Journal of Critical Care
Volume 25, Issue 4 , Page 654, December 2010

Comments regarding the letter “Does the complexity of the Stewart-Fencl theory allow simplification in clinical practice?”

Department of Medical Emergencies, Hospital das Clínicas,São Paulo, SP 05403-010, Brazil

published online 02 September 2010.

Article Outline

 

We read with interest the letter “Does the complexity of the Stewart-Fencl theory allow simplification in clinical practice?” and we thank the authors for their relevant comments regarding our article [1]. We agree that a great variability between different analyzers is a major limitation when comparing studies regarding acid-base disorders. This is especially true in the physicochemical approach in which important variables such as strong ion difference (SID) and strong ion gap (SIG) are not measured but calculated. Minor variations in the components of the formula may lead to great variations in the final value of the calculated variable.

The complexity of Stewart acid-base approach is by itself a major limitation for its utility in clinical practice. However, many articles have tried to make this approach more simple and then more useful at bedside [2], [3], [4]. As the authors correctly pointed out, there is an expected mathematical link between SIDai, Na+-Cl− and Cl−/Na+. This is simply explained by the fact that Na+ and Cl− are the 2 most prevalent circulating ions and the 2 great ions responsible for SIDai variations. However, instead of being a limitation, this is actually a great reason to justify the use of these simple variables (Na+-Cl− and Cl−/Na+) instead of the more time-consuming SIDai and SIG. Minimizing the variability in the Na+ and Cl− concentration between analyzers would probably be the most important measure to allow the comparison of SID and SIG values of distinct centers that study the acid-base behavior of critically ill patients.

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References 

  1. Nagaoka D, Nassar AP Jr, Maciel AT, et al. The use of sodium-chloride difference and chloride-sodium ratio as strong ion difference surrogates in the evaluation of metabolic acidosis in critically ill patients. J Crit Care 2010 doi:10.1016/j.jcrc.2010.02.003
  2. Durward A, Skellett S, Mayer A, et al. The value of the chloride: sodium ratio in differentiating the aetiology of metabolic acidosis. Intensive Care Med. 2001;27(5):828–835
  3. Boyle M, Lawrence J. An easy method of mentally estimating the metabolic component of acid/base balance using the Fencl-Stewart approach. Anaesth Intensive Care. 2003;31(5):538–547
  4. Moviat M, van Haren F, van der Hoeven H. Conventional or physicochemical approach in intensive care unit patients with metabolic acidosis. Crit Care. 2003;7(3):R41–R45

PII: S0883-9441(10)00181-4

doi:10.1016/j.jcrc.2010.07.004

Refers to article:

  • Does the complexity of the Stewart-Fencl theory allow simplification in clinical practice? , 04 October 2010

    Ba-Vinh Nguyen, Jean-Luc Carre, Catherine Guennegan, Charles C. Arvieux, Gildas Gueret
    Journal of Critical Care December 2010 (Vol. 25, Issue 4, Pages 653-654)

Journal of Critical Care
Volume 25, Issue 4 , Page 654, December 2010

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