Diagnosing acute acid-base disorders

Overview

Traditional diagnostic approach to acute acid-base disorders is based on the assessment of bicarbonate buffer system, in which pH is determined by the ratio of [HCO₃^-] to pCO₂. This, in turn, creates basis for distinguishing metabolic and respiratory disorders, and defines the term “compensation”. The use of electroneutrality advantageously complements the bicarbonate-based approach when dealing with complex acid-base disorders. It is possible to simplify this approach so it can be applied only using mental arithmetics. In principle, the space created by strong ion difference (which can be simplified to [Na⁺]-[Cl^-]) is shared by negative charges on albumin and bicarbonate. In turn, a shrinkage of this space ([Na⁺]-[Cl^-] < 32 mM) causes acidosis and an increase of [Na⁺]-[Cl^-] > 36 mM causes alka­losis, as well as a decrease in albumin concentration (for every 10 g/L of albumin, 3 mM is freed to be occupied by [HCO₃^-]). Lastly, if the sum of negative charges on albumin and [HCO₃^-] is lower than estimated strong ion difference, an unmeasured anion must be present. This concept is explained on commented case reports.

Keywords:

acid base equilibrium – electroneutrality