Plasma expanders – Shock is a state of acute circulatory failure. It is mainly due to reduced blood volume (hypovolemia). It is, therefore, essential to restore the intravascular blood volume as quickly as possible by intravenous fluid therapy. The various types of fluids used for replacement are:
1. Whole blood and plasma
2. Plasma substitutes or plasma expanders:
a. Colloidal such as dextran, hydroxyethyl starches, polyvinyl pyrrolidone, oxypolygelatin.
b. Crystalline, e.g. normal sodium chloride and dextrose solution.
Plasma expanders are substances of relatively high molecular weight. On infusion, plasma expanders remain long enough to augment the volume of circulating fluid by increasing the osmotic pressure.
1. Dextran: It is originally isolated from beet sugar. In therapeutics, dextran having different molecular weight is used.
Dextran 40 (MW 40 million): 10% in dextrose or in sodium chloride intravenous infusion.
Dose of plasma expanders : Initial dose 500—1000 ml; the first 500 ml may be given in 30 minutes which may be followed by 100 ml by continuous infusion for 2—3 days. Be careful in patients with renal impairment, congestive heart failure or polycythaemia.
Dextran 70 (MW 70, 000) and dextran 110 (MW 110,000): 6% in dextrose or in sodium chloride intravenous infusion. They are used for the management of hypovolemic or haemorrhagic shock as plasma expanders.
Dextrans are probably almost ideal plasma expanders because they can be easily sterilized and can be stored for long time. However, rarely allergic reactions to these preparations may occur.
2. Polyvinylpyrrolidone: It is a synthetic water soluble preparation and important among plasma expanders. It has average molecular weight of 35,000—40,000. It is sterile 40% solution in buffered physiological saline. It has a tendency to bind with insulin and penicillin.
3. Gelatin: Commercially available gelatin has molecular weight of 30,000. It is among the commonly used plasma expanders and is given intravenously, 500—1000 ml of 3.5—4% solution, in low blood volume.
4. Electrolyte and water replacement: To meet normal fluid and electrolyte requirement, normal saline (sodium chloride, 0.9% w/v) is the most widely used intravenous preparation. It is indicated in fluid losses which are accompanied by sodium depletion as in severe diarrhoea, diabetic ketosis, in order to provide water and sodium ions in physiologically comparable amounts.
To replenish major fluid losses or to meet the daily water requirements dextrose intravenous infusion (5% w/v) is used. Its energy content is low. So it makes only a minimal contribution to the body’s requirement.