Tryptophan, Serotonin and Kynurenine in Septic Shock

Inclusion Criteria: * Age above or equal to 18 years * Strong presumption clinical sepsis * Need for mechanical ventilation * Body temperature above 38°C or below 36°C * Heart rate above 90 bpm * Systolic blood pressure of \<90mm Hg despite adequate fluid replacement or a need for vasopressors less than 3 hours * Presence of at least one of the following criteria: * Ratio of arterial oxygen tension over inspired fraction of oxygen of less than 300 mm Hg * Urinary output below 0.5 mL per kg of bodyweight per h or below 30 mL/h (for at least 1 h) * Arterial lactate concentration above 2 mmol/L * Consent signed Exclusion Criteria: * Age below 18 years * Pregnancy * Underlying disease with a poor prognosis, a life expectancy of less than 24 hours * Depression or melancholy * Neuropsychiatric diseases: Seizure, manic psychosis, Migraine, or Drug addiction * Neuroendocrine tumors * Obstructive cardiomyopathy or acute myocardial ischaemia * Pulmonary embolism * Advanced stage cancer, malignant haemopathy, or AIDS with a decision to withhold or withdraw aggressive therapies * Inclusion in another clinical trial * Patient who receive before inclusion one of the following treatment known to modify serotonin level: almotriptan, amitriptyline, amoxapine, citalopram, clomipramine, clozapine, desipramine, dihydroergotamine, dolasetron, dosulepin, doxepin, eletriptan, ergotamine, flunarizine, fluoxetine, fluvoxamine, granisetron, imipramine, indoramin, interferon Alfa, interferon alfacon-1, interferon beta, iproniazid, maprotiline, methysergide, mianserin, Milnacipran, mirtazapine, moclobemide, naratriptan, olanzapine, ondansetron, oxetorone, paroxetine, pizotifen, risperidone, sertraline, sumatriptan, tianeptine, trimipramine, tropisetron, venlafaxine,viloxazine, zolmitriptan. * No consent