Basic Concepts of Fluid and Electrolyte Therapy

vide a simple description of the most common forms of the simple
acid-base disorders. Expert advice should be sought if it is suspected
that the patient has a more complex form of acid-base disorder.
Approaches to acid-base balance
There are essentially two different ways to approach acid-base disorders.
The traditional Schwartz-Bartter approach which accepts the
Bronsted-Lowry definition of acids as proton donors and bases as
proton acceptors. The hydrogen ion concentration is a function of
the ratio between the PCO 2
and the serum bicarbonate (as above).
The traditional approach utilises the anion gap calculation to classify
acid-base disturbances and is the method used in this chapter.
The Stewart approach, termed the Strong Ion Difference (SID), is
based on the principle that the serum bicarbonate concentration
does not alter blood pH. This approach is favoured by intensivists
and anaesthetists and is described separately towards the end of
this chapter.
Clinical presentation
It is important in every acutely ill patients to consider whether there
may be an underlying acid-base disturbance. Serum bicarbonate and
chloride are not standard components of all U&E reports and,
therefore, may have to be specifically requested. Severe acidaemia
(pH 7.6) results in irritability of cardiac and skeletal
muscle.
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