Preload dependence assessment is difficult during prone position, and to date, no hemodynamic parameters have been validated to rationalize fluid loading in that position. This study aims to validate several hemodynamic parameters, using continuous cardiac output by pulse contour analysis and transpulmonary thermodilution.

Inclusion Criteria:

• ARDS patient
• mechanically ventilated in prone position
• sedated and paralyzed
• with continuous cardiac output monitoring by transpulmonary thermodilution and pulse contour analysis
• fluid loading as indicated by attending physician

Exclusion Criteria:

• Age below 18
• no affiliation to social security
• Vena cava obstruction
• previous inclusion in protocol