Factors associated with adherence to low-tidal volume strategy for acute lung injury and acute respiratory distress syndrome and their impacts on outcomes: an observational study and propensity analysis

Background. The purpose of this study was to investigate the factors affecting adherence to the low-tidal volume (LTV) strategy in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) and their impacts on outcomes. Methods. This prospective observational study included 111 patients with ALI/ARDS admitted to six intensive care units between March 2010 and February 2011. The patients were divided into the LTV group, which received a TV <= 7.5 mL/kg predicted body weight (PBW), and the non-LTV group, which received a TV >7.5 mL/kg PBW. We studied the association of selected clinical factors and adherence to the LTV strategy, and evaluated their impacts on 28-day mortality and 1-year mortality by the propensity-match process. Results. Adherence to the LTV strategy was only 44%, which was related to lung injury severity (odds ratio [OR]: 3.15, P=0.038), muscle relaxant use (OR: 3.28, P=0.031), and depth of sedation (OR: 0.65, P=0.008). Propensity score-based analysis showed that the LTV group had modestly better 28-day survival (P=0.081) and 1-year survival (P=0.067) than the non-LTV group. Moreover, muscle relaxant use was strongly associated with reducing the risk of death at both 28 days (hazard ratio [HR]: 0.122, 95% confidence interval [CI]: 0.027-0.542, P=0.006) and 1 year ([HR]: 0.111, 95% [CI]: 0.030-0.408, P=0.001). Conclusion. Adherence to the LTV strategy was strongly associated with the lung injury score, muscle relaxant use, and depth of sedation. Propensity score-based analysis showed that the use of LTV ventilation and muscle relaxants reduced 28-day and 1-year mortality in ALI/ARDS patients.