Exclusion’s criteria
Patients were excluded from the study if they met one or more of the following criteria: not diagnosed with ARDS; not diagnosed with influenza A (H1N1); age younger than 18 years; evidence of acute myocardial infarction; cardiac arrhythmias (supraventricular tachycardia > 140 beats/min or complex ventricular ectopy) and heart failure. Patients with other causes of ARDS were excluded from the study since we wanted to investigate Influenza A (H1N1)-ARDS patients due to the lack of data within this specific group.