Ventilator-associated pneumonia: pathobiological heterogeneity and diagnostic challenges

Abstract

Ventilator-associated pneumonia (VAP) affects up to 20% of critically ill patients and induces significant antibiotic prescription pressure, accounting for half of all antibiotic use in the ICU. VAP significantly increases hospital length of stay and healthcare costs yet is also associated with long-term morbidity and mortality. The diagnosis of VAP continues to present challenges and pitfalls for the currently available clinical, radiological and microbiological diagnostic armamentarium. Biomarkers and artificial intelligence offer an innovative potential direction for ongoing future research. In this Review, we summarise the pathobiological heterogeneity and diagnostic challenges associated with VAP.

Fig. 1. Mechanisms of ventilator-acquired pneumonia.

1 External factors associated with ICU therapies include mechanical ventilation, sedation and paralysis agents and semi-recumbent positioning; 2 Endotracheal tube prevents glottis closure and provides direct communication to the lungs, allowing microaspiration of secretions from the nasal sinuses and oropharynx. The endotracheal cuff is at risk of deflation, movement and small folds, allowing pooled secretions to leak. A bacterial biofilm can form around the endotracheal tube, which can then become dislodged by movement or suctioning; 3 In response to invading pathogens, alveolar macrophages and neutrophils’ immune and inflammatory response lead to inflamed, oedematous and infected alveoli. Abbreviations: ICU = intensive care unit; AM = alveolar macrophages. Figure 1 was created with BioRender.com released under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International license (https://creativecommons.org/licences/by-nc-nd/4.0/deed.en).

Fig. 2. A simple, pragmatic ventilator-acquired pneumonia (VAP) diagnostic algorithm.

An algorithm for the diagnosis of VAP has been outlined; firstly, using clinical symptoms and features of infection and respiratory deterioration to inform initial suspicion in ventilated patients and to prompt completion of the Clinical Pulmonary Infection Score (CPIS). If uncertainty remains regarding the diagnosis of VAP due to missing data from the CPIS, clinicians are then prompted to complete sputum sampling and chest imaging using available methods to determine diagnosis. Antibiotic therapy is recommended on confirmed diagnosis of VAP.