Severe hypotension is a common life-threatening conditions in critically ill patients. Discriminating between the need for volume expansion or inotropic/vasoactive support is a main clinical goal. Pulse pressure variation are an accurate index of fluid responsiveness, but it needs controlled mechanical ventilation with a tidal volume of at least 8 ml/kg and absence of arrhythmias. This could limit its clinical applicability. Moreover pulse pressure variation accurately predicted cardiac output increment. However the cardiac output increase is not a clinically relevant target in absence of low cardiac output.