A vasodilatory shock is essentially characterized by the failure of the peripheral vascular smooth muscle cells to constrict, which results in altered tissue perfusion and organ dysfunction. Severe inflammation is the most prominent factor that triggers a vasodilatory shock, however, other non-related mechanisms could also be designated that lead to the same outcome. Arterial hypotension indicates one of the major signs of a vasodilatory shock and a progressively undermined response by the vascular smooth muscle to exogenous vasoconstrictors and endogenous circulating.

In normal conditions, the resistance arteries and arterioles’ vascular tone determines peripheral vascular resistance, contributing to blood flow and blood pressure regulation to and within the tissues.In general, an index is the ratio of one dimension of a thing to another dimension. DSI is based on three simple sequential thoughts: Under isovolemic conditions and continuous arterial compliance, shorter diastolic time is associated with higher DAP, while prolonged diastole leads to the opposite effect.

Indeed, classical observations demonstrated that pulse pressure variations are more significant when compliance changes at constant resistance than when resistance changes at constant compliance. One could interpret it as representing the arterial tone, while other parameters more directly confound the dependence of systolic arterial pressure on the arterial RC. Nevertheless, no clear signals are indicating when vasopressor support should be started. In this way, very early signals of severe vasodilation should alert on its possible immediate requirement, and as such, DSI could be an immensely useful tool for this purpose.

Ref: https://annalsofintensivecare.springeropen.com/articles/10.1186/s13613-020-00728-x