Effect of sodium-chloride ion difference on pH regulation

Background: In the Stewart approach, the difference between the cation and anion concentrations, especially between sodium, accounting for the majority of cations, and chloride, comprising the majority of anions, is an important factor in pH regulation. This study investigated the effect of sodium-chloride ion difference (SCD) on pH regulation comparing with those of PaCO2 and lactate. Methods: Arterial blood gas samples measured at our pediatric intensive care unit of a tertiary children's hospital between January and June 2020 were included. Samples that met the following criteria were excluded: samples collected from patients taking potassium bromide and samples with lactate concentration of >25 mmol/L. From the eligible data, pH was chosen as the dependent variable and SCD, lactate, and PaCO2 as independent variables, and then, a multiple regression analysis was performed. Results: In total, 5360 samples were included. Of these, five samples were excluded according to the exclusion criteria. Finally, 5355 samples were analyzed. As the variance inflation factors were <2.0 for all three variables, there was no multicollinearity. The following model was derived: pH = 7.384 + [0.97 x SCD (mEq/L) -0.66 x PaCO2 (mmHg) -1.33 x Lac (mmol/L)] x 10(-2) (adjusted R-squared = 0.73; P value < 0.001). Based on the standardized partial regression coefficients (beta), pH was affected in the order of PaCO2 (beta(PaCO2) =-0.95), SCD (beta(SCD) = 0.72), and lactate (beta(lactate) =-0.33). Conclusions: The prevention of SCD reduction, together with respiratory and metabolic management, is important for pH regulation.