Within the categories described, the causes of nosocomial pneumonia also vary
considerably according to geographic, temporal, and intra-hospital factors. The use of up-to-
date local epidemiologic ICU data on endemic pathogens can help select the most appropriate
empirical antibiotic regimen and infection-control strategies.
Table 1 lists the conditions that may predispose a patient to acquire VAP attributable to a
specific pathogen.
RISK FACTORS
Several risk factors have been linked to nosocomial pneumonia through univariate and
multivariate analysis of prospective and retrospective data (12,26,67,81–92). The elderly and
moderately to severely ill are especially at risk. In these subjects, respiratory tract function is
impaired, lung volume is diminished, and airway clearance may be reduced. Trauma, surgery,
medications, and respiratory therapy devices may additionally impair the capacity of the lungs
to ward off infection.
Notwithstanding, the most significant risk factor for nosocomial pneumonia is mechan-
ical ventilation. In effect, the terms “nosocomial pneumonia” and “ventilator-associated
pneumonia” are often used interchangeably. It has been described that when an endotracheal
tube is introduced, many lines of host defense are bypassed, such that microorganisms gain
direct access to the lower respiratory tract (26,83,87,89). Further, as the tube is inserted,
possible damage to the tracheal mucosa will allow pathogens to achieve a foothold. Table 2
provides additional risk factors listed by category for both VAP and pneumonia occurring in
both ventilated and more mixed non-ventilated hospital populations.
The risk factors identified by Croce et al. (115) to predict VAP in a review of admissions
to a trauma center over a 28-month period were as follows: penetrating wounds, a high
Glasgow Coma Scale score, spinal cord injury, and the coexistence of emergent laparotomy, a
high Injury Severity Score, number of blood units transfused in the resuscitation room, and the
place of initial intubation.
PREVENTION
Understanding the pathogenesis of VAP (colonization of the aerodigestive tract with
pathogenic bacteria and their subsequent aspiration) has allowed the development of several
VAP-prevention strategies. These education-based programs have shown that the occurrence
of VAP can be reduced by as much as 50% or more (116) if measures that prevent colonization
Table 1 Risk Factors for VAP Attributable to a Specific Microorganism
Risk factor Responsible microorganism
Aspiration Anaerobic microorganisms
Abdominal surgery Anaerobic microorganisms
Coma S. aureus
Iv drug abuse
Diabetes mellitus
Chronic renal failure
Prolonged ICU or hospital stay Pseudomonas aeruginosa
Antimicrobial therapy Acinetobacterspp.
Stenotrophomonas maltophilia
Enterobacterspp.
Methicillin-resistantS. aureus
Chronic obstructive pulmonary
disease
Pseudomonas aeruginosaAge>65 years
Hypoalbuminemia<2.5 g/dL
Non-resolving pneumonia
Immunocompromise Candidaspp.
Isolated outbreaks Aspergillusspp.
Mucorspp.
182 Bouza and Burillo