Study of End Tidal Carbon Dioxide (EtCO2) Variation After an End- Expiratory Occlusion Test as a Predictive Criteria of Fluid Responsiveness in Mechanically Ventilated Patients

Hypovolemia is one of major factor of haemodynamic instability. Fluid administration is not totally riskless. Indeed, it can create or inflate pulmonary oedema, alter gaz exchanges and increase post operative respiratory complications. Furthermore, fluid administration is not always followed by a cardiac output increase. Predicting preload responsiveness before administering fluid by reliable and reproductible methods is necessary in critically ill patients. Dynamic indicators are approved at the bedside such as passive raising leg test, pulse pressure variation, respiratory variation of the diameter of the superior vena cava. However, all these tests cannot be used for all patients. For example in the cases of spine or pelvis injury, or traumatic brain injury, patients with difficult condition for transthoracic echography. The investigators hypothesize that EtCO2 (end tidal carbon dioxide) variation after an 15 seconds end-expiratory occlusion test could predict fluid responsiveness in mechanically ventilated patients in the intensive care units. EtCO2 is a parameter which can be easy to collect, reproductible, and totally non invasive. This method could be especially appropriate for patients for whom the classical test of fluid responsiveness cannot be used