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HOME > Acute Crit Care > Volume 40(3); 2025 > Article
Letter to the Editor
Basic science and research A simplified physicochemical approach to acid-base disorders: perioperative practical application
Acute and Critical Care 2025;40(3):509-511.
DOI: https://doi.org/10.4266/acc.001125
Published online: August 29, 2025

Division of Anesthesiology, Department of Surgery, Hospital das Clínicas de Belo Horizonte, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil

Corresponding author: Marina Ayres Delgado Division of Anesthesiology, Department of Surgery, Hospital das Clínicas de Belo Horizonte, Universidade Federal de Minas Gerais, Av Alfredo Balena 110, Santa Efigênia, Belo Horizonte, Minas Gerais 30130-100, Brasil Tel: +55-319-9957-5892 Email: marina.ayres.delgado@gmail.com
• Received: March 12, 2025   • Revised: June 24, 2025   • Accepted: July 15, 2025

© 2025 The Korean Society of Critical Care Medicine

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Dear Editor:
The understanding and management of acid-base disorders remain pivotal in the care of critically ill patients, where precision in diagnosis directly impacts therapeutic outcomes. While the traditional bicarbonate-based model has long been the cornerstone of acid-base analysis, its limitations in capturing the complexity of metabolic derangements have prompted the exploration of alternative approaches. It is within this context that we advocate for broader adoption of the Stewart method, particularly its simplified adaptation, as an indispensable tool in clinical practice [1].
The traditional model’s reliance on bicarbonate and partial pressure of carbon dioxide (PCO₂) offers a pragmatic framework for categorizing acid-base disorders. However, it often falls short in identifying nuanced imbalances, particularly those involving unmeasured ions or complex metabolic interactions. These limitations are especially evident in critically ill patients, where the interplay of multiple pathophysiological processes can obscure the root causes of acid-base disturbances. Consequently, the traditional approach may delay or misguide therapeutic interventions [1,2].
By contrast, the physicochemical model proposed by Peter Stewart provides a mechanistic understanding that transcends the oversimplifications of traditional approaches. The Stewart method offers a comprehensive framework to analyze the interplay between respiratory and metabolic components in acid-base disorders through identification of PCO₂, strong ion difference, and total concentration of weak acids [3,4]. Despite its theoretical robustness, the full Stewart model has been criticized for its mathematical complexity. To address this, David Story proposed a simplified version in 2016, adapting its application to the bedside while preserving diagnostic power. The simplified model uses practical estimations of the key variables sodium-chloride gap, albumin-corrected acid contribution, and lactate levels to identify hidden contributors to acid-base imbalances [2].
The simplified Stewart method focuses on clinically relevant variables of strong ion difference, weak acid concentration (predominantly albumin and phosphate), and PCO₂. For instance, it highlights the impact of hyperchloremic acidosis induced by saline infusions, a common yet underrecognized complication in fluid resuscitation. Similarly, it accounts for metabolic alkalosis associated with hypoalbuminemia, often observed in critically ill patients. These insights, which may be overlooked by traditional methods, enable clinicians to tailor interventions more effectively [3].
In addition, the simplified Stewart method enhances therapeutic decision-making and guides targeted interventions, such as the use of balanced crystalloid solutions to mitigate hyperchloremic acidosis or albumin supplementation to address hypoalbuminemia. Furthermore, the method’s emphasis on the role of unmeasured anions offers prognostic value, aiding in the assessment of disease severity and treatment efficacy [3].
Importantly, recent clinical evidence supports the complementary power of this simplified method in specific contexts. A prospective cohort study conducted in Brazil involving 149 patients with shock demonstrated that 13 (9%) with metabolic acidosis identified by the simplified Stewart method were not detected by the traditional model (using base excess and corrected anion gap). Furthermore, the simplified method provided a more accurate quantification of metabolic derangement, with an average underestimation of 7.8 mEq/L in base excess compared to the Stewart-derived value. These findings emphasize its diagnostic sensitivity and clinical relevance, particularly in intensive care unit (ICU) settings [5].
Additional studies corroborate these findings. Martin et al. [6] showed that the physicochemical method reclassified the nature of acid-base disorders in a significant proportion of trauma ICU patients, with potential implications for mortality risk stratification. Similarly, Szrama and Smuszkiewicz [7] reported that the Stewart approach improved etiologic understanding in septic patients, often uncovering abnormalities masked in traditional evaluations.
Moreover, the method’s emphasis on unmeasured anions—including phosphate, sulfate, and organic acids—provides a more complete picture of metabolic disturbances. In our institutional experience—particularly in high-complexity perioperative settings such as liver transplantation and cardiac surgery—the simplified Stewart approach has demonstrated greater sensitivity. This allows targeted therapeutic strategies, such as switching from saline to balanced crystalloids in hyperchloremic acidosis or considering albumin replacement in hypoalbuminemic alkalosis [6].
While some clinicians perceive the Stewart approach as a theoretical replacement for conventional analysis, we argue that its simplified form serves as a valuable complementary tool. It bridges the gap between physiology and bedside decision-making, enhancing the clinician’s ability to act decisively in the face of complex acid-base challenges [2].
In conclusion, the simplified Stewart method represents a meaningful advancement in acid-base assessment. Its growing use in critical care, anesthesia, and perioperative medicine reflects not only its theoretical robustness but also its practical relevance. Integrating this approach into routine practice may improve diagnostic accuracy, guide tailored interventions, and ultimately contribute to better patient outcomes.

CONFLICT OF INTEREST

No potential conflict of interest relevant to this article was reported.

FUNDING

None.

ACKNOWLEDGMENTS

None.

AUTHOR CONTRIBUTIONS

Conceptualization: VTG, MAD. Methodology: MAD. Formal analysis: LMV, MAD. Data curation: MAD. Visualization: GHR, MAD. Project administration: VTG, MAD. Funding acquisition: MAD. Writing - original draft: GHR, MAD. Writing - review & editing: LMV, MAD. All authors read and agreed to the published version of the manuscript.

  • 1. Gomez H, Kellum JA. Understanding acid base disorders. Crit Care Clin 2015;31:849-60.ArticlePubMed
  • 2. Magder S, Emami A. Practical approach to physical-chemical acid-base management: Stewart at the bedside. Ann Am Thorac Soc 2015;12:111-7.ArticlePubMed
  • 3. Story DA. Stewart acid-base: a simplified bedside approach. Anesth Analg 2016;123:511-5.ArticlePubMed
  • 4. Kellum JA. Determinants of plasma acid-base balance. Crit Care Clin 2005;21:329-46.ArticlePubMed
  • 5. Dos Passos MG, Blaya LB, Boniatti MM. Comparison of a modified Story approach to traditional evaluation of acid-base disturbances in patients with shock: a cohort study. J Clin Monit Comput 2022;36:817-22.ArticlePubMedPDF
  • 6. Martin M, Murray J, Berne T, Demetriades D, Belzberg H. Diagnosis of acid-base derangements and mortality prediction in the trauma intensive care unit: the physiochemical approach. J Trauma 2005;58:238-43.ArticlePubMed
  • 7. Szrama J, Smuszkiewicz P. An acid-base disorders analysis with the use of the Stewart approach in patients with sepsis treated in an intensive care unit. Anaesthesiol Intensive Ther 2016;48:180-4.ArticlePubMed

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        A simplified physicochemical approach to acid-base disorders: perioperative practical application
        Acute Crit Care. 2025;40(3):509-511.   Published online August 29, 2025
        DOI: https://doi.org/10.4266/acc.001125
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      A simplified physicochemical approach to acid-base disorders: perioperative practical application
      A simplified physicochemical approach to acid-base disorders: perioperative practical application
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