Pneumonia Pathogens With ALI or ARDS?
What are the most common pathogenic bacteria for acute severe pneumonia with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS)? What is the best way to identify them?
This is a very important question, particularly given that pneumonia is the most common cause of ALI/ARDS. Among all patients with ALI/ARDS, pneumonia accounts for approximately 40% of cases. Therefore, to some extent, treating ALI/ARDS very often involves treating pneumonia.
Causative organisms for pneumonia as a cause of ALI/ARDS are incompletely described. In part, this relates to changes in organisms during the course of hospitalization. As with pneumonia in general, the pathogens associated with community-acquired pneumonia are significantly different from those associated with healthcare-associated or ventilator-associated pneumonia. In addition, the causative organisms in ventilator-associated pneumonia differ depending on whether the onset was early in the course of ventilation or later (≥ 5 days). In particular, late-onset ventilator-associated pneumonia is associated with more resistant and Gram-negative organisms. Finally, specifically for patients with ALI/ARDS, the diagnosis of ventilator-associated pneumonia can be difficult both radiographically and microbiologically, due to existing radiographic abnormalities and endotracheal colonization.
The identification of causative organisms for pneumonia and subsequent ALI/ARDS is similarly driven by the likely type of pneumonia (community-acquired vs healthcare/ventilator-associated) and the duration of mechanical ventilation prior to the diagnosis. For patients with community-acquired pneumonia, the diagnosis can often be established by sputum culture or endotracheal aspirate. When this is not feasible or does not result in a suitable specimen, bronchoscopy may be performed to improve the yield, with the caveat that approximately 50% of pneumonia cases will never recover an organism. For patients who have undergone > 48 hours of hospitalization or mechanical ventilation, colonization of the respiratory tract may preclude an accurate microbiological diagnosis. For this reason, as with ventilator-associated pneumonia, bronchoscopically obtained specimens may be preferred. Within the realm of bronchoscopy, the type of collected specimen may also influence the accuracy (particularly the specificity) of the diagnosis: bronchial washings more closely relate to endotracheal aspirates, while bronchoalveolar lavage and protected specimen brush cultures tend to have less confounding by colonizing organisms.
What are the most common pathogenic bacteria for acute severe pneumonia with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS)? What is the best way to identify them?
This is a very important question, particularly given that pneumonia is the most common cause of ALI/ARDS. Among all patients with ALI/ARDS, pneumonia accounts for approximately 40% of cases. Therefore, to some extent, treating ALI/ARDS very often involves treating pneumonia.
Causative organisms for pneumonia as a cause of ALI/ARDS are incompletely described. In part, this relates to changes in organisms during the course of hospitalization. As with pneumonia in general, the pathogens associated with community-acquired pneumonia are significantly different from those associated with healthcare-associated or ventilator-associated pneumonia. In addition, the causative organisms in ventilator-associated pneumonia differ depending on whether the onset was early in the course of ventilation or later (≥ 5 days). In particular, late-onset ventilator-associated pneumonia is associated with more resistant and Gram-negative organisms. Finally, specifically for patients with ALI/ARDS, the diagnosis of ventilator-associated pneumonia can be difficult both radiographically and microbiologically, due to existing radiographic abnormalities and endotracheal colonization.
The identification of causative organisms for pneumonia and subsequent ALI/ARDS is similarly driven by the likely type of pneumonia (community-acquired vs healthcare/ventilator-associated) and the duration of mechanical ventilation prior to the diagnosis. For patients with community-acquired pneumonia, the diagnosis can often be established by sputum culture or endotracheal aspirate. When this is not feasible or does not result in a suitable specimen, bronchoscopy may be performed to improve the yield, with the caveat that approximately 50% of pneumonia cases will never recover an organism. For patients who have undergone > 48 hours of hospitalization or mechanical ventilation, colonization of the respiratory tract may preclude an accurate microbiological diagnosis. For this reason, as with ventilator-associated pneumonia, bronchoscopically obtained specimens may be preferred. Within the realm of bronchoscopy, the type of collected specimen may also influence the accuracy (particularly the specificity) of the diagnosis: bronchial washings more closely relate to endotracheal aspirates, while bronchoalveolar lavage and protected specimen brush cultures tend to have less confounding by colonizing organisms.
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