Question 10

Classify colloid intravenous fluids and outline the pharmacology of the hydroxyethyl starches.

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College Answer

This question, of high and common clinical relevance, was poorly answered. Candidates were expected to mention colloid intravenous fluid were either semi-synthetic or plasma derivatives. A clear outline of the pharmacology, that is formulation (eg molecular weight, amylopectin/glucose polymer), pharmacokinetics and adverse effects, etc was expected of a good answer.

Syllabus: E2a
References: Hemmings, Foundation of Anaesthesia: Basic and Clinical Science pg 719, OH,
Intensive Care Medicine 5th Edition pg 927-929

Discussion

Classification of colloids:

  • Synthetic colloids
    • Polyvinylpyrrolidone
  • Semi-synthetic colloids
    • Gelatins (eg. gelofusine, polygeline, )
    • Dextrans (they are all called "dextran X", where X is the molecular mass in kDa)
    • Starches (eg. hydroxyethyl starch)
  • Plasma derivatives
    • Purified plasma proteins (eg. albumin, immunoglobulin)
    • Whole plasma products (eg. fresh frozen plasma)

Pharmacology of starches:

  Hydroxyethyl starch
Chemistry amylopectin/glucose polymer
Fluid source Maize or corn
Carrier 0.9% NaCl
Bacterial infection risk Minimal
Viral infection risk Zero
Antigenic risk Anaphylactogen
Cost Cheapest among colloids
Packaging

PVC flexible bags;

long shelf life (yrs)

Ease of administration

No harder to administer than any other IV fluid

Duration of effect

6 hrs (related to molecular weight)
Tonicity Isotonic
Clearance 40% renally cleared; 60% metabolised in the liver
Desirable effects

Increases the oncotic pressure of the circulating blood volume, thereby increasing the distribution of resuscitation fluid to this volume.

Adverse effects

Causes renal failure

Decreases clot integrity

Pruritis is a common side effect

May cause circulatory overload and APO