Pulmonary Interstitial Emphysema (Macklin Effect), Quantitative Imaging Analysis and CytoKine Profiling to Predict Lung Frailty IN ARDS

Barotrauma occurs frequently in acute respiratory distress syndrome (ARDS), and has a difficult, non-standardized management. Unfortunately, mortality rates remain high (> 60% in COVID-19 ARDS, around 46% in non-COVID-19 ARDS). Interestingly, data from COVID-19 patients suggested that barotrauma may occur also in spontaneously breathing patients with ARDS. Accordingly, frailty of lung parenchyma represents a major issue in ARDS. Protective mechanical ventilation (i.e. ventilation with low tidal volume and low airway pressures) remains a cornerstone of supportive management of ARDS. Unfortunately, mechanical ventilation may worsen pulmonary damage (ventilator-induced lung injury) and, in high-risk patients, may induce barotrauma even when ventilator settings are maintained within the "safe" limit of protective ARDS. Early identification of high-risk features could therefore allow clinicians to individualize management of high-risk patients, by tailoring respiratory support and potentially select candidates for advanced support (i.e. extracorporeal membrane oxygenation) before development of overt barotrauma.

Macklin effect is a well-described radiological sign originally intended to differentiate between "peripheral" (distal airway rupture, "respiratory" barotrauma) and "central" (lesion to large airways/esophaegal injury) causes of air leakage in the mediastinum. However, the Investigators recently identified Macklin effect as a strong radiological predictor of barotrauma development in mechanically ventilated COVID-19 ARDS patients (sensitivity: 89.2%; specificity: 95.6%). In our cohort, radiologically-detected Macklin effect was identified 8-12 days before development of pneumomediastinum/pneumothorax. These preliminary results have been confirmed in a subsequent multicenter study (sample size 697 patients; sensitivity: 100%; specificity: 99.8%).

Furthermore, preliminary data suggest that early application of awake veno/venous extracorporeal membrane oxygenation (ECMO) before invasive mechanical ventilation in COVID-19 patients with severe ARDS and at high-risk for barotrauma (defined as presence of Macklin effect on chest CT imaging) might result in no barotrauma events with a low intubation rate.

Concurrently, a hyper inflammatory sub phenotype has been associated with overall worse outcome both in terms of mortality and ventilator-free days in ARDS. Moreover, the occurrence of lung injury during mechanical ventilation has been proven to be significantly related to the recruitment of mast cells via CXCL10/CXCR3 signaling .

In this view, confirmation of Macklin effect predictive role and identification of further, novel laboratory biomarkers could provide instruments for early risk stratification in ARDS patients.