Active_comparator: Awake prone positioning

The clinical intervention in the Intervention Group is Awake Prone Positioning, a standard therapy in intensive care units worldwide in ARDS care. The intervention should not be started later than 24 hours after randomization. An earlier start, as soon as possible, after randomization is strongly recommended. In patients in the intervention group standard Awake Prone Positioning for at least 10 hours/day for a length of 72 hours should be applied. The reach the targeted 10 hours / day (per 24 hours), it is strongly recommended to use blocks of a longer time period (e.g. multiple 3-5 hours blocks) within the 24h period to reach the anticipated APP goal. It is recommended that the APP therapy within the targeted intervention for 10 hours/day (per 24 h period) is not interrupted for more than 2 hours till reaching the goal of 10 hours/day (per 24h). It is further strongly recommended that one APP session should last at least 3 hours. (...) For more information please see the protocol.

No_intervention: Standard supine/semi-recumbent positioning

Patients randomized to the control arm will receive standard positioning at the discretion of the treating team but excluding APP. Control group patients will remain in their natural choice of position, which is anticipated to favour a supine, semi-recumbent position. The use of awake prone positioning as a so-called rescue intervention is discouraged in the control group and recorded as a protocol violation.~If patients have to be tracheal intubated and mechanically ventilated treatment should follow current ARDS guidelines. This includes PP in patients with mild to severe ARDS if PaO2/FiO2 is below 150 mmHg.