Pharmacology: Albumin is a highly soluble, globular protein (MW 66, 500), accounting for 70-80% of colloid osmotic pressure of plasma. Therefore, it is important in regulating the osmotic pressure of plasma. Human Albumin 20% supplies the oncotic equivalent of approximately 5 times its volume of human plasma. It will increase the circulating plasma volume by an amount approximately 3.5 times the volume infused within 15 minutes, if the recipient is adequately hydrated. This extra fluid reduces hemoconcentration and decreases blood viscosity. The degree and duration of volume expansion depend upon initial blood volume. When treating patients with diminished blood volume, the effect of infusion albumin is administered to individuals with normal blood volume. Albumin is also a transport protein and binds naturally occurring, therapeutic, and toxic materials in the circulation. Albumin is distributed throughout the extracellular water and more than 60% of the body albumin pool is located in the extravascular fluid compartment. The total body albumin in a 70 kg man is approximately 320 g; it has circulating life span of 15-20 days, with a turnover of approximately 15 g per day.
Pharmacokinetics: Under normal conditions, the total exchangeable albumin pool is 4-5 g/kg body weight of which 40-45% is present intravascularly and 55-60% in the extravascular space. Abnormal distribution may occur in conditions such as severe burns or septic shock, where capillary function is impaired. Increased capillary permeability will alter albumin kinetics. Under normal conditions, the average half-life of albumin is about 19 days. The balance between synthesis and breakdown is normally achieved by feed-back regulation. Elimination is predominantly intracellular and due to lysosome proteases. In healthy people, less than 105 infused albumin leaves the intravascular compartment during the first 2 hour following infusion. As a result, the circulation volume will increase from 1 to 3 hours administration. There is considerable individual variation in its effect of plasma volume. In some patients the plasma volume can remain increased for some hours. However, in ill patients, albumin can leak out of the vascular space in substantial amounts at an unpredictable rate.