A critique of Stewart’s approach: the chemical mechanism of dilutional acidosis
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While Stewart’s acid-base approach is increasingly used in clinical practice, it has also led to new controversies. Acid-base disorders can be seen from different viewpoints: on the diagnostic/clinical, quantitative/mathematical, or the mechanistic level. In recent years, confusion in the interpretation and terminology of Stewart’s approach has arisen from mixing these different levels. This will be demonstrated on the basis of a detailed analysis of the mechanism of "dilutional acidosis." In the classical dilution concept, metabolic acidosis after resuscitation with large volumes is attributed to the dilution of serum bicarbonate. However, Stewart’s approach rejects this explanation and offers an alternative one that is based on a decrease in a “strong ion difference.” This mechanistic explanation is questionable for principal chemical reasons. The objective of this study is to clarify the chemical mechanism of dilutional acidosis.
Experimental data and simulations of various dilution experiments, as well as theoretical and chemical considerations were used.
1. The key to understanding the mechanism of dilutional acidosis lies in the open CO2/HCO3 −-buffer system where the buffer base (HCO3 −) is diluted whereas the buffer acid is not diluted (constant pCO2). 2. The categorization in independent and dependent variables depends on the system regarded. 3. Neither the principle of electroneutrality, nor a change in [SID], nor increased H2O dissociation plays a mechanistic role.
Stewart’s approach is valid at the mathematical level but does not provide any mechanistic insights. However, the quantification and categorization of acid-base disorders, using Stewart approach, may be helpful in clinical practice.
KeywordsVolume expansion Infusion solutions Stewart’s approach Strong ion difference Bicarbonate Acid-base
This work is dedicated to deceased Professor Roland Schmid who was our “chemical advisor” since the beginning of our acid-base scientific work. The authors would like to thank Philip D. Watson for providing his computer program “Acid-Basics II”, with which the acid-base simulations were confirmed.
- 8.Kurtz I, Kraut J, Ornekian V, Nguyen MK (2008) Acid-base analysis: a critique of the Stewart and bicarbonate-centered approaches. Am J Physiol Renal Physiol 294:F1009–F1031Google Scholar
- 15.Kellum JA, Elbers PWG (2009) Stewart’s textbook of acid-base, 2nd edn. AcidBase.org, AmsterdamGoogle Scholar
- 16.Stewart PA (1981) How to understand acid-base. A quantitative acid-base primer for biology and medicine. Elsevier, New YorkGoogle Scholar
- 22.Peters JP, Van Slyke DD (1946) Quantitative clinical chemistry: interpretations. Williams & Wilkins, BaltimoreGoogle Scholar
- 33.Watson PD (2001) Acid-Base-Calculator: AcidBasics II. Accessed 5 December 2001. http://ppn.med.sc.edu/watson/Acidbase/Acidbase.htm
- 34.Butler JN (1998) Ionic equilibrium—solubility and pH calculations. Wiley, New YorkGoogle Scholar
- 40.Zander R (2006) Bicarbonate and dilutional acidosis. In: Fluid management, Biblomed—Medizinische Verlagsgesellschaft, Melsungen, pp 13–14Google Scholar
- 41.Doberer D, Funk GC, Kneidinger N, Lindner G, Kneussl M, Schneeweiss B (2006) Base excess a universal parameter for quantification of several metabolic and respiratory acid-base disorders. Abstract, ERS Munich, GermanyGoogle Scholar
- 44.Atkins PW (1998) Physical chemistry, 6th edn. Oxford University Press, OxfordGoogle Scholar