Basic Concepts of Fluid and Electrolyte Therapy

to salt and water overload, but who still have a plasma volume deficit,
as it helps draw fluid from the interstitial space into the intravascular
space and improves renal perfusion allowing excretion of excess salt
and water. Albumin is also used in patients with hepatic failure and
ascites. However, the prescription of this expensive preparation
should be confined to senior clinicians.
Although, in theory, colloids that are isooncotic with plasma should
expand the blood volume by the volume infused, in practice, the volume
expanding capacity of these colloids is only 60-80%. Never -
theless, a given volume of colloid results in greater volume expansion
and less interstitial oedema than an equivalent volume of crystalloid.
Although, in practice in the UK, we use a combination of crystalloids
and colloids for resuscitation, there is, in fact, no firm evidence that
the use of colloids rather than crystalloids in the acute phase of injury
results in better outcome.
Table 7: Volume effects of some colloids
44
Colloidal solution Duration of action Initial plasma
expanding effect (%)
Long acting
6% HES 450/0.7 24-36 h 100
6% HES 200/0.62 5-6 h 100
Medium acting
6% HES 200/0.5 3-4 h 100
10% HES 200/0.5 3-4 h 140
6% HES 130/0.40-0.42 4-6 h 100
4% Gelatin 3-4 h 90
Short acting
3% Gelatin 2-3 h 70
5% Albumin 2-4 h 70-90
HES = hydroxyethyl starch. Properties are dependent on concentration, the weightaveraged
mean molecular weight (Mw), the number-averaged molecular
weight (Mn), the molar substitution (MS) and the degree of substitution.