Independent variables of pH: Ten Knights of the Hydrogen Ion Kingdom-Part I. A prospective observational study

by Bulent Gucyetmez, Kaan Gucyetmez, Zeynep Tugce Sarikaya, Lutfi Telci

CO₂, HCO₃, SID_, and total weak acids have been defined as pH’s independent variables. However, according to Gamble, HCO₃ should be equal to the difference between the sum of cations and the sum of anions besides HCO₃. Therefore, if this mathematical expression is substituted for HCO₃ in the Henderson-Hasselbalch equation, all independent variables of pH can be demonstrated. Our aim is to test this theory in this study. This prospective observational study was conducted between 2019 and 2020. All admitted patients to the intensive care unit who were >18 years old were included. Demographic data, blood gas parameters, albumin, magnesium, and inorganic phosphorus levels, and outcomes were recorded twice (at admission and at the 24^th hour). The multivariate linear regression model was used to determine pH’s independent variables. In the multivariate linear regression model, pH was significantly increased by each unit increase in Na, K, Ca, and Mg (mmol L^-1). In contrast, pH was significantly decreased by each unit increase in CO₂, Cl, lactate, albumin (g dL^-1), inorganic phosphorus (mg dL^-1), and the strong ion gap. Ten independent variables can accurately predict the changes in pH. For this reason, all ten independent variables should be separately evaluated when interpreting the acid-base status. With this understanding, all algorithms regarding acid-base evaluation may become unnecessary.