for the pneumonia arm of the study: inclusion criteria: * patients admitted to hospital with community acquired pneumonia. * acute respiratory failure spo2/fio2 \< 315 (spo2\<90% on room air or \<97% on 2l nc).

for the pneumonia arm of the study: inclusion criteria: * patients admitted to hospital with community acquired pneumonia. * acute respiratory failure spo2/fio2 \< 315 (spo2\<90% on room air or \<97% on 2l nc).

for the pneumonia arm of the study: inclusion criteria: - patients admitted to hospital with community acquired pneumonia. - acute respiratory failure spo2/fio2 < 315 (spo2<90% on room air or <97% on 2l nc).

for the pneumonia arm of the study: inclusion criteria: - patients admitted to hospital with community acquired pneumonia. - acute respiratory failure spo2/fio2 < 315 (spo2<90% on room air or <97% on 2l nc).

for the pneumonia arm of the study: inclusion criteria: - patients admitted to hospital with community acquired pneumonia. - acute respiratory failure (sao2/fio2 < 315 or pao2/fio2 < 300).

for the pneumonia arm of the study: inclusion criteria: - patients admitted to hospital with community acquired pneumonia. - acute respiratory failure (sao2/fio2 < 315 or pao2/fio2 < 300).