Plasma substitutes expanders

Oligemic shock may be managed by rapid infusion of blood plasma or plasma substitutes/expanders and simultaneously the source of blood / fluid loss in identified and corrected. 

Plasma substitutes/expanders are high molecular weight substances when infused intravenously into blood stream retain fluid in the vascular compartment and exert oncotic pressure. But before infusing into the blood stream, the following requirement may be present. 

Dextrans are produced commercially for use as plasma substitutes (plasma expanders) which can be administered by intravenous injection to maintain or restore the blood volume. They can be used in applications to ulcers or bum wounds where they form a hydrophilic layer which absorbs fluid exudates. 

To eliminate the threat of shock, replenishment of the circulation is essential. With moderate loss of blood, administration of a plasma volume expander may be sufficient Blood plasma consists basically of water, electrolytes, and plasma proteins. However, a plasma substitute need not contain plasma proteins. These can be suitably replaced with macromolecules ( colloids ) that like plasma proteins, (1) do not readily leave the circulation and are poorly filtrable in the renal glomerulus and (2) bind water along with its solutes due to their colloid osmotic properties. In this manner, they will maintain circulatory filling pressure for many hours. On the other hand, volume substitution is only transiently needed and therefore complete elimination of these colloids from the body is clearly desirable. 

In addition to murein, bacterial polysaccharides include dextrans—glucose polymers that are mostly al 6-linked and al 3-branched. In water, dextrans form viscous slimes or gels that are used for chromatographic separation of macromolecules after chemical treatment (see p.78). Dextrans are also used as components of blood plasma substitutes (plasma expanders) and foodstuffs. 

Plasma volume expanders and artificial blood substitutes... 

Dextran (O Scheme 5) solutions have been used as a plasma volume expander since 1947 owing to their non-immunogenic and well-tolerated nature as plasma substitutes [10]. Furthermore, since dextran suppresses erythrocyte aggregation and reduces blood viscosity, it has... 

Certain fractions of partially hydrolysed dextran are used as plasma substitutes or expanders. Certain strains of Leuconostoc meserentoides are cultivated to synthesise dextran (XIII), which is a polymer of anhydroglucose, linked through a-1,6 glucosidic linkages. The chains are branched on the average, one branch occurs for every 10-12 glucose residues. The intrinsic viscosity [ij is related to Mby the relationship... 

Use Blood plasma substitute or expander, confections, lacquers, oil-well drilling muds, filtration gel, food additive. 

Hetastarch is a plasma expander that produces expansion of plasma volume. It does not have oxygen-carrying capacity or contain plasma protein, so it is not a blood or plasma substitute. It is indicated as an adjunct therapy for plasma volume expansion in shock caused by hemorrhage, bums, surgery, sepsis, or other trauma and as an adjunct in leukapheresis to improve harvesting and increase yield of granulocytes. 

The plasma volume expanders are the substances that are transfused to maintain fluid volume of the blood in event of great necessity, supplemental to the use of whole blood and plasma. Some starch derivatives like hydroxyethyl starch and acetyl starch, which are a group of coUoids, are used to provide sustained intravascular volume expansion. Hydroxyethyl starches are high-polymeric compounds obtained via hydrolysis and subsequent hydroxyl ethylation of glucose units substituted at carbon number 2, 3, and 6 of starch. Recently some waxy starches were also evaluated for plasma volume expander, but more research is needed to establish them as a good substitute for the synthetic polymers. 

Hydroxyethylstarch (HES) is prepared from the amylopectin of waxy maize starch by hydrolysis and subsequent treatment with ethylene oxide. Amylopectin is a branched polyglucose composed of chains of a 1-4 linked glucose residues, to which a number of branches are attached by a 1-6 linkages (Aspinall 1970). When soluble amylopectin is intravenously injected into animals, it is rapidly degraded by a-amylase and is therefore unsuitable as a plasma substitute. For this reason Wiedersheim (1957) suggested substitution of amylopectin with hydroxyethyl groups to slow down the action of amylase and so extend its persistence in the circulation. He showed that such HES preparations had useful properties as plasma expanders and were relatively nontoxic. These results were subsequently confirmed and extended (Thompson et al. 1962, 1964, 1970). 

Thompson WL (1960) Plasma substitutes. A review. J SC Med Assoc 56 456-472 Thompson WL (1978) Hydroxyethyl starch. In Blood substitutes and plasma expanders. Liss, New York, pp 283-292... 

Hydroxyethyl starch has been widely used as plasma volume expander in bleeding patients. Each product is characterized by its molecular weight, concentration, molar substitution, origin, and solvent [44. Adverse reactions include excessive intravascular volume expansion, metabolic acidosis, anaphylaxis, renal dysfunction, hepatic dysfunction, and coagulopathy [45 ]. It has been suggested that adapting the formulation to the... 

Albumin. Investigation iato the safety of bovine plasma for clinical use was undertaken ia the eady 1940s ia anticipation of wartime need (26). Using modem proteia chemistry methods, including electrophoresis and ultracentrifugation, it was shown that most of the human adverse reactions to blood substitutes were caused by the globulin fraction and that albumin was safe for parenteral use. Human albumin is now used extensively as a plasma expander ia many clinical settings. 

The IV solutions of plasma expanders include hetastarch (Hespan), low-molecular-weight dextran (Dextran 40), and high-molecular-weight dextran (Dextran 70, Dextran 75). Plasma expanders are used to expand plasma volume when shock is caused by bums, hemorrhage surgery, and otiier trauma and for prophylaxis of venous thrombosis and diromboembolism. When used in die treatment of shock, plasma expanders are not a substitute for whole blood or plasma, but tiiey are of value as emergency measures until die latter substances can be used. 

The majority of blood substitutes currently in use function only as plasma expanders. These maintain blood pressure by providing vascular fluid volume after haemorrhage, burns, sepsis or shock. While standard electrolyte solutions, such as physiological saline, may be administered, their elfect is transitory as they subsequently dilfuse back out of the vascular system. 

Alternatively, colloidal plasma expanders (Table 9.3) are used. When administered at appropriate concentrations, they exert an osmotic pressure similar to that of plasma protein, hence vascular volume and blood pressure are maintained. The major disadvantages of colloidal therapy include its relatively high cost, and the risk of prompting a hypersensitivity reaction. Determined elforts to develop blood substitutes were initiated in 1985 by the US military, concerned about the issue of blood supply to future battlefields. 

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