Modern quantitative acid–base chemistry

Abstract

Quantitative analysis of ionic solutions in terms of physical and chemical principles has been effectively prohibited in the past by the overwhelming amount of calculation it required, but computers have suddenly eliminated that prohibition. The result is an approach to acid-base which revolutionizes our ability to understand, predict, and control what happens to hydrogen ions in living systems. This review outlines that approach and suggests some of its most useful implications. Quantitative understanding requires distinctions between independent variables (in body fluids: pCO2, net strong ion charge, and total weak acid, usually protein), and dependent variables [( HCO-3], [HA], [A-], [CO(2-)3], [OH-], and [H+] (or pH]. Dependent variables are determined by independent variables, and can be calculated from the defining equations for the specific system. Hydrogen ion movements between solutions can not affect hydrogen ion concentration; only changes in independent variables can. Many current models for ion movements through membranes will require modification on the basis of this quantitative analysis. Whole body acid-base balance can be understood quantitatively in terms of the three independent variables and their physiological regulation by the lungs, kidneys, gut, and liver. Quantitative analysis also shows that body fluids interact mainly by strong ion movements through the membranes separating them.

The use of elements of the Stewart model (Strong Ion Approach) for the diagnostics of respiratory acidosis on the basis of the calculation of a value of a modified anion gap (AGm) in brachycephalic dogs

“…Apart from the HH equation, the acid-base balance of an organism is also described by the Stewart model (Stewart 1978(Stewart , 1983. According to this theory, which is called the Strong Ion Approach, the ions in the blood serum can be divided into two groups -nonbuffer ions and buffer ions.…”

Role of pump prime in the etiology of cardio-pulmonary bypass associated acidosis

“…The importance of hyperchloremia is emphasized by Stewart's mathematically based approach to acid base balance (5). According to Stewart, the major determinant of hydrogen ion concentration is the strong ion difference (SID) in the body.…”

Physicochemical Approach to Determine the Mechanism for Acid–Base Disorders in 793 Hospitalized Foals

“…SID has 2 components: measured strong ion difference (SID m ), which was calculated from the measured plasma concentrations of 3 strong ions (Na + , K + , Cl − ) as:18 ${\text{SID}}_{\mathrm{normalm}}=\text{Na}+\mathrm{K}-\text{Cl}$ …”

“…Neither the base excess nor the bicarbonate can explain the cause of a disturbance, only its existence and severity 16, 17. The quantitative physicochemical approach emphasizes the importance of strong ion difference (SID) which is the difference between the charge of plasma strong cations (Na + , K + ,Ca 2+ , Mg 2+ and anions (Cl − , l ‐lactate − , sulfate, and ketoacids), p a CO 2 , and total plasma protein concentration ( A tot ) in determining plasma pH and [${\text{HCO}}_3^{-}$] 18, 19. This approach is mechanistic and provides a more in‐depth insight into the pathophysiology of acid–base imbalances 18.…”

“…The quantitative physicochemical approach emphasizes the importance of strong ion difference (SID) which is the difference between the charge of plasma strong cations (Na + , K + ,Ca 2+ , Mg 2+ and anions (Cl − , l ‐lactate − , sulfate, and ketoacids), p a CO 2 , and total plasma protein concentration ( A tot ) in determining plasma pH and [${\text{HCO}}_3^{-}$] 18, 19. This approach is mechanistic and provides a more in‐depth insight into the pathophysiology of acid–base imbalances 18. The mechanisms responsible for local, regional, and systemic acid–base are incompletely understood and controversy exists in the literature as to what method should be used 20.…”