Australian Prescriber Vol. 26 No. 1 2003 Aspiration pneumonia and pneumonitis Simon O’Connor, Chest Physician, Tamworth, New South Wales SYNOPSIS Epidemiology The two major aspiration syndromes are bacterial Table1 lists common causes of aspiration. Patients with stroke pneumonia and chemical pneumonitis. They have distinct or a critical illness requiring intensive care usually have features but may overlap. For chemical pneumonitis, several of these risk factors and make up a large proportion of supportive care is the mainstay of treatment while bacterial cases. Poor dental hygiene, especially in elderly or debilitated infection requires antibiotics. The choice of antibiotic is patients, results in colonisation of the mouth with potentially confused by conflicting evidence about the organisms pathogenic organisms and/or increased bacterial load. This responsible for infection, the poor yield from cultures in increases the risk of infection should aspiration occur. clinical practice and the lack of data comparing antibiotic regimens. Preventive strategies may help to reduce Clinical features aspiration in vulnerable patients. The history, examination and chest X-ray help to differentiate Index words: respiratory tract infection, antibiotics, between pneumonia and pneumonitis. corticosteroids. Aspiration pneumonia (Aust Prescr 2003;26:14–7) The clinical features are often indistinguishable from other causes of pneumonia, for example cough, chest pain, dyspnoea, Introduction fever and consolidation on chest X-ray. The presence of aspiration may be obvious, for example patients with motor Aspiration of oropharyngeal or gastric contents is a common, but often unrecognised cause of pneumonia. Focusing the Table 1 management of pneumonia on the distinction between community- and hospital-acquired disease means that Conditions that predispose to aspiration clinicians may not appreciate that aspiration can be a significant Altered level of consciousness factor in both presentations. • stroke • seizures Classification • intoxication (alcohol and other drugs) Aspiration can occur in healthy individuals without sequelae. • head trauma • anaesthesia The development of infection depends on other factors such as the size of the inoculum, virulence of the organisms and the Mechanical disruption of usual defences state of host defences such as glottic closure, cough reflex and • nasogastric tube • endotracheal intubation immune status. Pneumonia may arise following ‘micro’ • tracheostomy aspiration of virulent micro-organisms. However, the term • upper gastrointestinal endoscopy aspiration pneumonia is reserved for pneumonia arising when • bronchoscopy the size of the inoculum is large and/or host defences fail. Neuromuscular disease Aspiration can be divided into two broad categories. This has • multiple sclerosis important management implications. Aspiration of • Parkinson’s disease oropharyngeal contents, for example due to swallowing • myasthenia gravis difficulty, will cause bacterial pneumonia with mouth • bulbar or pseudobulbar palsy organisms predominating. Aspiration of gastric contents will Gastro-oesophageal disorders cause a chemical pneumonitis (e.g. Mendelson’s syndrome) • incompetent cardiac sphincter because the gastric contents are usually sterile, but their • oesophageal stricture acidity results in the rapid development of inflammation in the • neoplasm lungs. There may be overlap between pneumonia and • gastric outlet obstruction pneumonitis, but it is usually possible to make the distinction • protracted vomiting and tailor treatment accordingly. Other Other aspiration syndromes include airway obstruction due to • recumbent position a foreign body and exogenous lipoid pneumonia. • general debility 14 Australian Prescriber Vol. 26 No. 1 2003 neurone disease who cough when swallowing. However, usually obtained late in the course of the illness after aspiration is usually not witnessed and detecting it requires a complications such as empyema or lung abscess had developed. high degree of suspicion. Some patients will have a relatively Many of the patients were alcoholics and had foul sputum. sudden onset typical of infection with common organisms They presumably represent only part of the spectrum of such as Streptococcus pneumoniae . However, compared with aspiration pneumonia. The studies that isolated aerobic bacteria other causes of pneumonia, aspiration pneumonia tends to were performed at an earlier stage of the illness, usually before have a more indolent course, evolving over days to weeks antibiotics were used, and were taken from a wider range of rather than hours. Patients may present with late complications patients with aspiration pneumonia. such as weight loss, anaemia, lung abscess or empyema. Identifying organism(s) responsible for pneumonia is often Chest X-ray usually shows consolidation in the lung segments attempted but not achieved in clinical practice for a number of which were dependent at the time of aspiration. If the patient reasons. These include contamination of sputum specimens was supine the posterior segments of upper or apical segments with oropharyngeal flora, previous treatment with antibiotics of lower lobes are involved. The basal segments of lower lobes and the difficulties using invasive techniques (such as are involved if the patient was upright. The subsequent course bronchoscopy, transtracheal and transthoracic and pleural on X-ray is similar to pneumonia from other causes. Without aspiration) that are more reliable at isolating pathogens. treatment, patients have a higher incidence of cavitation and Anaerobic pathogens are difficult to identify even with good abscess formation. laboratory expertise. Aspiration of gastric contents Management In contrast to the aspiration of oropharyngeal secretions, All patients need supportive care 2 as well as specific treatment. aspiration of gastric contents is more likely to be witnessed or inferred. The original description of Mendelson’s syndrome Aspiration (chemical) pneumonitis involved obstetric patients undergoing ether anaesthesia. The airway should be cleared of fluids and particulate matter Witnessed aspiration was followed by respiratory distress and as soon as possible after the aspiration of gastric contents is cyanosis within two hours. The women’s X-rays showed witnessed. Endotracheal intubation should be considered for infiltrates in one or both lower lobes. Despite the severity of those who are unable to protect their airway. Although it is the illness, all the patients had recovered within 36 hours and common practice, there is no evidence that prophylactic use of there was radiographic resolution within seven days. antibiotics improves outcomes and, theoretically, this may Subsequent studies of aspiration pneumonitis have shown a make things worse by selecting out resistant organisms. more fulminant clinical course resulting in the adult respiratory Conversely, there may be difficulty distinguishing between distress syndrome. The different clinical course probably purely chemical pneumonitis and bacterial infection. In clinical reflects different study populations. The original patients studies, up to 25% of patients develop superimposed bacterial were young, previously healthy women, while later studies infection during the course of chemical pneumonitis. often involved elderly, debilitated patients or those burdened A reasonable compromise is to withhold antibiotics where the with serious comorbid conditions. diagnosis is clear. Empirical antibiotic treatment should be considered if there is no improvement after 48 hours. If the Microbiology pneumonitis cannot be distinguished from bacterial pneumonia There is conflicting information about the range of organisms or if patients have conditions known to be associated with responsible for aspiration pneumonia. The role of anaerobic colonisation of gastric contents (for example small bowel organisms from the mouth seemed to be established in the obstruction, or being in intensive care) immediate empirical 1970s and 80s using transtracheal and pleural aspiration to antibiotic treatment is appropriate. obtain specimens from the lower respiratory tract, avoiding Corticosteroids have been used, with varying degrees of the problem of contamination of expectorated sputum by enthusiasm, for decades in the management of aspiration normal mouth flora. The organisms include pneumonitis, but there are limited data to support this practice. Peptostreptococcus, Fusobacterium and Bacteroides . Studies in humans are generally unsuccessful and sometimes The use of protected brush specimens obtained via a the outcomes are worse for those treated with corticosteroids. bronchoscope in more recent times has yielded a different Large randomised controlled trials of high dose corticosteroids range of organisms, the identity of which depends on where for adult respiratory distress syndrome (of which chemical the infection is acquired. Streptococcus pneumoniae pneumonitis is a subset) showed no benefit. 3 As a result, this predominates in community-acquired cases, Staphylococcus treatment is not recommended. aureus and Gram negative organisms predominate in hospital- Bacterial aspiration pneumonia acquired cases. Anaerobic organisms have been conspicuously In contrast to chemical pneumonitis, antibiotics are the most 1 absent in these series. important component in the treatment of aspiration pneumonia. There are a number of reasons for these contradictory results. Early empirical treatment is required