Classify colloid intravenous fluids and outline the pharmacology of the hydroxyethyl starches.
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
Classification of colloids:
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 |