Elsevier

Journal of Critical Care

Volume 30, Issue 1, February 2015, Pages 40-48
Journal of Critical Care

Mechanical Ventilation
Aspiration pneumonia: A review of modern trends

https://doi.org/10.1016/j.jcrc.2014.07.011Get rights and content

Abstract

Purpose

The purpose was to describe aspiration pneumonia in the context of other lung infections and aspiration syndromes and to distinguish between the main scenarios commonly implied when the terms aspiration or aspiration pneumonia are used. Finally, we aim to summarize current evidence surrounding the diagnosis, microbiology, treatment, risks, and prevention of aspiration pneumonia.

Materials and methods

Medline was searched from inception to November 2013. All descriptive or experimental studies that added to the understanding of aspiration pneumonia were reviewed. All studies that provided insight into the clinical aspiration syndromes, historical context, diagnosis, microbiology, risk factors, prevention, and treatment were summarized within the text.

Results

Despite the original teaching, aspiration pneumonia is difficult to distinguish from other pneumonia syndromes. The microbiology of pneumonia after a macroaspiration has changed over the last 60 years from an anaerobic infection to one of aerobic and nosocomial bacteria. Successful antibiotic therapy has been achieved with several antibiotics. Various risks for aspiration have been described leading to several proposed preventative measures.

Conclusions

Aspiration pneumonia is a disease with a distinct pathophysiology. In the modern era, aspiration pneumonia is rarely solely an anaerobic infection. Antibiotic treatment is largely dependent on the clinical scenario. Several measures may help prevent aspiration pneumonia.

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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