Smaller volumes of colloid are required for resuscitation with less contribution to oedema. Maintenance of plasma colloid osmotic pressure (COP) is a useful effect not seen with crystalloids, but colloids contain no clotting factors or other plasma enzyme systems.

Albumin is the main provider of COP and has several other roles. There is no evidence that maintaining plasma albumin levels, as opposed to plasma COP with artificial plasma substitutes, is better.

Albumin 20-25% and Pentaspan 10% are hyperoncotic and used to provide colloid where salt restriction is necessary. This is rarely necessary in intensive care as plasma volume expansion is related to the weight of colloid infused rather than the concentration. Artificial colloids used with ultrafiltration or diuresis are just as effective in oedema states.

Polygeline is a 3.5% solution containing calcium (6.25mmol/l). This prevents use of the same giving set for blood transfusions. Succinylated gelatin is a 4% solution with a larger molecular size than polygeline giving a slightly longer effect. This, and the lack of calcium in solution, make it more useful than polygeline for short term plasma volume expansion.

In patients with capillary leak albumin and smaller molecular weight colloids leak to the interstitium. In these cases it is perhaps better to use larger molecular weight colloids such as hydroxyethyl starch, though conclusive evidence is lacking.

Hetastarch and hexastarch are usually 6% solutions with a high degree of protection from metabolism due to a high degree of substitution (proportion of glucose units substituted with hydroxyethyl groups — DS) or a high ratio of C2 to C6 carbon atoms substituted (C2:C6 ratio). The molecular weight ranges vary but molecular sizes are large enough to ensure a prolonged effect. These are the most useful colloids in capillary leak. Prolonged itching related to intradermal deposition and interference with coagulation are complications if excessive doses are used.

Pentastarch and tetrastarch provide only a short term effect similar to succinylated gelatin.


0 0

Post a comment