Question 1(p.2)

Outline the ideal properties of a colloid intravenous fluid. (25% marks) Compare and contrast Gelatins, Hydroxyethyl starch and 4 % Albumin solutions. (75% marks)

[Click here to toggle visibility of the answers]

College Answer

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
719

Discussion

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.

Properties of an ideal colloid
- Pharmaceutical properties:
  - No special storage requirements
  - No need for crossmatching, or interference with crossmatching
  - Long shelf life
  - Not susceptible to biological contamination (eg. by acting as a substrate for microbial growth, or by allowing donor-recipient viral transmission)
  - Cheap and readily available
  - Acceptable to all patients (i.e. no cultural objections)
- Pharmacokinetic properties:
  - No special limitations on volume that can be infused
  - Low viscosity
  - Distributed to intravascular compartment only
  - Cleared completely and without reliance on organ function
  - No toxic metabolites or accumulation
- Pharmacodynamic properties:
  - High oncotic effect
  - No interference with organ function (including red cell function)
  - Non-pyrogenic, non-allergenic & non-antigenic
  - No interference with haemostasis, coagulation, or acid-base balance

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
Cost	Cheap	Cheapest	Very expensive
Packaging	PVC flexible bags; long shelf life (yrs)	PVC flexible bags; long shelf life (yrs)	Glass bottles; 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)
Tonicity	Isotonic	Isotonic	Hypotonic, isooncotic
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

References

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.

[Submit a comment or correction]