In the investigators opinion, the ECOM system seems able to provide a monitoring tool which responds to all the expectations of a modern hemodynamic monitoring device. It uses a well known technique, the bioimpedance. The investigators suppose this device should be more efficient than the one that has been used before. Indeed, as the system is build on the endotracheal tube, it comes closer to the aorta, where all the measures are made, and the recorded signal should be less affected by the passage through the surrounding tissues.