Morbidity and Mortality

ARDS is one of the most severe pulmonary diseases, leading to significant patient morbidity and healthcare burden [7]. Thus, it is expected that any iatrogenic complication that ensues during the course of ARDS may delay weaning from the MV, prolong the intensive care unit (ICU) stay, require additional treatments, and exponentially increase costs. In a recent international, multicenter, prospective cohort study of 2377 patients with ARDS, the median length of MV was 8 days (interquartile range (IQR), 4-16). Early studies have consistently reported a significant increase in duration of MV, when VAP occurred in ARDS patients. Chastre et al. found that in ARDS patients who developed VAP, the length of MV increased from 17 ± 19 to 34 ± 32 days, whereas Markowicz et al. found that in ARDS patients, the first episode of VAP did not occur until a mean length of MV of 11.7 ± 11.9 days. Interestingly, the mean duration of MV, for ARDS patients who did not develop VAP, was highly similar: 11.3 ± 9.1 days. Conversely, when they did develop VAP, the length of stay increased up to 33 ± 21 days.

It is fascinating that in early studies [6, 8], investigators failed to demonstrate any impact of VAP on mortality. Considering the clinical severity of ARDS, it is somewhat difficult to justify the lack of effect on mortality, when VAP complicates the course of the disease. Yet, several factors may explain these counterintuitive findings. First, in ARDS patients, the occurrence of VAP can be biased by the presence of competing events, specifically death or ICU discharge, which preclude VAP occurrence or dramatically changing its risk [9]. For instance, a highly severe ARDS patient, at high risk of VAP, could decease during the time on MV, but before the onset of VAP. Unfortunately, traditional methods of time-to-event analysis considered patients who died while on MV as non-informative censoring, resulting in biased estimates. Yet, in more recent analyses [10-12], patients have been considered under risk either up to the occurrence of VAP or until one of the other competing events occurred or until follow-up was completed. Thus, latest studies [10], in patients without ARDS, reported an attributable mortality of 10%. Also, it seems that surgical patients and with midrange severity of illness present the highest associated risk of mortality. To the best of our knowledge, no studies have been specifically assessed the attributable mortality of VAP in ARDS patients. Nevertheless, considering the severity of this condition, it is rationale to assume that VAP might unhinge the delicate clinical balance of these patients, and lead to worse outcome.