Shock related to acute vasodilation is called 'distributive shock'. When pathologic dilation of peripheral vascular beds occurs, blood pools in the periphery and does not return to the central system (i.e right heart). This loss of preload can spiral a patient into cardiovascular collapse if not rapidly treated. Vasopressors are the tools we use to combat distributive shock. They act on vascular smooth muscle receptors to constrict the vascular beds. Most of the pressor agents we use in the ICU are synthetic analogs of endogenous catecholamines.(e.g. norepinephrine, epinephrine). Most of these agents work via adrenergic receptors on the vascular smooth muscle cells. Vasopression acts via a separate set of vascular smooth muscle receptors called 'V' receptors.