<qa>  What is the most common cause of Septic shock?Septic shock - an uncontrolled systemic host response to invasive infection -, leading to multiple organ failure, is a public health issue because of its frequency 11000 inhabitants per year, its cost and its 45 mortality rate, remaining high despite all the improvements made in ICU for the past 20 years. His physiopathology is better understood with increasing data supporting the key role of free radicals, and a more than 40 plasma selenium concentration decrease that maybe associated with increased morbidity and mortality. Meanwhile, for the past 30 years, researches have been conducted on the essential trace element selenium for its requirement for key antioxidant enzymes, through the 21st aa selenocystein, and also for its potentially toxic, pro-oxidant properties. In septic shock, both properties may be useful, antioxidant enzymatic to increase cell defense especially endothelial cells, and direct pro-oxidant action to decrease the genomic response, especially on phagocytic cells. 