Ventilator-associated pneumonia - Diagnosis, pathogenesis and prevention

Ventilator-associated pneumonia is common, difficult to diagnose, affects t he most vulnerable of patients and carries a high mortality. During prolong ed mechanical ventilation the oropharynx, sinuses, dentition and stomach of critically ill patients become colonised with pathogenic bacteria. Colonis ed secretions pool in the oropharynx and subglottic space. These secretions repeatedly gain access to the lower airways by leakage past the tracheal t ube cuff. If host defence mechanisms are overwhelmed, multiplication occurs in the lower respiratory tract producing an inflammatory response in the b ronchioles and alveoli. The inflammatory response is characterised by capil lary congestion, leucocyte and macrophage infiltration and fibrinous exudat ion into the alveolar spaces. If this inflammatory response occurs more tha n 48 h after intubation, it is called ventilator-associated pneumonia. Prev ention depends on reducing upper airway and gastrointestinal reservoirs of bacteria, reducing or abolishing aspiration of these bacteria past the trac heal tube cuff and enhancing bacterial clearance from the lower airways.