratory status two or more days following the aspiration event and that warrants initiation of antimicrobial therapy.
Healthy individuals may aspirate oral secretions in up to 50% of cases, during sleep.
Most individuals who aspirate do not come to clinical attention as they have adequate cough reflex and immune responses.
Aspiration pneumonia is related to aspirated acidic stomach contents causing chemical lung injury.
Lung injury from acid aspiration is due to the release of inflammatory mediators including chemokine, pro inflammatory cytokines and neutrophil recruitment.
Chemical pneumonitis is manifested by a sudden onset of dyspnea, hypoxemia, tachycardia, and diffuse wheezes or crackles on clinical examination.
Gastric acid aspiration usually does not cause bacterial infection, but can occur.
Neither chemical pneumonitis or aspiration pneumonia occur with tube feedings or aspirated blood, since the aspirate pH is usually high and uncontaminated by bacteria.
Acid suppressing therapy is associated with an increased risk of community or hospital acquired pneumonia, which is related to gastric overgrowth by gram negative bacteria, neutralization of gastric pH may reduce the risk of chemical pneumonitis.
In cases of unwitnessed aspiration, it may be difficult to distinguish among chemical pneumonitis, aspiration pneumonia, and aspiration of bland material.
And aspirated solid foreign body can obstruct the airway and lead to postobstructive pneumonia, complicating the distinction between bacterial pneumonia.
In a series of patients with foreign body aspiration the event was recognized only 29% of the time leading to a diagnostic delay of 1-3 months.
With foreign body aspiration chest x-rays reveal a right lung abnormality in 64% of the patients, and food material accounted for more than80% of the episodes.
Diagnosis is dependent upon the clinical history such as the witness of macroaspiration, risk factors, and compatible chest x-ray findings.
Chest x-ray findings include infiltrates in gravity dependent lung segment, such as the superior lower lobe or posterior upper lobes, if the patient is supine during the event, or basal segments of the lower lobe, if the patient is upright during the event.
Antibiotic selection depends on the site of the acquisition of the aspiration ammonia: the community, the hospital, or a long-term care facility and risk factors for infection with multicolor resistant organisms.
Risk factors for multidrug resistan pathogens include treatment with broad-spectrum antibiotics in the past 90 days and hospitalization for at least five days.
For most patients with community acquired cases treatment with ampicillin-sulbactam , a carbopenem, or a fluoroquinolone is effective.
Cllindamycin is added if an anaerobic infection risk is high, as it is for patients with severe periodontal disease and necrotizing pneumonia or lung abscess.
With mixed infection, elimination of aerobic pathogens usually alters the local redox potential, and eliminates anaerobes.
If bacterial resistance is a concern broader spectrum treatment with a Piperacin-tazobactam, cefepime, levofloxacin, imipenem, or merpenem either singlyor in combination is required.