PRone positioN in Patients With spontanEous ventiLation and Acute Hypoxemic respIratory FailurE

The investigators intend to recruit acute hypoxemic respiratory failure patients with a respiratory rate of more than 25 breaths per minute, SpO2 \< 94% and FiO2 of at least 40% or more by either Venturi facemask, HFNC, or NIV/CPAP and, absence of decompensated respiratory acidosis during two years. Currently, the investigators expect about 35 centers to participate in the trial. Demographic data and clinical characteristics on screened patients, regardless of enrolment criteria match, will be recorded (registry). The investigators will randomize 650 patients admitted to the participating centers' intensive care units and expect each participating center to randomize at least 25 patients who meet all inclusion criteria.