Evaluation of the Effect of Dexmedetomidine on Phenylephrine Response During Refractory Septic Shock

Inclusion Criteria: * Age ≥ 18 years old * Septic shock, defined by the "Sepsis-3" criteria * proven or suspected infection, with modification of the SOFA score ≥ 2 points, * with persistent hypotension requiring vasopressors to maintain MAP ≥ 65 mmHg * and a serum lactate level \> 2 mmol/L despite adequate vascular filling * Adequate vascular filling: ≥ 30ml/kg, OR absence of preload-dependency criteria at time of assessment (respiratory variability of the inferior vena cava, passive leg lift, pulsed pressure variation) * Catecholamine resistance, defined by the need for a dose of norepinephrine ≥ 0,5 µg/kg/min for more than 2 consecutive hours within 24 hours of admission to intensive care unit * persistence of circulatory failure with at least one of the following criteria present in the 2 hours prior to randomisation: hyperlactatemia \> 2mmol/l, and/or mottling (≥ 1 score), and/or oliguria (diuresis \< 0,5 ml/kg/h over the last 2 hours) * Invasive Mechanical ventilation * Under sedation by midazolam or propofol * Informed consent obtained from a relative for patient included in an emergency * Patient affiliated to the national health insurance system Exclusion Criteria: * Cardiac arrest before inclusion and occurring before septic shock criteria are met * Cardiac index \< 2.2 l/min/m² after volume correction, or left ventricular ejection fraction \< 40% on echocardiography * Bradycardia \< 55 bpm (apart from treatment with β-blocker) or 2nd or 3rd degree BAV not equipped * Proven or suspected decompensation of coronary heart disease * Acute cerebrovascular condition within 2 weeks prior to inclusion * Severe hepatic insufficiency with TP and factor V \<50% in the absence of DIC (disseminated intravascular coagulation) * Patient on adrenaline or vasopressors at the time of inclusion (epinephrine or vasopressin stopped prior to inclusion is not a criterion for non-inclusion) * Patient on non-selective MAOI iproniazid within 15 days of inclusion * Patient for whom a decision has been made to limit the use of therapies * Hypersensitivity to dexmedetomidine or phenylephrine * Patient on dexmedetomidine before inclusion * Person subject to a legal protection measure (curatorship, guardianship) * Person subject to limited judicial protection * Pregnant, parturient or breastfeeding woman * Patient with suspected or confirmed mesenteric ischemia