the investigators will include 120 patients with a diagnosis of septic shock in accordance with the definition given by the 2001 expert consensus. Two groups of patients are likely to participate in this study: Patient hospitalized in intensive care for a septic shock = Primary patient + patient who develops, the waning of his hospitalization in intensive care for another reason, a septic shock = Secondary patient. Haemodynamic monitoring by transpulmonary thermodilution allow a patient's close monitoring during the initial phase supported. The clinical and biological data, demographic and the severity scores are collected for each patient during the first three days of stay. To predict the unfavorable evolution of the patients, a measure of the SOFA score at the input (J0) and third day (J2) is performed. the investigators analyzed mortality at day 28 in patients with increased P₍ᵥ-ₐ₎CO₂ and those with increasing of organ failure. This research will be conducted according to good clinical practice. An information will be distributed to patients.

Inclusion Criteria:

• Patient with a diagnosis of septic shock
• Initial lactate in patients should be≥ 2 mmol / L.
• The presence of circulatory insufficiency defined by a systolic blood pressure ≤ 90 mmHg (or a drop in blood pressure≥ 50 mmHg in hypertensive patients)
• One or more of the following: oliguria defined as diuresis≤ 0,5 mL/ kg / h for at least two hours; the presence of signs of cerebral hypoperfusion; the highlighting of mottling
• The presence of a femoral arterial catheter and a central venous line in the superior vena cava position
• Hemodynamic monitoring with semi-invasive monitoring of cardiac output with thermodilution

Exclusion Criteria:

• Patient no longer in the initial phase of septic shock
• Absence of semi-invasive cardiac monitoring with thermodilution
• Vulnerable people
• Absence of informed consent