Plasma oncotic pressure (COP) (COP)

Plasma oncotic pressure, also referred to as colloid osmotic pressure (COP), is the osmotic pressure exerted by proteins—most notably albumin—within the blood vessels [1]. This pressure is a fundamental component of the Starling forces that regulate the exchange of fluid across the semipermeable capillary endothelium [2]. While hydrostatic pressure pushes fluid out of the vasculature, oncotic pressure acts as an inward-pulling force that keeps water within the circulatory system [3]. In conditions such as liver cirrhosis, malnutrition, or nephrotic syndrome, a decrease in plasma protein levels lowers this pressure, resulting in fluid leakage and systemic edema [3][4]. Therapeutic strategies involve the administration of colloid solutions, including human albumin and synthetic starches, to restore the oncotic gradient and expand intravascular volume [5]. Consequently, managing this pressure is vital in treating hypovolemia and maintaining tissue perfusion in critically ill patients. It is important to note that this is a physiological parameter reflecting a physical force rather than a discrete molecular receptor or enzyme.

Other names

Colloid osmotic pressureOncotic pressureCapillary colloid osmotic pressureCapillary oncotic pressure

Colloid replacement therapy involves the administration of large molecular weight substances that cannot easily cross the capillary endothelium, thereby increasing the intravascular osmotic gradient to pull fluid from the interstitial space back into the blood vessels [1][2].