Abstract
Acid-base balance evaluation according to the Henderson-Hasselbalch equation enable us to assess the contribution of respiratory (pCO2) and/or non-respiratory (metabolic, HCO3(-)) components to the acid-base balance status. A new approach to acid-base balance evaluation according to Stewart-Fencl, which is based on a detailed physical-chemical analysis of body fluids shows that metabolic acid-base balance disorders are characterized not only by [HCO3(-)]. According to this concept independent variables must be taken into an account. The abnormality of concentration of one or more of the independent variable(s) determines the pH of a solution. The independent variables are: 1. strong ion difference (SID); 2. total concentration of nonvolatile weak acids [A(tot)]; 3. in agreement with the Henderson-Hasselbalch concept also pCO2. Traditional evaluation of acid-base balance disorders is based on the pH of body fluids (though pH may be within normal range if several acid-base balance disturbances are present). In order to maintain this view and simultaneously to respect the Stewart-Fencl principle, we invented a new equation, which uses only the independent variables to define the pH of body fluids. This analysis shows that for a given value of pCO2, the pH of body fluids is determined by a difference between SID and [A(tot)-]. pH = 6.1 + log((SID - [A(tot)-])/(0.03pCO2)) or in itemized form: pH = 6.1 + log((([Na+] + [K+] + [Ca2+] + [Mg2+] - [Cl-] - [UA-]) - (k1[Alb] + k2[P(i)]))/(0.03 x pCO2)). Evaluation of the individual components of this equation enables us to detect, which of the independent variable (or a combination of independent variables) deviates from the normal range and therefore which one or ones is a cause of the acid-base balance disorder. At the end of this paper we give examples of a practical application of this equation.
Highlights
Acid-base balance evaluation according to the Henderson-Hasselbalch equation enable us to assess the contribution of respiratory and/or non-respiratory components to the acid-base balance status
Evaluation of the individual components of this equation enables us to detect, which of the independent variable deviates from the normal range and which one or ones is a cause of the acid-base balance disorder
The acid-base status of body fluids is traditionally assessed according to the variables in the Henderson-Hasselbalch equation
Summary
Acid-base balance evaluation according to the Henderson-Hasselbalch equation enable us to assess the contribution of respiratory (pCO2) and/or non-respiratory (metabolic, HCO3–) components to the acid-base balance status. On the basis of a detailed physical-chemical analysis of body fluids, Stewart defined two independent variables that enable us to define metabolic disturbances of the acid-base balance exactly a) strong ion difference – SID b) total concentrations of the weak non-volatile acids ([Atot], represented mainly by albumin and inorganic phosphate) Respiratory acid-base balance disturbances are assessed according to pCO2, in the same way as in a conventional approach.
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