Primary outcome: the primary outcome of the study will be the supplemental oxygen-free days (SOFDs) at 28 days.; defined as SOFDs = 28 - x; where x = number of days on which the patient is released from supplemental oxygen therapy after start.

Primary outcome: the primary outcome of the study will be the supplemental oxygen-free days (SOFDs) at 28 days.; defined as SOFDs = 28 - x; where x = number of days on which the patient is released from supplemental oxygen therapy after start.