Changes in Refractory Acute Respiratory Distress Syndrome (ARDS) Patients Under High Frequency Oscillation-ventilation

The study is intended to evaluate the hemodynamic and the indexed extrapulmonary lung water (ELWI) changes in patients treated by high frequency oscillation-ventilation (HFO-V) for refractory acute respiratory distress syndrome (ARDS). HFO-V may be used as rescue treatment in refractory ARDS but its hemodynamic impact is discussed. Moreover, as Extra Vascular Lung Water (a transpulmonary thermodilution parameter) was proven to be an independent mortality factor in ICU-patients, the investigators decided to monitor it in all ARDS patients who ended up needing HFO-V, from HFO-V plugging under 72 hours of this type of ventilation. All ARDS patients underwent high Positive End Expiratory Pressure (PEEP) with "protective ventilation" and those who remained below a PaO2/FiO2 ratio of 120 after 24h will be considered as "refractory ARDS patients" and, therefore eligible. They will be monitored by the transpulmonary thermodilution PiCCO technique (Pulsion Medical System. Munich, Germany) and placed under HFO-V. Both transpulmonary thermodilution measurements (ELWI , Cardiac Output, Global End-diastolic Volume) and standard transthoracic echocardiographic measurements (Ejection Fraction, End-diastolic Right and Left Ventricular Area, preload indexes) were be performed from HFO-V plugging to Day 3. The investigators suggest that ELWI will be correlated to HFO-V responsiveness and that cardiac output will not change at the HFO-V plugging, regardless of preload indexes variation. Inclusion will be proceeded over a 2 year period and, according to the population, the investigators expect about 50 eligible patients.