PT  - JOURNAL ARTICLE
AU  - Schück, Otto
AU  - Matoušovic, Karel
TI  - RELATION BETWEEN pH AND THE STRONG ION DIFFERENCE (SID) IN BODY FLUIDS
DP  - 2005 Jul 1
TA  - Biomedical papers
PG  - 69--73
VI  - 149
IP  - 1
AID - 10.5507/bp.2005.007
IS  - 12138118
AB  - Acid-base balance evaluation according to the Henderson-Hasselbalch equation enable us to assess the contribution of respiratory (pCO&lt;sub&gt;2&lt;/sub&gt;) and/or non-respiratory (metabolic, HCO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;) 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 [HCO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;]. 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&lt;sub&gt;tot&lt;/sub&gt;]; 3. in agreement with the Henderson-Hasselbalch concept also pCO&lt;sub&gt;2&lt;/sub&gt;. 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 pCO&lt;sub&gt;2&lt;/sub&gt;, the pH of body fluids is determined by a difference between SID and [A&lt;sub&gt;tot&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;]. pH = 6.1 + log((SID - [A&lt;sub&gt;tot&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;])/(0,03*pCO&lt;sub&gt;2&lt;/sub&gt;)) or in itemized form: pH = 6.1 + log((([Na&lt;sup&gt;+&lt;/sup&gt;] + [K&lt;sup&gt;+&lt;/sup&gt;] + [Ca&lt;sup&gt;2+&lt;/sup&gt;] + [Mg&lt;sup&gt;2+&lt;/sup&gt;] - [Cl&lt;sup&gt;-&lt;/sup&gt;] - [UA&lt;sup&gt;-&lt;/sup&gt;]) - (k&lt;sub&gt;1&lt;/sub&gt;[Alb] + k&lt;sub&gt;2&lt;/sub&gt;[P&lt;sub&gt;i&lt;/sub&gt;]))/(0,03*pCO&lt;sub&gt;2&lt;/sub&gt;)) 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.