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Aspiration pneumonia results from inhalation of stomach contents or secretions of the oropharynx leading to lower respiratory tract infection. In many healthy adults, very small quantities of aspiration occur frequently but the normal defence mechanisms (cough, lung cilia) remove the material with no ill effects. However, aspiration may cause:
- Chemical pneumonitis: chemical irritation of the lungs, which may progress to acute respiratory distress syndrome and/or bacterial infection. Acute aspiration of gastric contents into the lungs can produce an extremely severe and sometimes fatal illness. This has been termed Mendelson's syndrome and can complicate anaesthesia, particularly during pregnancy.
- Obstruction: large volumes of aspirated material may lead to obstruction of the respiratory tract.
- Bacterial infection: infection of the lower airways may lead to empyema, lung abscess, acute respiratory failure and acute lung injury. Persistent aspiration pneumonia is often due to anaerobes and it may progress to lung abscess or even bronchiectasis.
The usual site for an aspiration pneumonia is the apical and posterior segments of the lower lobe of the right lung. If the patient is supine then the aspirated material may also enter the posterior segment of the upper lobes.
- It is common and may account for up to 15% of patients with community-acquired pneumonia.
- Aspiration pneumonia is relatively common in hospital and usually involves infection with multiple bacteria, including anaerobes.
- It is more common in men, young children and the elderly.
Pathogens of community-acquired aspiration pneumonia are often the normal flora of the oropharynx including:
- Streptococcus pneumoniae
- Staphylococcus aureus
- Haemophilus influenzae
- Anaerobes - eg, Peptostreptococcus, Fusobacterium and Prevotella spp.
- 'Streptococcus milleri' group
- Klebsiella pneumoniae - increasingly seen in alcoholics
Pathogens of nosocomial aspiration pneumonia include:
- Oral anaerobes - as above
- Gram-positive cocci - eg, Peptostreptococcus spp., Peptococcus spp.
- Gram-negative bacilli - eg, enterobacteria (Klebsiella pneumoniae, Escherichia coli, Enterobacter spp.), Pseudomonas aeruginosa
- Meticillin-resistant Staphylococcus aureus (MRSA)
Risk factors for aspiration pneumonia
In the absence of a tracheo-oesophageal fistula, significant aspiration usually occurs only during periods of impaired consciousness, with reflux oesophagitis with an oesophageal stricture, or in bulbar palsy.
- Impaired consciousness: drug or alcohol abuse, general anaesthesia, seizures, sedation, acute stroke, central nervous system lesions, head injury.
- Poor mobility, nil by mouth, increasing age, chronic obstructive pulmonary disease (COPD), male gender and increasing number of medications.
- Swallowing disorders: oesophageal stricture, dysphagia, stroke, bulbar palsy, pharyngeal disease (eg, malignancy), neuromuscular disorders (eg, multiple sclerosis).
- Other: tracheo-oesophageal fistula, ventilator-associated pneumonia, nasogastric feeding tube, periodontal disease, gastro-oesophageal reflux, post-gastrectomy, tracheostomy.
- Nonspecific symptoms - eg, fever, headache, nausea, vomiting, anorexia, myalgia, weight loss
- Pleuritic chest pain
- Purulent sputum
- Signs may include tachycardia, tachypnoea, decreased breath sounds and dullness to percussion over areas of consolidation, pleural friction rub
- Severe infection may lead to hypoxia and septic shock
Other causes of respiratory distress, including:
- Other causes of pneumonia
- Foreign body in respiratory tract
- Cardiovascular disease
- Blood count: neutrophil leukocytosis,
- Electrolytes and renal function: dehydration, electrolyte imbalance,
- Blood culture,
- Blood gases,
- Culture of sputum:
- In patients with bacterial aspiration pneumonia, this may show organisms normally resident in the pharynx.
- Right, middle and lower lung lobes are the most common sites.
- Aspiration when upright may cause bilateral lower lung infiltrates.
- Right upper lobe often shows consolidation in alcoholics who aspirate in the prone position.
- Lung CT and bronchoscopy are only very occasionally required.
- Mechanical obstruction: removal of the object, normally by bronchoscopy.
- Tracheal suction if seen early.
- Intubation with positive pressure ventilation may be required.
- Bacterial infection of lower airways (the choice of antibiotics will be influenced by any recent previous antibiotic treatment, microbiology culture results and the patient's condition):
- Initial empirical antibiotic therapy while awaiting culture results.
- Antimicrobial therapy should be based on the patient's characteristics, the setting in which aspiration occurred, the severity of pneumonia, and available information regarding local pathogens and resistance patterns.
- Community-acquired aspiration pneumonia is often initially treated with co-amoxiclav. Metronidazole may need to be added if there is evidence of complications - eg, lung abscess. See the separate article Pneumonia for indications for hospital admission.
- Hospital-acquired aspiration pneumonia: a suitable combination in patients who have already recently been treated with antibiotics is piperacillin with tazobactam.
- The role of steroids is uncertain and not of proven benefit.
- Supportive therapy with fluid management, bronchodilators, and physiotherapy may help.
- Referral to speech and language therapists.
- Untreated, bacterial aspiration pneumonia may progress to lung abscess or bronchiectasis.
- Acute respiratory distress.
This depends on the underlying cause, general well-being of the patient, presence of complications, speed of diagnosis and effective treatment.
- Keep the head of the bed at a 30° angle: this reduces the risk or aspiration pneumonia in those at risk.
- Nasogastric feeding for at-risk patients - eg, poor gag reflex, dysphagia.
Further reading & references
- Kwong JC, Howden BP, Charles PG; New aspirations: the debate on aspiration pneumonia treatment guidelines. Med J Aust. 2011 Oct 3;195(7):380-1.
- Hibberd J, Fraser J, Chapman C, et al; Can we use influencing factors to predict aspiration pneumonia in the United Kingdom? Multidiscip Respir Med. 2013 Jun 11;8(1):39.
- Gomes GF, Pisani JC, Macedo ED, et al; The nasogastric feeding tube as a risk factor for aspiration and aspiration pneumonia. Curr Opin Clin Nutr Metab Care. 2003 May;6(3):327-33.
- DeLegge MH; Aspiration pneumonia: incidence, mortality, and at-risk populations. JPEN J Parenter Enteral Nutr. 2002 Nov-Dec;26(6 Suppl):S19-24; discussion
- Johnson JL, Hirsch CS; Aspiration pneumonia. Recognizing and managing a potentially growing disorder. Postgrad Med. 2003 Mar;113(3):99-102, 105-6, 111-2.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
|Original Author: Dr Colin Tidy||Current Version: Dr Gurvinder Rull||Peer Reviewer: Dr Adrian Bonsall|
|Last Checked: 07/07/2013||Document ID: 2625 Version: 25||© EMIS|