Temporal nomenclature and definitions for prolonged course acute respiratory distress syndrome: a scoping review

Background
Acute respiratory distress syndrome (ARDS) affects over twenty percent of critically ill, mechanically ventilated patients and carries a high mortality rate. Prolonged course ARDS is associated with high healthcare costs and extended intensive care unit admission. It exhibits considerable heterogeneity in aetiology, biology, and chronology. ARDS criteria are subject to continuous revision by expert consensus. Expert consensus has not provided a clear definition of a prolonged course of ARDS (i.e., persistent or non-resolving).

Research Question
This review aimed to provide an overview of the nomenclature and definitions used to identify patients with a prolonged course of ARDS.

Study Design and Methods
We conducted a scoping review to assess the definitions used for prolonged course ARDS. PubMed and EMBASE databases were searched using a predefined and preregistered search string.

Results
We included 66 articles and found marked heterogeneity in nomenclature and definitions. Fifteen different nomenclatures were used with timeframes ranging from thirty minutes to several weeks. This heterogeneity persisted across periods of the existing consensus criteria (American–European Consensus Conference versus the Berlin definition) and research topics (i.e., pharmacology or biomarkers). The most common nomenclatures were persistent (n=26, 39%) and late (n=26, 39%), with the most frequent time definition being seven days after onset of ARDS (n=28, 42%).

Interpretation
The relative paucity of studies found using a comprehensive search strategy and the use of heterogeneous definitions preclude adequate meta-analyses required to gain insight into the aetiology, outcomes, and possible interventions aimed at improving patient care. A focused discussion is required to create a consensus definition for prolonged course ARDS to standardize research efforts towards improving patient outcomes.