In patients presenting with the acute respiratory distress syndrome (ARDS), mechanical ventilation with low tidal volume (6 ml/kg predicted body weight) is the current gold standard for supportive care. However, despite a relative low tidal volume, approximatively one third of patients will experienced tidal hyperinflation, a phenomenon known to induce pulmonary and systemic inflammatory response. A further reduction of the tidal volume to 4 ml/kg (PBW) will prevent pulmonary area from tidal hyperinflation. As a result, hypercarbia and respiratory acidosis are commonly observed with such very low tidal ventilation. Extra corporeal CO2 removal is one of a mean to normalize arterial CO2 tension.

Patients with ARDS also frequently develop acute renal failure which may required Renal Replacement Therapy. Some data suggests that starting early the RRT may favor outcome.

The investigators hypothesized that a strategy combining ECCOR and RRT early in the course of patients presenting ARDS and acute renal failure will allow the tidal volume to be further reduced, providing lung protection, while avoiding the arterial CO2 tension to be increased.

For this purpose, the investigators sought to evaluate the safety and efficacy of adding a membranel oxygenator within an hemofiltration circuit, either upstream or downstream of the hemofilter.

Inclusion Criteria:

• Acute Respiratory Distress Syndrome according to the AECC definition
• Acute Renal Failure according to the RIFLE definition

Exclusion Criteria:

• Age < 18 years
• PaO2/FiO2 < 100 with FIO2 = 1 and PEEP > 18 cmH2O
• DNR order or death expected within the next 3 days
• Intracranial haemorrhage or hypertension
• Heparin allergy