The water present in the body is compartmentalised – intra-cellular (present inside cells, about 2/3rd) and extra-cellular (outside cells, about 1/3rd). The extra-cellular fluid is present as plasma inside blood vessels (intra-vascular) or as fluid surrounding cells that does not circulate (interstitial). There is also some amount of trans-cellular fluid, which comprises tears, saliva, and gastric juice, CSF etc.
Albumin is the main plasma protein, which is responsible for 70-80% of the osmotic pressure of normal plasma (i.e. prevents blood from leaking out of the blood vessels). It is therefore required to regulate the volume of circulating blood. It also binds to substances present in the blood and thus acts as a transport protein. The amount of albumin present in the body is about 350 gm and this is distributed throughout the extra-cellular compartments. Its half-life is around 15 to 20 days and about 15 gm per day is synthesised by the liver. The minimum amount of albumin required to be present in the blood to prevent oedema is not precisely known but levels of 2.5 gm/dl prevent it.
Indications for its possible use are very limited and often there are alternatives that are cheaper and equally suitable. Some of the indications include a) hypovolemia i.e. reduction in the volume of blood that results in shock; b) hypoalbuminaemia due to inadequate synthesis (burns, malnutrition, etc.), increased utilisation & increased loss from the body (kidney disease) or redistribution in the body and c) Cardio-pulmonary bypass surgery. It is also used in haemolytic disease of the newborn to bind bilirubin.
The amount of albumin infused is patient-specific and dependent upon many factors including heart rate, blood pressure, presence and degree of shock, oncotic pressure, haemoglobin, haematocrit and venous and pulmonary congestion. Combating hypoalbuminaemia as such is not useful in seriously ill patients; it is the underlying disease that should be treated.