What’s new in ARDS (clinical studies)

Excerpt

The definition of the acute respiratory distress syndrome (ARDS) has been revised using a conceptual model of acute, diffuse, inflammatory lung injury, leading to increased pulmonary vascular permeability and lung weight, and loss of aerated lung tissue. The definition, however, was primarily based on feasibility, reliability, and validity [1]. The term “acute lung injury (ALI)” has been removed and ARDS is now categorized into mild, moderate, and severe, based on the degree of hypoxemia (P/F ratio) with a positive end-expiratory pressure (PEEP) of at least 5 cmH₂O. The accuracy of the new criteria has been evaluated from autopsy in 352 patients who met clinical criteria for ARDS at time of death, by specifically looking for the presence of diffuse alveolar damage (DAD). Sensitivity and specificity of the new criteria were 89 and 63 %, respectively, and DAD was significantly related to ARDS severity [2]. A prospective study in ten ICUs in France failed to validate the new definition, since neither the stratification by severity nor the P/F ratio at baseline was associated with 28-day mortality [3]. In this study, like in others, however, the numbers studied were relatively small for testing the predictive validity. In addition, the primarily goal of the definition is not to predict mortality at an individual level. The optimal timing of P/F ratio determination to diagnose ARDS is also still debated. A prospective, multicenter study in Spain found that using P/F ratio at 24 h with standard ventilatory setting (PEEP ≥ 10 cmH₂O and FiO₂ ≥ 0.5) had the best correlation to ICU mortality [4]. Costa et al. [5] also suggested that P/F ratio after 24 h could be more representative of severity and outcome of ARDS than using P/F ratio at baseline. The major problem with requiring a 24-h delay for the definition, discussed by the task force of the Berlin definition, is the risk of an additional delay for enrollment into trials. …