Inclusion criteria  1) Acute circulatory failure defined as:  SAP ≤ 90 mmHg (or a decrease > 50 mm Hg in hypertensive patients) or a mean arterial pressure (MAP) ≤ 70 mmHg or the use of vasopressors to maintain SAP >90 mmHg, associated with skin mottling; tachycardia ≥100 beats/min; urinary flow ≤0.5 mL/kg for at least 2 hours; blood lactate level ≥4 mmol/L.  Exclusion criteria:  known severe myocardial or valvular dysfunction cardiac arrhythmias severe acute respiratory distress syndrome on-going haemodialysis or continuous hemofiltration moribund patients persistent low quality of the arterial signal affecting hemodynamic monitoring measurements poor echographic windows.