Résumé : This thesis highlights the early occurrence of microcirculatory perfusion and reactivity alterations and their association with subsequent organ failure during sepsis and with severity and prognosis in circulatory shock. It also shows the potential deleterious role of normobaric hyperoxia in the microcirculation perfusion. On the other hand, administration of nitrate and ischemic preconditioning make it possible to improve microcirculatory tolerance to hypoxic challenges and to sepsis, respectively. These therapies are promising lines of research that should be tested further.