No approval from EC obtained. More details for study were required by EC.

The acute respiratory distress syndrome (ARDS) is common condition in critical ill patients affecting 7.2 people / 100,000 population / year and more than 7% of patients with invasive mechanical ventilation for more than 24 hours. ARDS carries a high hospital mortality of up to 48% and consumes large amounts of critical care resources. ARDS patients often present with severe hypoxemia that is refractory to conventional treatment and are thus evaluated for extracorporeal membrane oxygenation (ECMO). However, uncertainty regarding the appropriate indication for ECMO and clinical evidence for ECMO as a rescue treatment are still controversial. In 2012 Grasso and colleagues therefore presented a case series of influenza A (H1N1) ARDS patients describing the use of esophageal pressure measurements for individualized PEEP titration to achieve an end expiratory plateau pressure of the lung (PPLATL) of 25cm H2O. After performing the measurements in 14 patients, ventilator settings could be adjusted in half of these patients by increasing PEEP which resulted in an increase of oxygenation measures to an extend that criteria for extracorporeal support where no longer met and conventional treatment with invasive mechanical ventilation could be continued. However, uncertainty remains as to whether these results are generalizable to ARDS of any cause. In addition, increasing PEEP might impact on cardiac function and might therefore be associated with clinical important hemodynamic effects in these patients.

The investigators aim to evaluate hemodynamic changes in patients with severe ARDS in which an individualized PEEP treatment strategy can be employed. ARDS will be defined and stratified according to the Berlin ARDS definition. A naso-gastric probe capable of measuring esophageal pressure will be inserted directly after admission to the ICU as previously described. Invasive mechanical ventilation and oesophageal pressure measurements will be done using the GE Healthcare Carescape R860 ventilator. A pulmonary artery catheters (Edwards CCOcomb) will be inserted to evaluate the hemodynamic parameters of cardiac output, pulmonary artery pressures and left atrial pressures. Volumetric parameters will be measured using tanspulmonary thermodilution devices (Edwards EV1000). Cardiac function will be addressed in addition by the use of a predefined echocardiography protocol.

Inclusion Criteria:

1. Patients referred to our ICU for treatment of ARDS of any cause with a P/F ratio < 150 and indication for continued maximum critical care therapy
2. Male or female aged > 18 years
3. Written informed consent prior to study participation
4. The subject is willing and able to follow the procedures outlined in the protocol

Exclusion Criteria:

1. Patients admitted for primarily left ventricular or biventricular heart failure who are exclusively in need of cardiac and not pulmonary mechanical assist
2. Pregnant and lactating females
3. Patient has been committed to an institution by legal or regulatory order
4. Participation in a parallel interventional clinical trial
5. The subject received an investigational drug within 30 days prior to inclusion into this study

Adult patients referred to our ICU (Criitical Care Unit) for treatment of ARDS of any cause with a P/F ratio < 150 and indication for continued maximum critical care therapy. Patients of childbearing age with ARDS will be included.