 Septic shock is a frequent syndrome with a 45 mortality rate despite intensive care unit ICU care, where free radicals may play a key role, and a 40 decrease in plasma selenium concentration is observed. Selenium is a trace element with both indirect enzymatic anti-oxidant, and direct oxidant properties. High dose of sodium selenite administration could increase antioxidant cells capacities, and reduce inflammation by a direct paradoxical pro-oxidative effect. We conduct a study to evaluate the effects of selenium treatment in comparison to placebo, in septic shock patients. Efficacy will be evaluated by the weaning time of catecholamines. 