TABLE 1.

Patient eligibility criteria for enrolment in studies contributing to CHARTER‐MT

Inclusion criteria	Age 18 years or older
	Currently in an intensive care unit (ICU) or scheduled for transfer to the ICU. During the pandemic, critically ill inpatients might be cared for outside of the walls of the usual physical environment of ICU. For this reason, ICU is defined as an area designated for inpatient care of the critically ill where therapies including invasive mechanical ventilation can be provided.
	Endotracheal tube in place.
	Intubated less than 2 days prior to randomisation.
	PaO2 to FiO2 ratio less than or equal to 300 while intubated.
	There is a PCR‐positive sample for SARS‐CoV‐2 within the past 21 days. The sample can be a nasal or pharyngeal swab, sputum, tracheal aspirate, bronchoalveolar lavage, or another sample from the patient.
Exclusion criteria	Heparin allergy or heparin‐induced thrombocytopaenia.
	APTT > 120 seconds, not due to anticoagulant therapy and does not correct with administration of fresh frozen plasma.
	Platelet count < 20 × 109 per L.
	Pulmonary bleeding or uncontrolled bleeding.
	Pregnant or might be pregnant.
	Acute brain injury that may result in long‐term disability.
	Myopathy, spinal cord injury, or nerve injury or disease with a likely prolonged incapacity to breathe independently, e.g. Guillain‐Barre syndrome.
	Death is imminent or inevitable within 24 hours.
	Clinician objection.
	Refusal of participant (person responsible) consent.

PCR, polymerase chain reaction; SARS‐CoV‐2, severe acute respiratory syndrome coronavirus 2; APTT, activated partial thromboplastin time; ICU, intensive care unit.