Utility of Stewart’s Approach to Diagnose Missed Complex Acid-base Disorders as Compared to Bicarbonate-anion Gap Based Methodology in Critically Ill Patients: An Observational Study

Abstract

Background: Traditional arterial blood gas (ABG) analysis may miss out on some metabolic acid-base disorders. We prospectively compared Stewart’s approach in critically ill patients to traditional bicarbonate—anion gap-based methods (with and without correction for albumin) to diagnose acid-base disorders. Patients and methods: Five hundred ABG samples from medical or surgical patients in the ICU were analyzed with traditional bicarbonate—anion gap-based methodology with and without correction for albumin and Stewart’s biochemical approach. The primary outcome identification of additional metabolic disorders diagnosed with Stewart’s approach in comparison to bicarbonate system-based approaches. We also looked at the correlation between the strong ion gap (SIG) and the albumin corrected anion gap (acAnion Gap). Results: Stewart’s approach detected missed metabolic disorders in 58 (11.6%) blood gas results reported as “within normal limits” with the bicarbonate-uncorrected anion gap approach. In 50 (10%) of these ABGs, the acAnion Gap approach was able to diagnose the missed metabolic disorders. Thus, the albumin-corrected anion gap method had a similar diagnostic performance to Stewart’s approach, as it missed additional disorders in only eight (1.6%) blood gases. Conclusions: In this study, we found that the acAnion Gap approach was similar in diagnostic performance to Stewart’s approach. We feel that the corrected anion gap approach can be safely used if a ready calculator for Stewart’s approach is not available.