Ventilator-associated pneumonia (VAP) is an infection frequently caused by Pseudomonas aeruginosa, Haemophilus spp. and Klebsiella spp. or by Staphylococcus aureus. Anaerobes are a rare cause of VAP. Virus or fungi are extremely infrequent in immunocompetent patients.
The physical placement of the endotracheal tube is the most important risk factor for the colonisation of oropharyngeal secretions and establishment of VAP. Aspiration of oropharyngeal secretions or leakage of bacteria around the endotracheal cuff is the major route of access by bacteria to the lower respiratory tract. Infected biofilms on the endotracheal tube can work as a reservoir of pathogens that can eventually trigger an episode of VAP.
Patients with late onset of VAP and prior exposure to antibiotics have a greater risk of being infected by a multidrug- resistant pathogen, such as P. aeruginosa, methicillin-resistant S. aureus or Acinetobacter baumanii.
Although the reaction to the infection is not homogeneous, in critically ill patients the mechanical, humoral and cellular responses are suboptimum, which means another challenge in the research and treatment of this disease.