COVID-19(21) Treatment(18) Patient(18) COVID-19 patient(16) Mortality(15) Critically ill(14) acute respiratory distress syndrome(13) therapy(12) significantly(11) Respiratory distress syndrome(10) respiratory distress(10) IL-6(9) acute respiratory distress(9) ARDS(9) extracorporeal membrane oxygenation(9) Coronavirus disease 2019(8) interleukin-6(8) coronavirus(8) coronavirus disease(8) intensive care(8) Cytosorb(8) outcome(8) ECMO(8) Severe case(7) in-hospital mortality(7) analyzed(7) retrospective(7) critically ill COVID-19 patients(7) median(7) treated(7)