Outline the ideal properties of a colloid intravenous fluid. (25% marks) Compare and contrast Gelatins, Hydroxyethyl starch and 4 % Albumin solutions. (75% marks)
The ideal properties of a colloid include: stability at room temperature and long shelf life, lack of complications such as antiginicity, toxicity, pyrogenicity, disease transmission, or other adverse effects (eg coagulapathy) and plasma volume expansion lasting several hours. Candidates performed well in this section. Marks were equally divided between each colloid, and this part of the answer was well suited to table format. Candidates were expected to compare and contrast fluid source, infection and antigenic risk, cost and resource issues, packaging and ease of administration, duration of effect, tonicity, and properties which determine their side effect profile etc. Common errors were omission of adequate detail for each colloid and not being aware that Dextran is not a Hydroxyethyl starch.
Syllabus – E2a 2a
Reference: Foundations of Anaesthesia: Basic clinical Science, Hemmings and Hopkins, pg
This question very clearly references The Fluid Book by Kerry Brandis. Specifically, the linked page from his online fluid physiology textbook matches the wording of the examiner comments a little too precisely to be purely coincidental. Moreover, if one takes the time to track down this reference offered by the examiners, one will also note that it contains nothing whatsoever about "ideal" colloids.
And now, for the three colloids they asked about, and their properties:
|Gelatins||Hydroxyethyl starch||4% albumin|
|Fluid source||Succynylated bovine gelatin||Maize or corn||Human donated or apheresis blood|
|Carrier||0.9% NaCl||0.9% NaCl||0.9% NaCl|
|Bacterial infection risk||Minimal||Minimal||Minimal|
|Viral infection risk||Zero; but CJD not ruled out||Zero||
Virtually zero (but not zero); also CJD not ruled out
|Antigenic risk||Anaphylactogen||Anaphylactogen||Rarely, causes allergic reactions|
|Packaging||PVC flexible bags;
long shelf life (yrs)
PVC flexible bags;
long shelf life (yrs)
shorter shelf life (months)
Ease of administration
|No harder to administer than any other IV fluid||No harder to administer than any other IV fluid||In some health services, requires consent. Otherwise no harder to administer than any other IV fluid|
Duration of effect
|4-6 hrs||6 hrs (related to molecular weight)||6-12 hrs (variable; less in critically ill patients)|
Properties which determine the side effect profile
|Can decrease clot integrity by being incorporated into clots||Causes renal failure and pruritis||Appears to increase mortality in traumatic brain injury patients|
Ogemdi, Iwuozor Kingsley. "Properties and Uses of Colloids: A Review." Colloid and Surface Science 4.2 (2019): 24.
Roberts, Joan S., and Susan L. Bratton. "Colloid volume expanders." Drugs 55.5 (1998): 621-630.
Dasta, Joseph F., Adrienne D. Ross, and David M. Angaran. "Colloids vs. crystalloids—a continuing controversy." Drug intelligence & clinical pharmacy 18.3 (1984): 202-212.