Colloids

Regarding colloid preparations for intravenous infusion, which one of the following

statements is CORRECT?

a) Gelofusine® consists of urea-linked gelatin component molecules

b) Regarding pentastarches, the ‘pent’ refers to 50% esterification with succinyl groups

c) Dextran 70 and 110 interfere with platelet aggregation and have an anticoagulant

action, whereas Dextran 40 does not

d) Gelatin used for medical colloids is derived from exposing collagen from sheep

bones to a strong alkali then boiling water

e) Hetastarch contains molecules with mean molecular weight of 450 kDa

Answer: E

Explanation

A colloid is a suspension of molecules of a particular size in another continuous

medium. It is someway between a true suspension and a true solution because

although the added molecules are not dissolved in the carrier liquid, they will not

settle out of it under the action of gravity. The suspended particles will not traverse a

semi-permeable membrane, which is the rationale for their use as a plasma substitute

in hypovolaemia as the infused volume will remain in the intravascular compartment

(or at least it will not be distributed over larger fluid compartments as quickly as

crystalloid solutions). Aside from blood component therapy there are three main

categories of colloid solutions: gelatin preparations, hydroxyethyl starches and dextrans.

Gelatin is a collagen-like substance manufactured by boiling cattle bones (thermal

degradation) following alkali treatment (although it may be derived from boiling

up most animal connective tissues). The gelatin molecules are then urea-linked to form

the colloid particles in Haemaccel® or succinylated for use in Gelofusine®. They have

average molecular weights of 35 and 40 kDa respectively. Hydroxyethyl starches are

glucose backbones with hydroxyethyl esterification to different extents, which lends

them their name. Hetastarches have 70% substitution, hexastarches 60%, pentastarches

50% and tetrastarches 40% hydroxyethyl substitution. They have mean molecular

weights of 450, 250, 200 and 130 kDa respectively. Haes-steril® is a pentastarch while

Voluven® is a tetrastarch. Dextrans are polysaccharides derived from the action of the

bacterium Leuconostoc mesenteroides on sucrose. They are presented in preparations of

average molecular weights 40, 70 and 110 kDa, hence their names. They all interfere

with platelet aggregation and have at least the potential to interfere with blood crossmatching.

Each of the colloid preparations has different intravascular residence time,

metabolism/excretion rate and rate of immune-mediated adverse reactions, as well as

lists of other advantages and disadvantages.