* pao2/fio2 ≤ 200 * respiratory rate ≥ 28 breaths/min and or severe dyspnea and or use of accessory muscles * need for immediate intubation or noninvasive ventilation (including cpap) according to clinical judgment (e.g. clinical diagnosis of cardiogenic pulmonary edema, respiratory acidosis ph ≤ 7.3) * patients already on cpap/niv or hfnt at study screening * septic shock * evidence of multiorgan failure * glasgow coma scale \< 13 * inability to comprehend the study content and give informed consent * paco2 \> 45 mmhg, (if blood gas available) or history of chronic hypercapnia * patient already on long-term oxygen therapy (ltot) or home niv/cpap (even if only overnight) * neuromuscular disease * limitation of care based on patients' or physicians' decision

* pao2/fio2 ≤ 200 * respiratory rate ≥ 28 breaths/min and or severe dyspnea and or use of accessory muscles * need for immediate intubation or noninvasive ventilation (including cpap) according to clinical judgment (e.g. clinical diagnosis of cardiogenic pulmonary edema, respiratory acidosis ph ≤ 7.3) * patients already on cpap/niv or hfnt at study screening * septic shock * evidence of multiorgan failure * glasgow coma scale \< 13 * inability to comprehend the study content and give informed consent * paco2 \> 45 mmhg, (if blood gas available) or history of chronic hypercapnia * patient already on long-term oxygen therapy (ltot) or home niv/cpap (even if only overnight) * neuromuscular disease * limitation of care based on patients' or physicians' decision

- pao2/fio2 ≤ 200 - respiratory rate ≥ 28 breaths/min and or severe dyspnea and or use of accessory muscles - need for immediate intubation or noninvasive ventilation (including cpap) according to clinical judgment (e.g. clinical diagnosis of cardiogenic pulmonary edema, respiratory acidosis ph ≤ 7.3) - patients already on cpap/niv or hfnt at study screening - septic shock - evidence of multiorgan failure - glasgow coma scale < 13 - inability to comprehend the study content and give informed consent - paco2 > 45 mmhg, (if blood gas available) or history of chronic hypercapnia - patient already on long-term oxygen therapy (ltot) or home niv/cpap (even if only overnight) - neuromuscular disease - limitation of care based on patients' or physicians' decision

- pao2/fio2 ≤ 200 - respiratory rate ≥ 28 breaths/min and or severe dyspnea and or use of accessory muscles - need for immediate intubation or noninvasive ventilation (including cpap) according to clinical judgment (e.g. clinical diagnosis of cardiogenic pulmonary edema, respiratory acidosis ph ≤ 7.3) - patients already on cpap/niv or hfnt at study screening - septic shock - evidence of multiorgan failure - glasgow coma scale < 13 - inability to comprehend the study content and give informed consent - paco2 > 45 mmhg, (if blood gas available) or history of chronic hypercapnia - patient already on long-term oxygen therapy (ltot) or home niv/cpap (even if only overnight) - neuromuscular disease - limitation of care based on patients' or physicians' decision