Hypovolaemia

Abstract

Fluid therapy has, traditionally, been guided by static markers of cardiac preload such as central venous pressure and pulmonary artery wedge pressure. Fluid responsiveness, or an increase in stroke volume in response to fluid, is poorly predicted by these variables. This has led to increased interest in variables such as the fluctuation in blood pressure and stroke volume in response to mechanical ventilation. These changes are caused by the reduction in venous return associated with positive-pressure ventilation, which, in turn, leads to a reduction in left ventricular stroke volume and arterial pressure. These cyclical changes, termed systolic pressure variation, pulse pressure variation and stroke volume variation, predict fluid responsiveness more accurately than static markers in positive-pressure ventilated patients with a stable cardiac rhythm. For patients with spontaneous respiratory efforts or an irregular cardiac rhythm, the response in stroke volume to a passive leg raise seems to show promise in its ability to predict fluid responsiveness.