Why use crystalloids?
The advantages of crystalloid solutions are:
easy to store with long
very low incidence of
a variety of formulations
effective for use as
replacement fluids or maintenance fluids
no special compatibility
testing is required.
no religious objections to
In essence they are cheap and effective and
don't cause adverse reactions.
Crystalloids solutions are classified into
three groups (see Table 7.1) based on their predominant use. The
contents of the various solutions are listed in the table below.
These solutions are used to replace ECF. They are
all isotonic. The key factor is that these solutions have a [Na+]
similar to that of the extracellular fluid which effectively
limits their fluid distribution to the ECF. The fluid distributes
between the ISF and the plasma in proportion to their volumes.
Intracellular fluid volume does not change. If used to replace
blood loss, 3 to 4 times the volume lost must be administered
as only 1/3 to 1/4 remains intravascularly. In healthy adults with
a normal initial haemoglobin level, up to 20% loss of blood volume
(loss of approx 1,000 mls) can be safely replaced with a
3,000-4,000 ml infusion of replacement solution without any
Hartmannís solution contains lactate as a
bicarbonate precursor. The metabolism of lactate in the liver
results in production of an equivalent amount of bicarbonate.
Similarly, Plasmalyte 148 solution contains acetate and gluconate
as bicarbonate precursors. These anions (eg lactate) are the
conjugate base to the corresponding acid (eg lactic acid) and do
not contribute to development of an acidosis as they are
administered with Na+
rather than H+
as the cation.
These solutions are used to provide maintenance fluids.
They are isosmotic as administered and do not cause haemolysis.
Following administration, the glucose is rapidly taken up by cells
so the net effect is of administering pure water. Dextrose 5%
contains no Na+ so it
is distributed throughout the total body water with each
compartment receiving fluid in proportion to its contribution to
the TBW. (See Section 8.1).
Some maintenance solutions also have Na+
so they can be prescribed to provide the daily maintenance
requirements for water and Na+.
can be added as required. The normal daily Na+
intake of 1.5 to 2 mmol/kg can be given in this way by appropriate
fluid selection. The Na+
content does alter the fluid distribution but this is predictable.
Hartmannís solution contains Ca++
and this can cause problems if administered with stored blood.
Citrate is the anticoagulant used in stored blood and it works by
complexing with and removing Ca++
from solution. It is possible for the Ca++
in Hartmannís to cause clotting of blood in the infusion tubing
particularly if the blood is given slowly or the tubing contains
reservoir areas (eg as in pump sets). For this reason, it has
become standard practice to administer normal saline before and
after a blood transfusion to prevent blood and Ca++
mixing in the infusion tubing. Plasmalyte
148 solution contains Mg++ instead
of Ca++ and
can be administered with stored blood without causing this
Some crystalloid solutions used for special purposes are
grouped together here, for example:
Hypertonic (3%) saline
Half normal saline
8.4% Bicarbonate solution
All material © Copyright - Kerry Brandis, 2001