Identification and validation of distinct biological phenotypes in patients with acute respiratory distress syndrome by cluster analysis.

RATIONALE: We hypothesised that patients with acute respiratory distress syndrome (ARDS) can be clustered based on concentrations of plasma biomarkers and that the thereby identified biological phenotypes are associated with mortality. METHODS: Consecutive patients with ARDS were included in this prospective observational cohort study. Cluster analysis of 20 biomarkers of inflammation, coagulation and endothelial activation provided the phenotypes in a training cohort, not taking any outcome data into account. Logistic regression with backward selection was used to select the most predictive biomarkers, and these predicted phenotypes were validated in a separate cohort. Multivariable logistic regression was used to quantify the independent association with mortality. RESULTS: Two phenotypes were identified in 454 patients, which we named 'uninflamed' (N=218) and 'reactive' (N=236). A selection of four biomarkers (interleukin-6, interferon gamma, angiopoietin 1/2 and plasminogen activator inhibitor-1) could be used to accurately predict the phenotype in the training cohort (area under the receiver operating characteristics curve: 0.98, 95% CI 0.97 to 0.99). Mortality rates were 15.6% and 36.4% (p<0.001) in the training cohort and 13.6% and 37.5% (p<0.001) in the validation cohort (N=207). The 'reactive phenotype' was independent from confounders associated with intensive care unit mortality (training cohort: OR 1.13, 95% CI 1.04 to 1.23; validation cohort: OR 1.18, 95% CI 1.06 to 1.31). CONCLUSIONS: Patients with ARDS can be clustered into two biological phenotypes, with different mortality rates. Four biomarkers can be used to predict the phenotype with high accuracy. The phenotypes were very similar to those found in cohorts derived from randomised controlled trials, and these results may improve patient selection for future clinical trials targeting host response in patients with ARDS.

Donor smoking is associated with pulmonary edema, inflammation and epithelial dysfunction in ex vivo human donor lungs.

Although recipients of donor lungs from smokers have worse clinical outcomes, the underlying mechanisms are unknown. We tested the association between donor smoking and the degree of pulmonary edema (as estimated by lung weight), the rate of alveolar fluid clearance (AFC; measured by airspace instillation of 5% albumin) and biomarkers of lung epithelial injury and inflammation (bronchoalveolar lavage [BAL] surfactant protein-D (SP-D) and IL-8) in ex vivo lungs recovered from 298 organ donors. The extent of pulmonary edema was higher in current smokers (n = 127) compared to nonsmokers (median 408 g, interquartile range [IQR] 364-500 vs. 385 g, IQR 340-460, p = 0.009). Oxygenation at study enrollment was worse in current smokers versus nonsmokers (median PaO2 /FiO2 214 mm Hg, IQR 126-323 vs. 266 mm Hg, IQR 154-370, p = 0.02). Current smokers with the highest exposure (≥20 pack years) had significantly lower rates of AFC, suggesting that the effects of cigarette smoke on alveolar epithelial fluid transport function may be dose related. BAL IL-8 was significantly higher in smokers while SP-D was lower. These findings indicate that chronic exposure to cigarette smoke has important effects on inflammation, gas exchange, lung epithelial function and lung fluid balance in the organ donor that could influence lung function in the lung transplant recipient.

Determining the aetiology of pulmonary oedema by the oedema fluid-to-plasma protein ratio.

We hypothesised that the oedema fluid-to-plasma protein (EF/PL) ratio, a noninvasive measure of alveolar capillary membrane permeability, can accurately determine the aetiology of acute pulmonary oedema. 390 mechanically ventilated patients with acute pulmonary oedema were enrolled. A clinical diagnosis of acute lung injury (ALI), cardiogenic pulmonary oedema or a mixed aetiology was based on expert medical record review at the end of hospitalisation. The EF/PL ratio was measured from pulmonary oedema fluid and plasma samples collected at intubation. 209 patients had a clinical diagnosis of ALI, 147 had a diagnosis of cardiogenic pulmonary oedema and 34 had a mixed aetiology. The EF/PL ratio had an area under the receiver-operating curve of 0.84 for differentiating ALI from cardiogenic pulmonary oedema. Using a predefined cut-off of 0.65, the EF/PL ratio had a sensitivity of 81% and a specificity of 81% for the diagnosis of ALI. An EF/PL ratio >/=0.65 was also associated with significantly higher mortality and fewer ventilator-free days. Noninvasive measurement of the EF/PL ratio is a safe and reliable bedside method for rapidly determining the aetiology of acute pulmonary oedema that can be used at the bedside in both developed and developing countries.

Plasma receptor for advanced glycation end products and clinical outcomes in acute lung injury.

OBJECTIVES: To determine whether baseline plasma levels of the receptor for advanced glycation end products (RAGE), a novel marker of alveolar type I cell injury, are associated with the severity and outcomes of acute lung injury, and whether plasma RAGE levels are affected by lower tidal volume ventilation. DESIGN, SETTING AND PARTICIPANTS: Measurement of plasma RAGE levels from 676 subjects enrolled in a large randomised controlled trial of lower tidal volume ventilation in acute lung injury. MEASUREMENTS AND MAIN RESULTS: Higher baseline plasma RAGE was associated with increased severity of lung injury. In addition, higher baseline RAGE was associated with increased mortality (OR for death 1.38 (95% CI 1.13 to 1.68) per 1 log increment in RAGE; p = 0.002) and fewer ventilator free and organ failure free days in patients randomised to higher tidal volumes. These associations persisted in multivariable models that adjusted for age, gender, severity of illness and the presence of sepsis or trauma. Plasma RAGE was not associated with outcomes in the lower tidal volume group (p = 0.09 for interaction in unadjusted analysis). In both tidal volume groups, plasma RAGE levels declined over the first 3 days; however, the decline was 15% greater in the lower tidal volume group (p = 0.02; 95% CI 2.4% to 25.0%). CONCLUSIONS: Baseline plasma RAGE levels are strongly associated with clinical outcomes in patients with acute lung injury ventilated with higher tidal volumes. Lower tidal volume ventilation may be beneficial in part by decreasing injury to the alveolar epithelium.