Crit Care Med 2009; 37:2709-2718

To determine the attributable mortality of ventilator-associated pneumonia in a systematic review and meta-analysis of observational studies. Ventilator-associated pneumonia is generally believed to increase the mortality of patients. This notion is predominantly based on the results of observational studies.

Data source
We performed a systematic search strategy using PubMed, Web of Science, and Embase from their inception through February 2007. In addition, a reference and related article search was performed.

Study selection
Studies were included if they reported mortality rates of patients with and without ventilator-associated pneumonia.
Data extraction and synthesis
Fifty-two studies with a total of 17,347 patients met the inclusion criteria. Pooling of all studies resulted in relative risk of 1.27 (95% Confidence Interval = 1.15-1.39), but heterogeneity was considerable (I2 statistic = 69%). The origin of heterogeneity could not be explained by differences in study design, study quality, and diagnostic approach. However, heterogeneity was limited for studies investigating only trauma patients (I2 = 1.3%) or patients with acute respiratory distress syndrome (I2 = 0%), with estimated relative risk of 1.09 (95% Confidence Interval = 0.87-1.37) among trauma patients and 0.86 (95% Confidence Interval = 0.72-1.04) among patients with acute respiratory distress syndrome.

Conclusions
There is no evidence of attributable mortality due to ventilator-associated pneumonia in patients with trauma or acute respiratory distress syndrome. However, in other nonspecified patient groups, there is evidence for attributable mortality due to ventilator-associated pneumonia, but this could not be quantified due to heterogeneity in study results. More detailed studies, allowing subgroup analyses, are needed to determine the attributable mortality of ventilator-associated pneumonia in these patient populations.