Ventilator-Associated Pneumonia

The area of the alveolar epithelium of the lung is approximately 70 m(2). This area is constantly in contact with the ambient air and is therefore vulnerable to contamination with airborne microbes and particles of respirable size. Due to the configuration of the respiratory tract, airborne particles having diameters in the range of 0.5-2.0 μ can reach and deposit in the terminal part of the tracheobronchial tree - most bacteria are of this size. In reality, very few bacteria cause infections by spreading via the airborne route (e.g., mycobacteria, viruses, and legionella). Most bacteria cause pneumonia by first colonizing the upper respiratory tract and later descending into the tracheobronchial tree.