The definition of the acute respiratory distress syndrome (ARDS) was updated recently (1), with the new categories of ARDS severity providing better prognostic accuracy. However, the diagnostic criteria do not distinguish between different aetiologies of respiratory failure. Respiratory failure with physiological and radiological changes compatible with ARDS but where no common risk factors can be identified (ARDSCRF-) is an umbrella encompassing different pathological entities that should be characterised and managed separately (2). The importance of this differential diagnosis is potentially high, with the following implications:
- Inflammatory changes may be predominant in ARDSCRF- diseases, as opposed to diffuse alveolar disease (DAD), characterised by the presence of hyaline membranes;
- Widespread inflammation makes the lung more prone to ventilator induced lung injury (VILI), but could also potentially respond to steroids;
- Some of the ARDS mimickers, such as lung carcinomatosis and alveolar haemorrhage, have poor prognostic value.
In this large retrospective observational study (3) the authors examined the aetiology and outcomes of all ARDS patients admitted to two Parisian tertiary centres over a span of ten years (January 2003 – December 2012). 665 patients met the inclusion criteria, of which 7.5% (50 patients) had no identifiable CRF. The objectives of the study were two-fold:
- To identify the prevalence and aetiologies of ARDSCRF-, as well as to compare the ARDS CRF – and + patients in terms of presentation and outcomes;
- To evaluate the impact of potentially steroid-responsive lung changes on ICU outcome.
There were four aetiological categories of ARDSCRF- :
1. immune or associated with connective tissue disorders;
On the whole, ARDSCRF- patients had a longer course of disease before intensive care admission and mechanical ventilation, and a lower incidence of shock in the first 48 hours of ICU admission. Corticosteroids were more often prescribed in ARDSCRF- patients (84% vs 15%), and all ARDSCRF- survivors had steroid treatment. Notably, ARDSCRF- was associated with a two-fold increase in the likelihood of ICU death. Among the ARDSCRF-, a predominantly haemorrhagic or lymphocytic bronchoalveolar lavage and absence of radiological signs of fibrosis was associated with increased potentially reversibility and increased likelihood of ICU survival.
This study has a number of limitations, also acknowledged by the authors. However, it is an important work both from the clinical and the epidemiological perspective.
Take Home Message
ARDSCRF- may be more frequently encountered than expected and is associated with increased ICU mortality. However, some of these patients are responsive to steroids, with good clinical outcomes.
Review prepared by ESICM Journal Review Club member Oana Cole MD FRCA, Papworth Hospital, UK.
1. Ranieri VM, Rubenfeld GD, Thompson BT et al. Acute respiratory distress syndrome: the Berlin definition. JAMA 2012; 307: 2526 – 2533
2. Guerin C, Thompson T, Brower R. The ten diseases that look like ARDS. Intensive Care Med 2015; 41: 1099 – 1102
3. Gibelin A, Parrot A, Maitre B et al. Acute respiratory distress syndrome mimickers lacking common risk factors of the Berlin definition. Intensive Care Med 2016; 42: 164 – 172