Relationship between partial carbon dioxide pressure and strong ions in humans: A retrospective study

Little is known about the role of a strong ions in humans with respiratory abnormalities. In this study, we investigated the associations between partial carbon dioxide pressure (pCO₂) and each of sodium ion (Na⁺) concentrations, chloride ion (Cl^-) concentrations and their difference (SID_Na-Cl). Blood gas data were obtained from patients in a teaching hospital intensive care unit between August 2013 and January 2017. The association between pCO₂ and SID_Na-Cl was defined as the primary outcome. The associations between pCO₂ and [Cl^-], [Na⁺] and other strong ions were secondary outcomes. pCO₂ was stratified into 10 mmHg-wide bands and treated as a categorical variable for comparison. As a result, we reviewed 115,936 blood gas data points from 3,840 different ICU stays. There were significant differences in SID_Na-Cl, [Cl^-], and [Na⁺] among all categorized pCO₂ bands. The respective pCO₂ SID_Na-Cl, [Cl^-], and [Na⁺] correlation coefficients were 0.48,-0.31, and 0.08. SID_Na-Cl increased and [Cl^-] decreased with pCO₂, with little relationship between pCO₂ and [Na⁺] across subsets. In conclusion, we found relatively strong correlations between pCO₂ and SID_Na-Cl in the multiple blood gas datasets examined. Correlations between pCO₂ and chloride concentrations, but not sodium concentrations, were further found to be moderate in these ICU data.