Purpose of review: The physiology of the venous part of the human circulation seems to be a forgotten component of the circulation in critical care medicine. One of the main reasons, probably, is that measures of right atrial pressure (Pra) do not seem to be directly linked to blood flow. This perception is primarily due to an inability to measure the pressure gradient for venous return. The upstream pressure for venous return is mean systemic filling pressure (Pmsf) and it does not lend itself easily to be measured. Recent clinical studies now demonstrate the basic principles underpinning the measure of Pmsf at the bedside.
Recent findings: Using routinely available minimally invasive monitoring of continuous cardiac output and Pra, one can accurately construct venous return curves by performing a series of end-inspiratory hold maneuvers, in ventilator-dependent patients. From these venous return curves, the clinician can now finally obtain at the bedside not only Pmsf but also the derived parameters: resistance to venous return, systemic compliance and stressed volume.
Summary: Measurement of Pmsf is essential to describe the control of vascular capacitance. It is the key to distinguish between passive and active mechanisms of blood volume redistribution and partitioning total blood volume in stressed and unstressed volume.