Albumin, hetastarch, and pentastarch

Published on 07/02/2015 by admin

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Albumin, hetastarch, and pentastarch

Edwin H. Rho, MD

The colloid controversy

For decades, medical debate has continued over the value of colloid infusion in the perioperative setting. It is important to note, however, that in patients who are bleeding and who require intravascular volume expansion—especially patients with trauma—first-line therapy is the use of blood products. Early colloid advocates argued that it was important to maintain normal colloid osmotic pressure to keep intravascular fluid from passing into the tissues and thereby contributing to pulmonary, cerebral, subcutaneous edema or ascites. Albumin was the most widely used colloid until hydroxyethyl starch, and pentastarch were developed, and it still is commonly used.

Albumin

Albumin is available in 5% and 25% concentrations, the latter being most useful in patients who are unable to tolerate large volumes of fluid. Albumin is a heat-stable tightly wound protein molecule derived from human whole blood. It is heated to 60°C for 10 h to eradicate infectious organisms (both bacterial and viral). Transmission of Creutzfeldt-Jakob disease has not been reported with the use of albumin.

Hetastarch and pentastarch

Both hetastarch and pentastarch are composed of chains of glucose molecules to which hydroxyethyl ether groups have been added to retard degradation. The glucose chains are highly branched, being derived from the starch amylopectin. One in twenty glucose monomers branches. Starch chains of various lengths are present in hetastarch, giving it an average molecular weight of 450 kD. Its number-average molecular weight is 69 kD; this term describes a simple average of the individual molecular weights and is more closely related to oncotic pressure. About 80% of hetastarch polymers have molecular weights in the range of 30 to 2400 kD. Hetastarch is available as a 6% solution in 0.9% sodium chloride or a lactated electrolyte solution. The chemical and pharmacokinetic properties of hetastarch and pentastarch are listed in Table 100-1.

Table 100-1

Chemical and Pharmacokinetic Properties of Hetastarch * and Pentastarch

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Property	6% Hetastarch	10% Pentastarch
pH	5.5	5.0
MW_W (kDa)	450 (range, 10-1000)	264 (range, 150-350)
MW_N (kDa)	69	63
Calculated osmolar concentration (mosmol/L)	310	326
Molar substitution ratio	0.7	0.45
Intravascular half-life (h)	25.5	2.5
Renal elimination	Molecules smaller than 50 kDa are rapidly excreted; <10% detected intravascularly at 2 weeks	Molecules smaller than 50 kDa are rapidly excreted; undetectable intravascularly at 1 week

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