Haemodynamic optimization is of paramount importance in septic shock, but is really consensual and standardized during the first 6 hours of treatment. Haemodynamic treatment including fluid loading management, vasoactive treatment and oxygen transport optimization is mainly based on expert recommendations or non-randomized trials. Recently, preload dependence indexes such as pulse pressure variation have been shown to be more accurate to predict fluid responsiveness than static indexes such as filling pressures. However, whether using preload dependence indexes changes septic shock prognostic remains to date unknown. The aim of this non-blinded randomized controlled trial is to assess whether haemodynamic optimization using preload dependence indexes and pulmonary thermodilution 1. reduces septic shock duration assessed by administration duration of vasoactive treatment (primary end point), 2. reduces regional hypoperfusion assessed by arterial lactate, 3. reduces lung hydrostatic oedema linked to excessive fluid loading (assessed by PaO2/FIO2 ratio and extravascular lung water). 4. reduces organ dysfunction (assessed by the SOFA score), ICU stay and 7 and 28 day mortality Control group is managed with an algorithm using filling pressures to drive haemodynamic treatment.