Inclusion Criteria:  Patients >18 years, Hospitalized in the Intensive Care Unit (ICU) with length of stay under 7 days Under positive pressure ventilation with no inspiratory effort, With hemodynamic instability (defined as abnormal peripheral perfusion or increased blood lactic or vasopressor infusion of norepinephrine >0.1 ug/kg/min to achieve adequate mean arterial pressure)  Exclusion Criteria:  Spontaneous ventilatory effort Lack of venous access Carrier of carbapenemase or clostridium difficile Lack of adequate superior vena cava (SVC) window (not allowing M-mode during both respiratory phases) Severe aortic regurgitation Impossibility to measure LVOT-VTI Extracorporeal membrane oxygenation.