Ventilator-associated pneumonia in ARDS patients: the impact of prone positioning. A secondary analysis of the PROSEVA trial

Background The goal of this study was to assess the impact of prone positioning on the incidence of ventilator-associated pneumonia (VAP) and the role of VAP in mortality in a recent multicenter trial performed on patients with severe ARDS. Methods An ancillary study of a prospective multicenter randomized controlled trial on early prone positioning in patients with severe ARDS. In suspected cases of VAP the diagnosis was based on positive quantitative cultures of bronchoalveolar lavage fluid or tracheal aspirate at the 10 4 and 10 7 CFU/ml thresholds, respectively. The VAP cases were then subject to central, independent adjudication. The cumulative probabilities of VAP were estimated in each position group using the Aalen–Johansen estimator and compared using Gray’s test. A univariate and a multivariate Cox model was performed to assess the impact of VAP, used as a time-dependent covariate for mortality hazard during the ICU stay. Results In the supine and prone position groups, the incidence rate for VAP was 1.18 (0.86–1.60) and 1.54 (1.15–2.02) per 100 days of invasive mechanical ventilation ( p = 0.10), respectively. The cumulative probability of VAP at 90 days was estimated at 46.5 % (27–66) in the prone group and at 33.5 % (23–44) in the supine group. The difference between the two cumulative probability curves was not statistically significant ( p = 0.11). In the univariate Cox model, VAP was associated with an increase in the mortality rate during the ICU stay [HR 1.65 (1.05–2.61), p = 0.03]. HR increased to 2.2 (1.39–3.52) ( p