Mechanical VentilationAspiration pneumonia: A review of modern trends
Section snippets
Common consequences of aspiration
It is important to understand that aspiration is a common event that may lie within the spectrum of normal physiology. A large proportion of healthy people with normal mental status aspirate during sleep based on the detection of radiolabeled oral dyes in the lungs of healthy volunteers [6], [7], [8]. The anesthesia literature began highlighting aspiration during ether anesthesia as early as 1950 based on case reports and animal studies carried out during the 19th century [9]. These reports
Clinical syndromes
Although occurring in otherwise healthy people, several important clinical consequences of aspiration can occur. The most clinically relevant are listed in Table 1. These various manifestations of aspiration can be distinguished by 3 main characteristics—whether the inoculum is infectious or not, the volume of the inoculum, and the acuity of onset of the clinical syndrome.
Many of the aspiration syndromes are a result of noninfectious microaspiration, often due to gastroesophogeal reflux disease
Risk factors for aspiration pneumonia
Specific predisposing factors for aspiration pneumonia focus on the risk for high frequency and/or large volume of aspiration. Some risks may be more pertinent for the macroaspiration characteristic of aspiration pneumonitis or anaerobic pleuropneumonia than for microaspiration. Additionally, factors that influence the resident bacterial flora leading to colonization by more virulent pathogens, which are more likely to overwhelm the normal protective mechanisms, also play a role in development
Diagnosis
Like all pneumonias, the diagnosis of aspiration pneumonia rests mostly on the history of presenting illness, medical history, vital signs, and chest radiograph. In clinical practice, aspiration pneumonia is most often coded as the diagnosis when a new chest radiograph infiltrate in a dependent pulmonary segment is found in patients with risk factors for aspiration. In a bed-bound patient, the dependent pulmonary segments are the posterior segments of the upper lobes and the superior segments
Microbiology
The unique pathophysiology of aspiration pneumonia may lend itself to unique pathogens. However, the microbiology, and therefore the treatment, has seen significant changes over the last 40 to 50 years.
The original teaching was that anaerobic bacteria were by far the most common pathogens in aspiration pneumonia based on well-done microbiology studies undertaken in patients with aspiration pneumonia acquired in and out of the hospital from the 1960s to 1980s. Bartlett and Gorbach [17], [92] and
Treatment
As one would expect, empirical treatment of aspiration pneumonia has evolved, given the above changes in the microbiology of the infection [102]. Intravenous penicillin was the drug of choice in the past, as anaerobes constituted the vast majority of infections with few penicillinase-producing bacterial strains [103], [104]. A randomized controlled trial (RCT) of 39 patients with lung abscesses compared penicillin with clindamycin in the early 1980s [105]. Although a small group of patients,
Prevention
Aspiration pneumonia can be a grave illness despite treatment, so prevention is important. Several randomized trials have been investigated to prevent aspiration pneumonia, but most are limited by enrollment.
Dietary interventions have been studied in patients with dysphagia. In a small study involving patients with dysphagia secondary to neurodegenerative disease (pseudobulbar dysphagia) [111], more aspiration pneumonia occurred in those on a pureed diet compared to a mechanical soft diet with
Conclusions
Aspiration pneumonia is a common clinical syndrome with a distinct pathophysiology. Aspiration pneumonia must be distinguished from other aspiration syndromes that include similar risk factors including abnormalities in the cough reflex, oral microbiology, and the swallow mechanism. Despite the traditional teaching, aspiration pneumonia is difficult to distinguish from other pneumonia syndromes and therefore shares many features with CAP and HAP. In the modern era, aspiration pneumonia warrants
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