Hypovolemia and acute circulatory failure affects more than 60% of patients hospitalized in intensive care or resuscitation. The volume expansion (VE) by fluid replacement therapy is the first treatment improve circulatory function. However, too much VE can be harmful. So, the use of dynamic predictive indicators of fluid responsiveness is recommended in patients with sepsis.In patients with spontaneous ventilation, few studies have evaluated these parameters. In mechanical ventilation, indices based on the respiratory variation of the diameters of vena cava have been studied and validated to predict the response to VE. However there is no similar study in spontaneously breathing patients without ventilatory support. The investigators hypothesize that the respiratory variations in the IVC diameters and femoral artery flow during standardized respiratory cycles are predictive factors of fluid responsiveness in spontaneously breathing patients with sepsis, acute circulatory failure, and regular cardiac rhythm.

Inclusion Criteria:

• Adult patients of the intensive care units of the Lille university-hospital and of the Valenciennes general hospital.

• Age greater than or equal to 18.

• Patient insured

• Spontaneous breathing without ventilatory support or intubation or tracheotomy.

• Regular cardiac rhythm

• Prescription by the physician in charge of the patients of a 500 mL volume expansion in less than 30 minutes.

• Patients with sepsis with at least one sign of acute circulatory failure:

  • Tachycardia with heart rate> 100/min
  • systolic blood pressure <90mmHg or a decrease >40mmHg in previously hypertense patient
  • Oliguria <0.5ml/kg/hour for at least one hour
  • skin mottling

Exclusion Criteria:

• high-grade aortic insufficiency
• transthoracic echogenicity unsuitable for measuring the stroke volume or inferior vena cava diameters
• clinical signs of active exhalation
• clinical or ultrasonographic evidence of pulmonary edema due to heart failure
• pregnancy
• abdominal compartment syndrome
• Irregular cardiac rhythm