It is a prospective observational study, in two 15-bed intensive care units, including adult patients with septic shock who have a mean arterial pressure (MAP) < 65 mmHg within the first three hours after the start of resuscitation. For every patient, the physician taking care of the patient should have already decided to initiate NE or to increase its dose in order to achieve a MAP value of at least 65mmHg without any other change of the associated therapy (fluid administration, ventilator settings, other drugs). The study was approved by the institutional review board of our institution (Comité de Protection des Personnes, Paris-Ile-de-France VII). Informed patient (or next-of-kin) consent was obtained from all patients.