Blood substitutes.

Substitutes for whole blood include blood fractions such as plasma, serum albumin and other fluids of various kinds which are not derived from blood but are used as plasma volume expanders; these, include the usual crystaloid intravenous solutions. Since in comparison to blood far more of these later solutions are given intravenously, a thorough knowledge of plasma volume expanders is essential. The first use of such expanders in human patients was by Hogan in 1915. He used colloidal gelatin and noted an improvement in blood pressure in shock. In 1945, Gronwall and Ingelman advocated the use of dextran in shock. The reguirements for an acceptable plasma substitute are: a satisfactory colloidal osmotic pressure, constand composition at reasonable cost, a viscosity suitable for intravenous administration, stability in prolonged storage at variable temperatures, and sterilization by autoclaving. Such substances must be either fully excreted or metabolized, and must cause no early or late tissue damage. They must be non-antigenic and pyrogen free. They must cause no change in the blood such as haemolysis, R.B.C. agglutination, increased sedimentation rate and no impairment of haemostasis. The presently available plasma expanders include blood derivatives (plasma, albumin), modified protein (gelatin, oxypolygelatin), polymerized carbohydrates (dextran) and plastics (polyvinyl pyrrolidone-PVP). All these substances expand plasma volume, decrease haematocrit and plasma proteins, increase sedimentation rate and blood pressure. Dextran, PVP and geletin do not alter hepatic function. Dextran and gelatin have no deleterious effects on renal function. Features of the clinically used plasma expanders are: 1. Fresh Frozen Plasma Fresh frozen plasma contains all clotting factors except platelets. The risk of the transmission of hepatitis is present as it is with whole blood. 2. Plasma Protein Fractions Plasma protein fractions are free of hepatitis virus, but may cause arteriolar dilatation and hypotension. 3. Serum Albumin Serum albumin is a concentrated blood protein fraction. It is salt poor, stable and does not transmit the virus of hepatitis. Since it has a high oncotic pressure it is necessary to give significant quantities of clear fluids with it. It is expensive, scarce, and dilutes the clotting factors. It is, however, a first choice for emergency treatment of shock; 4. Dextran The dextrans may be of medium or low molecular weight. They are inexpensive and readily available, and do not transmit the virus of hepatitis. In large amounts they cause a coagulation defect and may be antigenic. Continued.