An assessment of acid-base balance.

An assessment of the acid-base state of blood and, by inference, that of the body, is important in recognizing the effects of many disorders of respiratory, cardiovascular and metabolic function, in assessing their severity and in determining any necessary therapy. In making an assessment many students may now become confused for two reasons. First, the introduction of the S.I. system of units has changed much familiar terminology. Second, the recent developments in technology (Blackburn, 1978; this issue, p. 51) have led to machines generating a whole series of acid-base "indices" from, essentially, two primary measurements. These indices aim to help assess the metabolic component of any disorder, but their multiplicity might suggest that none is entirely satisfactory. The assessment presented in this paper looks at the common disorders of acid-base balance to see what pattern will be found using only the two primary measurements made in most systems—the pH and the carbon dioxide tension (Pco2). If students of acid-base balance understand these then more complex disorders will be more easily assessed. However, initially it is worthwhile emphasizing how the acid-base state of blood is regulated in the body. Knowledge of the regulation is essential for any assessment to be meaningful.