inclusion criteria: * age 18 years or older; * positive reverse-transcriptase-polymerase-chain-reaction (rt-pcr) assay for covid-19 in a respiratory tract sample; * intubated and mechanically ventilated; * acute onset of ards, as defined by berlin criteria as moderate-to-severe ards,3 which includes: (i) having pneumonia or worsening respiratory symptoms, (ii) bilateral pulmonary infiltrates on chest imaging (x-ray or ct scan), (iii) absence of left atrial hypertension, pulmonary capillary wedge pressure \<18 mmhg, or no clinical signs of left heart failure, and (iv) hypoxemia, as defined by a pao2/fio2 ratio of ≤200 mmhg on positive end-expiratory pressure (peep) of ≥5 cmh2o, regardless of fio2.

inclusion criteria: * age 18 years or older; * positive reverse-transcriptase-polymerase-chain-reaction (rt-pcr) assay for covid-19 in a respiratory tract sample; * intubated and mechanically ventilated; * acute onset of ards, as defined by berlin criteria as moderate-to-severe ards,3 which includes: (i) having pneumonia or worsening respiratory symptoms, (ii) bilateral pulmonary infiltrates on chest imaging (x-ray or ct scan), (iii) absence of left atrial hypertension, pulmonary capillary wedge pressure \<18 mmhg, or no clinical signs of left heart failure, and (iv) hypoxemia, as defined by a pao2/fio2 ratio of ≤200 mmhg on positive end-expiratory pressure (peep) of ≥5 cmh2o, regardless of fio2.

inclusion criteria: - age 18 years or older; - positive reverse-transcriptase-polymerase-chain-reaction (rt-pcr) assay for covid-19 in a respiratory tract sample; - intubated and mechanically ventilated; - acute onset of ards, as defined by berlin criteria as moderate-to-severe ards,3 which includes: (i) having pneumonia or worsening respiratory symptoms, (ii) bilateral pulmonary infiltrates on chest imaging (x-ray or ct scan), (iii) absence of left atrial hypertension, pulmonary capillary wedge pressure <18 mmhg, or no clinical signs of left heart failure, and (iv) hypoxemia, as defined by a pao2/fio2 ratio of ≤200 mmhg on positive end-expiratory pressure (peep) of ≥5 cmh2o, regardless of fio2.

inclusion criteria: - age 18 years or older; - positive reverse-transcriptase-polymerase-chain-reaction (rt-pcr) assay for covid-19 in a respiratory tract sample; - intubated and mechanically ventilated; - acute onset of ards, as defined by berlin criteria as moderate-to-severe ards,3 which includes: (i) having pneumonia or worsening respiratory symptoms, (ii) bilateral pulmonary infiltrates on chest imaging (x-ray or ct scan), (iii) absence of left atrial hypertension, pulmonary capillary wedge pressure <18 mmhg, or no clinical signs of left heart failure, and (iv) hypoxemia, as defined by a pao2/fio2 ratio of ≤200 mmhg on positive end-expiratory pressure (peep) of ≥5 cmh2o, regardless of fio2.