Comparison of three methods to estimate plasma bicarbonate in critically III patients: Henderson-Hasselbalch, enzymatic, and strong-ion-gap

Abstract

We have previously found poor agreement between Henderson-Hasselbalch and enzymatic methods for estimating plasma bicarbonate concentration in critically ill patients. In this study we compared these two established methods with a new method for estimating bicarbonate using the strong-ion-gap equation. The strong-ion-gap is derived from the Stewart approach to acid-base physiology. One hundred data sets were collected from records of routine daily blood samples in critically ill patients. Bland-Altman analyses were used to compare the three methods. We proposed that bias greater than ±1 mmol/l and limits of agreement wider than bias ±2 mmol/l were clinically important. Comparing the Henderso..