Thousands of patients in intensive care units (ICUs) throughout the world are treated with fluid therapy to restore effective blood volume and ensure optimal organ perfusion.
1,2 Fluid therapy includes a broad variety of products that are typically categorized as crystalloids and colloids. Although the goal is to use intravenous fluids to expand the intravascular space, fluid also moves into the extravascular space. Crystalloids are thought to counteract that movement via the osmotic pressure exerted by their solutes, whereas colloids are designed to exploit oncotic pressure gradients for the same effect.
2 Thus, theoretically, expansion of blood volume may be proportional to solute tonicity or oncotic power.