Introduction
Definition of ARDS
Timing
| Within 1 week of a known clinical insult or new or worsening respiratory symptoms | |
---|---|---|
Chest imaging (chest radiograph or computed tomography scan)
| Bilateral opacities; not fully explained by effusions, lobar/lung collapse, or nodules | |
Origin of edema
| Respiratory failure not fully explained by cardiac failure or fluid overload Need objective assessment (e.g., echocardiography) to exclude hydrostatic edema if no risk factor present | |
Oxygenation
| Mild | 200 mmHg < PaO2/FIO2 ≤ 300 mmHg with PEEP or CPAP ≥5 cmH2O |
Moderate | 100 mmHg < PaO2/FIO2 ≤ 200 mmHg with PEEP ≥5 cmH2O | |
Severe | PaO2/FIO2 ≤ 100 mmHg with PEEP ≥5 cmH2O |
Epidemiology of ARDS
Aetiology of ARDS
Direct lung injury
|
Indirect lung injury
|
---|---|
Pneumonia | Sepsis |
Aspiration of gastric contents | Multiple trauma |
Pulmonary contusion | Cardiopulmonary bypass |
Near drowning | Acute pancreatitis |
Inhalation injury | Drug overdose |
Reperfusion pulmonary edema | Transfusion of blood products |
Pathology
Early and late phases of lung injury
Biomarkers
Epithelial markers
-
RAGE is highly expressed in lung epithelium [24], and especially expressed on alveolar type 1 epithelial cells [25]. The use as a marker has been questionable but some studies have shown higher levels of RAGE were associated with impaired alveolar fluid clearance in patients with ARDS hence the severity of lung epithelial injury [26]. RAGE plasma levels in patients with severe ARDS correlated with mortality in patients ventilated with high tidal volumes [27]. In a meta-analysis sRAGE was found to be useful in ARDS diagnosis in a high risk population, but not associated with mortality [21], although other studies have shown no association [28, 29].
Endothelial markers
Inflammatory cytokines
Coagulation and fibrinolysis
Combinations of biomarkers
Blood biomarkers of ARDS: Calfee group, SF
Septic shock biomarkers: ProCESS study
Influenza ARDS: MOSAIC
Metabolomics
Transcriptomics – Gene expression mRNA
MicroRNA (MiRNA)
Genetics (DNA)
Therapies
Supportive therapy | Comment |
---|---|
Lung protective ventilation with low tidal volume (4–8 ml/kg predicted body weight) and low inspiratory pressures (plateau pressure < 30 cmH2O) | Strong recommendation [75] |
Higher level of PEEP§ in patients with moderate or severe ARDS | Conditional recommendation [75] |
Lung recruitment maneuvers in patients with moderate or severe ARDS | Conditional recommendation [75] |
Prone positioning for more than 12 h/die in patients with severe ARDS | Strong recommendation [75] |
HFOV | Strong recommendation against the routine use of HFOV [75] |
ECMO | Rescue therapy for refractory hypoxemia in severe ARDS. No recommendation is made, additional studies are needed [75]. |
Conservative fluid management strategy | |
Pharmacological therapy | |
Glucocorticoids | Inconclusive results on doses and duration of treatment. May provide some benefit on oxygenation, reduce inflammatory process and ventilation days. They are harmful if started 14 days after ARDS diagnosis [96]. |
Inhaled nitric oxide (NO) | Improves transiently oxygenation. Does not affect mortality. Higher grade of AKI [80]. |
Neuromuscolar blockade | Improve outcomes in patients with moderate to-severe ARDS, ensures patient–ventilator synchrony and reduces the risk of VILI [81]. Higher risk of diaphragm atrophy and ICU acquired weakness. Ongoing trial (NCT02509078). |
Mesenchimal stem cells | Phase 2a clinical trials to establish safety in ARDS are in progress and two phase 1 trials did not report any serious adverse events [81]. |