What is the main source of plasma colloid osmotic pressure

The plasma colloid osmotic pressure is mainly maintained by plasma proteins, among which albumin contributes the most, accounting for about 75% -80%. The influencing factors include albumin concentration, globulin level, fibrinogen content, blood dilution status, and capillary permeability.

1. Albumin function:

Albumin is the core substance that maintains plasma colloid osmotic pressure, with a small molecular weight and negative charge, and can effectively retain water in blood vessels. The normal adult plasma albumin concentration is about 35-50g/L, and each 1g of albumin can produce an osmotic pressure of about 5.54mmHg. Hypoproteinemic edema occurs when synthesis is reduced due to liver disease or malnutrition.

2. Effect of Globulin:

Globulin accounts for 35% -40% of the total plasma protein, including three types: alpha, beta, and gamma. Although the molecular weight is large and the osmotic effect is weak, when the globulin is abnormally increased in patients with chronic inflammation or myeloma, it indirectly increases the colloid osmotic pressure by increasing the plasma total protein concentration. Immunoglobulin IgG produces only about 1.4mmHg osmotic pressure per 1g.

3. Participation of fibrinogen:

Fibrinogen, as a coagulation factor, accounts for 4% -6% of plasma protein and has a molecular weight of up to 340000 daltons. During acute phase reactions or trauma, the concentration increases. Although the osmotic activity is low, it can indirectly regulate interstitial fluid reflux by increasing plasma viscosity and affecting microcirculation dynamics.

4. Blood dilution effect:

When a large amount of infusion or water poisoning leads to blood dilution, the decrease in plasma protein concentration will cause a decrease in colloid osmotic pressure. For every 10% dilution of blood volume, the colloid osmotic pressure decreases by approximately 1.5-2mm Hg. This situation is common in patients with excessive fluid replacement or renal dysfunction after surgery.

5. Vascular permeability: In pathological conditions such as burns and sepsis, the enlargement of the capillary endothelial gap leads to albumin leakage. Although the total amount of plasma protein remains unchanged, the effective colloid osmotic pressure inside the blood vessels decreases, while the interstitial fluid colloid osmotic pressure increases, forming a dual osmotic pressure gradient imbalance.

To maintain stable plasma colloid osmotic pressure, attention should be paid to protein metabolism balance. Daily intake of 1.2-1.5g/kg of high-quality protein is recommended, and high-value foods such as fish, egg whites, and whey protein should be prioritized. Cirrhotic patients can supplement branched chain amino acids to avoid blood dilution caused by excessive drinking after vigorous exercise. Regular testing of serum prealbumin can more sensitively reflect nutritional status. When sunken edema or eyelid edema occurs in both lower limbs, it is recommended to promptly check liver function and urinary protein indicators.