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

A bstract 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. Conclusion 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. How to cite this article Paliwal R, Pakavakis A, Divatia JV, Kulkarni AP. 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. Indian J Crit Care Med 2022;26(1):23–32.

Acid–Base Analysis in the Operating Room: A Bedside Stewart Approach

“…In contrast, bicarbonate-based approaches cannot easily explain this inverse relationship between plasma albumin and bicarbonate despite advocates recommending correcting the anion gap for decreased albumin. 10 Further, studies of ICU patients, including postoperative patients, conclude that the Stewart approach can be superior in detecting important acid-base changes despite patient pH being in the reference range (7.35 to 7.45) [11][12][13] and no apparent acid-base disorder using bicarbonate or base excess analysis (example 4 in Box 4). In this review focusing on clinical anesthesia, I am proposing a simplified Stewart approach that incorporates base excess because it is associated with greater insight into the underlying causes including some masked by other processes.…”