Colloid oncotic pressure (COP)

Colloid oncotic pressure (COP) is a physiological force exerted by plasma proteins, primarily albumin, that pulls water into the circulatory system from the interstitial space. It acts as the principal counter-force to capillary hydrostatic pressure, maintaining the balance of fluid exchange across the microvascular endothelium as described by the Starling equation [1]. When COP decreases, often due to hypoalbuminemia in conditions like liver cirrhosis or nephrotic syndrome, fluid leaks into tissues, resulting in edema or ascites [2]. While COP itself is a physical property rather than a single molecular receptor, it is therapeutically manipulated through the administration of colloid solutions, such as human albumin or synthetic starches [3]. These treatments aim to restore intravascular volume and improve hemodynamic stability by increasing the osmotic gradient within the blood vessels. Monitoring COP is critical in critical care settings to manage fluid resuscitation and prevent complications like pulmonary edema [1].

Other names

Oncotic pressureColloid osmotic pressurePlasma oncotic pressureProtein osmotic pressure

Colloid replacement therapies increase the concentration of large, non-diffusible proteins or polymers in the plasma, thereby raising the oncotic pressure to draw or retain fluid within the intravascular space and counteract hydrostatic pressure [1][3].