Time Course Evolution of Cardiac Output

The study will be conducted in four medico-surgical ICUs in France between April 2016 and April 2018. Since fluid challenge and invasive monitoring by thermodilution device is standard of care for septic shock management, the institutional review board waived patient consent. All patients and/or their next of kind will receive written information. Eligible patients will have to present an acute circulatory failure for whom the physician in charge will decide to start a fluid expansion. Hemodynamic variables will be obtained through transpulmonary thermodilution and pulse contour analysis (PICCO2 device, Pulsion Germany). Fluid expansion will consist in the infusion of 500 ml of saline through a central venous catheter in a standardized 10-minutes period. The duration of infusion will be controlled by an airbag pressurized at 300 mmHg. Fluid responsiveness will be defined by an increase in cardiac output over 15-per-cent from baseline (before fluid expansion). Study design: At time of decision to make the fluid expansion, a calibration of the PICCO2 device will be performed and a first set of hemodynamic measurements will be collected (cardiac output, cardiac function index, extravascular lung water, permeability vascular pulmonary index, global end diastolic volume, arterial pressure, heart rate). Then, fluid expansion will be administrated in less than 10 minutes. From the start of fluid expansion to the end of the two-hours period ot time, pulse contour cardiac output and arterial pressure will be continuously recorded. During the whole two hours period, no change in vasopressor dosage nor mechanical ventilation settings will be allowed. In case of hemodynamic instability, defined by a mean arterial pressure under 65mmHg, a new fluid expansion could be realized. In this last case, the protocol will start again from the beginning.