Pathophysiology of systemic venous return during the acute circulatory failure

The systemic venous return is the flow of blood that is conducted from the peripheral systemic venous system toward the right heart. At equilibrium, the systemic venous return equals the cardiac output, as the venous and arterial systems operate in series. However, unlike the arterial system, the venous system is a capacitive system with a high compliance. It includes an unstressed volume, which is a reservoir of blood that can be recruited via a sympathetic stimulation, endogenous or exogenous (administration of vasoconstrictive agents). The model of Guyton enables to describe the three determinants of venous return: the mean systemic pressure, the right atrial pressure and the resistance to venous return. Recently, new methods have been developed to explore at the bedside of critically ill patients the systemic venous return and its determinants. In such a way, a pathophysiological approach of circulatory failure states through the study of systemic venous return allows a complete description of the underlying mechanisms and the analysis of the effects of the main treatments that are used in this context.