Plasmavolume

Plasmavolume, commonly written as plasma volume, refers to the liquid component of blood that remains after the cellular elements are removed. It is a dynamic extracellular fluid compartment that constitutes roughly 50 to 60 percent of total blood volume. In an average adult, plasma volume is about 2.5 to 3 liters, though this varies with body size, hydration, and health status.

Plasma itself consists mainly of water and dissolved substances, including plasma proteins such as albumin, globulins, and fibrinogen, as well as electrolytes, nutrients, hormones, and waste products. The volume of plasma is a key determinant of circulatory volume and oncotic pressure, influencing fluid distribution between the intravascular space and the interstitial space.

Regulation of plasma volume involves fluid intake and losses, renal function, and hormonal controls. Antidiuretic hormone (vasopressin) promotes water reabsorption in the kidneys; the renin-angiotensin-aldosterone system enhances sodium and water retention; natriuretic peptides help to reduce volume. Changes in plasma volume occur with dehydration, illness, trauma, burns, and during transfusion or fluid therapy.

Clinical relevance includes its role in guiding fluid management in surgery, critical care, and emergency medicine. Hypovolemia is a reduced plasma volume that can compromise tissue perfusion, while hypervolemia refers to excess plasma volume that may cause edema and cardiac stress. Plasma volume can be estimated using dye- or tracer-dilution techniques, such as labeled albumin or Evans blue, and is sometimes assessed indirectly through hemodynamic or imaging methods.

Note: In plasma physics, the term plasma volume may describe the size of a plasma region within a device; in biomedical contexts, plasmavolume mainly denotes blood plasma volume.