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Ježek F, Kofránek J. Modern and traditional approaches combined into an effective gray-box mathematical model of full-blood acid-base. Theor Biol Med Model 2018; 15:14. [PMID: 30196793 PMCID: PMC6130067 DOI: 10.1186/s12976-018-0086-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2018] [Accepted: 07/24/2018] [Indexed: 12/02/2022] Open
Abstract
Background The acidity of human body fluids, expressed by the pH, is physiologically regulated in a narrow range, which is required for the proper function of cellular metabolism. Acid-base disorders are common especially in intensive care, and the acid-base status is one of the vital clinical signs for the patient management. Because acid-base balance is connected to many bodily processes and regulations, complex mathematical models are needed to get insight into the mixed disorders and to act accordingly. The goal of this study is to develop a full-blood acid-base model, designed to be further integrated into more complex human physiology models. Results We have developed computationally simple and robust full-blood model, yet thorough enough to cover most of the common pathologies. Thanks to its simplicity and usage of Modelica language, it is suitable to be embedded within more elaborate systems. We achieved the simplification by a combination of behavioral Siggaard-Andersen’s traditional approach for erythrocyte modeling and the mechanistic Stewart’s physicochemical approach for plasma modeling. The resulting model is capable of providing variations in arterial pCO2, base excess, strong ion difference, hematocrit, plasma protein, phosphates and hemodilution/hemoconcentration, but insensitive to DPG and CO concentrations. Conclusions This study presents a straightforward unification of Siggaard-Andersen’s and Stewart’s acid-base models. The resulting full-blood acid-base model is designed to be a core part of a complex dynamic whole-body acid-base and gas transfer model. Electronic supplementary material The online version of this article (10.1186/s12976-018-0086-9) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Filip Ježek
- Department of Cybernetics, Faculty of Electrical Engineering, Czech Technical University in Prague, Prague, Czech Republic. .,Institute of Pathological Physiology, First Faculty of Medicine, Charles University, U nemocnice 5, 128 00, Prague 2, Czech Republic.
| | - Jiří Kofránek
- Institute of Pathological Physiology, First Faculty of Medicine, Charles University, U nemocnice 5, 128 00, Prague 2, Czech Republic
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Omron EM. Comparative Quantitative Acid-Base Analysis in Coronary Artery Bypass, Severe Sepsis, and Diabetic Ketoacidosis. J Intensive Care Med 2016; 20:317-26. [PMID: 16280404 DOI: 10.1177/0885066605279955] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The main objective of this study was to assess the relationship of standard base excess (SBE) to delta strong ion difference effective (ΔSIDe) in critical illness. Critical illness is characterized by variable plasma nonvolatile weak acid components (ΔA-), and SBE becomes discordant with ΔSIDe. The author hypothesized that both acid-base models are equivalent when SBE and ΔSIDe are corrected for ΔA-. A retrospective chart review was performed to assess this hypothesis by looking at changes in SBE, ΔSIDe, and ΔA-in 30 coronary artery bypass graft surgery patients, 30 severe sepsis patients, and 15 diabetic ketoacidosis patients. SBE equals the sum of the ΔSIDe and ΔA-. The SBE quantifies the magnitude of the metabolic acid-base derangement, the ΔSIDe quantifies the plasma strong cation/anion imbalance, and the ΔA-quantifies the magnitude of the hypoalbuminemic alkalosis. The partitioning of SBE into physicochemical components can facilitate analyses of complex acid-base disorders in critical illness.
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Affiliation(s)
- Edward M Omron
- Division of Pulmonary Medicine, National Naval Medical Center, Bethesda, MD, USA.
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Fores-Novales B, Diez-Fores P, Aguilera-Celorrio LJ. Assessment of acid-base balance. Stewart's approach. REVISTA ESPANOLA DE ANESTESIOLOGIA Y REANIMACION 2016; 63:212-219. [PMID: 26143339 DOI: 10.1016/j.redar.2015.04.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 03/19/2015] [Accepted: 04/13/2015] [Indexed: 06/04/2023]
Abstract
The study of acid-base equilibrium, its regulation and its interpretation have been a source of debate since the beginning of 20th century. Most accepted and commonly used analyses are based on pH, a notion first introduced by Sorensen in 1909, and on the Henderson-Hasselbalch equation (1916). Since then new concepts have been development in order to complete and make easier the understanding of acid-base disorders. In the early 1980's Peter Stewart brought the traditional interpretation of acid-base disturbances into question and proposed a new method. This innovative approach seems more suitable for studying acid-base abnormalities in critically ill patients. The aim of this paper is to update acid-base concepts, methods, limitations and applications.
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Affiliation(s)
- B Fores-Novales
- Servicio de Anestesiología y Reanimación, Hospital Universitario Basurto, Bilbao, España; Departamento de Cirugía, Radiología y Medicina Física, Facultad de Medicina y Odontología, Universidad del País Vasco, Leioa, España.
| | - P Diez-Fores
- Servicio de Anestesiología y Reanimación, Hospital Universitario Basurto, Bilbao, España; Departamento de Cirugía, Radiología y Medicina Física, Facultad de Medicina y Odontología, Universidad del País Vasco, Leioa, España
| | - L J Aguilera-Celorrio
- Servicio de Anestesiología y Reanimación, Hospital Universitario Basurto, Bilbao, España; Departamento de Cirugía, Radiología y Medicina Física, Facultad de Medicina y Odontología, Universidad del País Vasco, Leioa, España
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The base excess gap is not a valid tool for the quantification of unmeasured ions in cardiac surgical patients: a retrospective observational study. Eur J Anaesthesiol 2014; 30:678-84. [PMID: 23867780 DOI: 10.1097/eja.0b013e32836412db] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND The base excess gap (BE(gap)) method is commonly used for the quantification of unmeasured ions in critically ill patients. However, it has never been validated against the standard quantitative acid-base approach. OBJECTIVE To compare the BE(gap) as a tool for the prediction of the excess of unmeasured ions with the offset of strong ion gap (SIG) from its reference value. DESIGN A retrospective observational study. SETTING Adult ICU in a tertiary hospital. PATIENTS One hundred and thirty-five cardiac surgical patients admitted for postoperative care. INTERVENTIONS None. MAIN OUTCOME MEASURES BE(gap) was calculated as BE(gap) = SBE - BE(si) - BE(wa), where SBE is the standard base excess, BE(si) is the partition due to strong ions ([Na+]-[Cl-]-[lactate-] - 30.5) and BE(wa) is the partition due to weak acids [0.25×{42 - (albumin)}]. The deviation of the observed SIG (SIG(ob)) from its reference value was calculated as deltaSIG = 2.85 - SIG(ob). We used Bland-Altman and concordance correlation analysis to compare BE(gap) with deltaSIG. A bias of ±1 meq l(-1) with limits of agreement of ±2 meq l(-1) and a concordant correlation coefficient of more than 0.9 were considered to indicate a strong agreement. RESULTS The concordant correlation coefficient between BE(gap) and deltaSIG was 0.702. The mean bias between the two variables was 1.8 meq l(-1), with a lower limit of agreement of -0.9 meq l(-1) and an upper limit of agreement of 4.4 meq l(-1). CONCLUSION The BE gap method cannot reliably quantify the unmeasured ion excess in cardiac surgical patients. Clinicians should use the full Stewart-Figge model for quantitative acid-base assessments.
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Lindinger MI, Heigenhauser GJF. Counterpoint: Lactic acid is not the only physicochemical contributor to the acidosis of exercise. J Appl Physiol (1985) 2008; 105:359-61; discussion 361-2. [DOI: 10.1152/japplphysiol.00162.2008a] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Kurtz I, Kraut J, Ornekian V, Nguyen MK. Acid-base analysis: a critique of the Stewart and bicarbonate-centered approaches. Am J Physiol Renal Physiol 2008; 294:F1009-31. [PMID: 18184741 DOI: 10.1152/ajprenal.00475.2007] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
When approaching the analysis of disorders of acid-base balance, physical chemists, physiologists, and clinicians, tend to focus on different aspects of the relevant phenomenology. The physical chemist focuses on a quantitative understanding of proton hydration and aqueous proton transfer reactions that alter the acidity of a given solution. The physiologist focuses on molecular, cellular, and whole organ transport processes that modulate the acidity of a given body fluid compartment. The clinician emphasizes the diagnosis, clinical causes, and most appropriate treatment of acid-base disturbances. Historically, two different conceptual frameworks have evolved among clinicians and physiologists for interpreting acid-base phenomena. The traditional or bicarbonate-centered framework relies quantitatively on the Henderson-Hasselbalch equation, whereas the Stewart or strong ion approach utilizes either the original Stewart equation or its simplified version derived by Constable. In this review, the concepts underlying the bicarbonate-centered and Stewart formulations are analyzed in detail, emphasizing the differences in how each approach characterizes acid-base phenomenology at the molecular level, tissue level, and in the clinical realm. A quantitative comparison of the equations that are currently used in the literature to calculate H+concentration ([H+]) is included to clear up some of the misconceptions that currently exist in this area. Our analysis demonstrates that while the principle of electroneutrality plays a central role in the strong ion formulation, electroneutrality mechanistically does not dictate a specific [H+], and the strong ion and bicarbonate-centered approaches are quantitatively identical even in the presence of nonbicarbonate buffers. Finally, our analysis indicates that the bicarbonate-centered approach utilizing the Henderson-Hasselbalch equation is a mechanistic formulation that reflects the underlying acid-base phenomenology.
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Morris CG, Low J. Metabolic acidosis in the critically ill: Part 1. Classification and pathophysiology. Anaesthesia 2008; 63:294-301. [DOI: 10.1111/j.1365-2044.2007.05370.x] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Dubin A, Menises MM, Masevicius FD, Moseinco MC, Kutscherauer DO, Ventrice E, Laffaire E, Estenssoro E. Comparison of three different methods of evaluation of metabolic acid-base disorders. Crit Care Med 2007; 35:1264-70. [PMID: 17334252 DOI: 10.1097/01.ccm.0000259536.11943.90] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVES The Stewart approach states that pH is primarily determined by Pco2, strong ion difference (SID), and nonvolatile weak acids. This method might identify severe metabolic disturbances that go undetected by traditional analysis. Our goal was to compare diagnostic and prognostic performances of the Stewart approach with a) the traditional analysis based on bicarbonate (HCO3) and base excess (BE); and b) an approach relying on HCO3, BE, and albumin-corrected anion gap (AGcorrected). DESIGN Prospective observational study. SETTING A university-affiliated hospital intensive care unit (ICU). PATIENTS Nine hundred thirty-five patients admitted to the ICU. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS The Stewart approach detected an arterial metabolic alteration in 131 (14%) of patients with normal HCO3- and BE, including 120 (92%) patients with metabolic acidosis. However, 108 (90%) of these patients had an increased AGcorrected. The Stewart approach permitted the additional diagnosis of metabolic acidosis in only 12 (1%) patients with normal HCO3, BE, and AGcorrected. On the other hand, the Stewart approach failed to identify 27 (3%) patients with alterations otherwise observed with the use of HCO3-, BE, and AGcorrected (16 cases of acidosis and 11 of alkalosis). SID and BE, and strong ion gap (SIG) and AGcorrected, were tightly correlated (R2 = .86 and .97, p < .0001 for both) with narrow 95% limits of agreement (8 and 3 mmol/L, respectively). Areas under receiver operating characteristic curves to predict 30-day mortality were 0.83, 0.62, 0.61, 0.60, 0.57, 0.56, and 0.67 for Sepsis-related Organ Failure Assessment (SOFA) score, SIG, AGcorrected, SID, BE, HCO3-, and lactates, respectively (SOFA vs. the rest, p < .0001). CONCLUSIONS In this large group of critically ill patients, diagnostic performance of the Stewart approach exceeded that of HCO3- and BE. However, when AGcorrected was included in the analysis, the Stewart approach did not offer any diagnostic or prognostic advantages.
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Affiliation(s)
- Arnaldo Dubin
- Servicio de Terapia Intensiva, Sanatorio Otamendi y Miroli, Buenos Aires, Argentina.
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Quintard H, Hubert S, Ichai C. Qu'apporte le modèle de Stewart à l'interprétation des troubles de l'équilibre acide–base? ACTA ACUST UNITED AC 2007; 26:423-33. [PMID: 17462852 DOI: 10.1016/j.annfar.2007.02.012] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2006] [Accepted: 02/10/2007] [Indexed: 11/24/2022]
Abstract
OBJECTIVES To explain the different approaches for interpreting acid-base disorders; to develop the Stewart model which offers some advantages for the pathophysiological understanding and the clinical interpretation of acid-base imbalances. DATA SOURCE Record of french and english references from Medline data base. The keywords were: acid-base balance, hyperchloremic acidosis, metabolic acidosis, strong ion difference, strong ion gap. DATA EXTRACTION Data were selected including prospective and retrospective studies, reviews, and case reports. DATA SYNTHESIS Acid-base disorders are commonly analysed by using the traditional Henderson-Hasselbalch approach which attributes the variations in plasma pH to the modifications in plasma bicarbonates or PaCO2. However, this approach seems to be inadequate because bicarbonates and PaCO2 are completely dependent. Moreover, it does not consider the role of weak acids such as albuminate, in the determination of plasma pH value. According to the Stewart concept, plasma pH results from the degree of plasma water dissociation which is determined by 3 independent variables: 1) strong ion difference (SID) which is the difference between all the strong plasma cations and anions; 2) quantity of plasma weak acids; 3) PaCO2. Thus, metabolic acid-base disorders are always induced by a variation in SID (decreased in acidosis) or in weak acids (increased in acidosis), whereas respiratory disorders remains the consequence of a change in PaCO2. These pathophysiological considerations are important to analyse complex acid-base imbalances in critically ill patients. For example, due to a decrease in weak acids, hypoalbuminemia increases SID which may counter-balance a decrease in pH and an elevated anion gap. Thus if using only traditional tools, hypoalbuminemia may mask a metabolic acidosis, because of a normal pH and a normal anion gap. In this case, the association of metabolic acidosis and alkalosis is only expressed by respectively a decreased SID and a decreased weak acids concentration. This concept allows to establish the relationship between hyperchloremic acidosis and infusion of solutes which contain large concentration of chloride such as NaCl 0.9%. Finally, the Stewart concept permits to understand that sodium bicarbonate as well as sodium lactate induces plasma alkalinization. In fact, sodium remains in plasma, whereas anion (lactate or bicarbonate) are metabolized leading to an increase in plasma SID. CONCLUSION Due to its simplicity, the traditional Henderson-Hasselbalch approach of acid-base disorders, remains commonly used. However, it gives an inadequate pathophysiological analysis which may conduct to a false diagnosis, especially with complex acid-base imbalances. Despite its apparent complexity, the Stewart concept permits to understand precisely the mechanisms of acid-base disorders. It has to become the most appropriate approach to analyse complex acid-base abnormalities.
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Affiliation(s)
- H Quintard
- Service de réanimation médicochirugicale, département d'anesthesie-réanimation Est, hôpital Saint-Roch, 5, rue Pierre-Dévoluy, CHU de Nice, 06006 Nice cedex 01, France
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10
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Dascombe BJ, Reaburn PRJ, Sirotic AC, Coutts AJ. The reliability of the i-STAT clinical portable analyser. J Sci Med Sport 2006; 10:135-40. [PMID: 16846754 DOI: 10.1016/j.jsams.2006.05.023] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Revised: 05/26/2006] [Accepted: 05/31/2006] [Indexed: 11/28/2022]
Abstract
The purpose of this investigation was to assess the reliability of the i-STAT clinical portable analyser and CG(4)(+) cartridge measures of blood pH, partial pressures of O(2) (pO(2)) and CO(2) (pCO(2)), bicarbonate ([HCO(3)(-)]), base excess (BE), total carbon dioxide (TCO(2)), oxygen saturation (sO(2)) and blood lactate ([BLa(-)]) at various exercise intensities. A comparison between [BLa(-)] measured by the i-STAT and the Accusport lactate analysers during an intermittent treadmill run was also undertaken. The technical error of measurement (TEM%) at rest, at moderate (200W) and maximal exercise (V O(2)max) was acceptable (<15%) for all parameters. The intra-class correlation coefficients for each analyte ranged from weak-to-strong across resting (ICC=0.19-0.96) and moderate (ICC=0.30-0.96) exercise intensities. The ICC for all analytes were observed to be strong following maximal intensity exercise (ICC=0.77-0.95). The comparison of the [BLa(-)] measures between the i-STAT and Accusport showed that the difference between measures was acceptable at both low (<4mmolL(-1)) (-0.39+/-0.27mmolL(-1)), moderate to high concentrations (>4mmolL(-1)) (0.58+/-1.22mmolL(-1)), and across all [BLa(-)] data (0.36+/-1.13mmolL(-1)). In conclusion, the i-STAT clinical analyser and CG(4)(+) cartridge provides reliable measures of a number of blood parameters across exercise intensities. The [BLa(-)] measures from the i-STAT analyser are consistent with that of the Accusport lactate analyser.
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Affiliation(s)
- B J Dascombe
- School of Health and Human Performance, Faculty of Science, Engineering and Health, Central Queensland University, North Rockhampton, Qld, Australia.
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11
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Schück O, Matoušovic K. RELATION BETWEEN pH AND THE STRONG ION DIFFERENCE (SID) IN BODY FLUIDS. Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub 2005. [DOI: 10.5507/bp.2005.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Anstey CM. Comparison of three strong ion models used for quantifying the acid-base status of human plasma with special emphasis on the plasma weak acids. J Appl Physiol (1985) 2005; 98:2119-25. [PMID: 15677731 DOI: 10.1152/japplphysiol.01286.2004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Currently, three strong ion models exist for the determination of plasma pH. Mathematically, they vary in their treatment of weak acids, and this study was designed to determine whether any significant differences exist in the simulated performance of these models. The models were subjected to a "metabolic" stress either in the form of variable strong ion difference and fixed weak acid effect, or vice versa, and compared over the range 25 < or = Pco(2) < or = 135 Torr. The predictive equations for each model were iteratively solved for pH at each Pco(2) step, and the results were plotted as a series of log(Pco(2))-pH titration curves. The results were analyzed for linearity by using ordinary least squares regression and for collinearity by using correlation. In every case, the results revealed a linear relationship between log(Pco(2)) and pH over the range 6.8 < or = pH < or = 7.8, and no significant difference between the curve predictions under metabolic stress. The curves were statistically collinear. Ultimately, their clinical utility will be determined both by acceptance of the strong ion framework for describing acid-base physiology and by the ease of measurement of the independent model parameters.
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Affiliation(s)
- Chris M Anstey
- Intensive Care, Dept. of Intensive Care, Nambour Hospital, Nambour, Queensland 4560, Australia.
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Abstract
There has been renewed interest in quantifying acid-base disorders in the intensive care unit. One of the methods that has become increasingly used to calculate acid-base balance is the Stewart model. This model is briefly discussed in terms of its origin, its relationship to other methods such as the base excess approach, and the information it provides for the assessment and treatment of acid-base disorders in critically ill patients.
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Wooten EW. Calculation of physiological acid-base parameters in multicompartment systems with application to human blood. J Appl Physiol (1985) 2003; 95:2333-44. [PMID: 12923118 DOI: 10.1152/japplphysiol.00560.2003] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A general formalism for calculating parameters describing physiological acid-base balance in single compartments is extended to multicompartment systems and demonstrated for the multicompartment example of human whole blood. Expressions for total titratable base, strong ion difference, change in total titratable base, change in strong ion difference, and change in Van Slyke standard bicarbonate are derived, giving calculated values in agreement with experimental data. The equations for multicompartment systems are found to have the same mathematical interrelationships as those for single compartments, and the relationship of the present formalism to the traditional form of the Van Slyke equation is also demonstrated. The multicompartment model brings the strong ion difference theory to the same quantitative level as the base excess method.
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Affiliation(s)
- E Wrenn Wooten
- Department of Radiology, Baylor University Medical Center, Dallas, Texas 75246, USA
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Morgan TJ, Venkatesh B. Strong Ions, Acid-base, and Crystalloid Design. Intensive Care Med 2002. [DOI: 10.1007/978-1-4757-5551-0_39] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Abstract
Acid-base homeostasis is an important determinant of many physiologic functions. Nowhere is understanding the mechanisms and significance of hydrogen ion (H+) imbalance more important than in critical care management, where patients are threatened with a physiochemical disorder that is often as complex as it is dangerous. Although there may be contentious issues yet unresolved concerning acid-base homeostasis, the incontrovertible fact is that the body at least seems to defend H+ balance as vigorously as it does oxygen transport or perfusion pressure. Equally, there seems to be an important and predictable relation between this balance and other physiochemical variables such as concentrations of other ionic species, carbon dioxide, and plasma proteins. The prudent clinician strives to understand whether or not and how acid-base imbalances are affecting his or her patient and what to do about it.
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Affiliation(s)
- J M Rubash
- Animal Emergency Clinic Southeast, Houston, Texas, USA.
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Fencl V, Jabor A, Kazda A, Figge J. Diagnosis of metabolic acid-base disturbances in critically ill patients. Am J Respir Crit Care Med 2000; 162:2246-51. [PMID: 11112147 DOI: 10.1164/ajrccm.162.6.9904099] [Citation(s) in RCA: 248] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
We compare two commonly used diagnostic approaches, one relying on plasma bicarbonate concentration and "anion gap," the other on "base excess," with a third method based on physicochemical principles, for their value in detecting complex metabolic acid-base disturbances. We analyzed arterial blood samples from 152 patients and nine normal subjects for pH, PCO(2), and concentrations of plasma electrolytes and proteins. Ninety-six percent of the patients had serum albumin concentration < or = 3 SD below the mean of the control subjects. In about one-sixth of the patients, base excess and plasma bicarbonate were normal. In a great majority of these apparently normal samples, the third method detected simultaneous presence of acidifying and alkalinizing disturbances, many of them grave. The almost ubiquitous hypoalbuminemia confounded the interpretation of acid-base data when the customary approaches were applied. Base excess missed serious acid-base abnormalities in about one-sixth of the patients; this method fails when the plasma concentrations of the nonbicarbonate buffers (mainly albumin) are abnormal. Anion gap detected a hidden "gap acidosis" in only 31% of those samples with normal plasma bicarbonate in which such acidosis was diagnosed by the third method; when adjusted for hypoalbuminemia, it reliably detected the hidden abnormal anions. The proposed third method identifies and quantifies individual components of complex acid-base abnormalities and provides insights in their pathogenesis.
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Affiliation(s)
- V Fencl
- Division of Pulmonary and Critical Care Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115-6110, USA.
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Abstract
The adequacy of intestinal perfusion during shock and resuscitation might be estimated from intestinal tissue acid-base balance. We examined this idea from the perspective of conventional blood acid-base physicochemistry. As the O(2) supply diminishes with failing blood flow, tissue acid-base changes are first "respiratory, " with CO(2) coming from combustion of fuel and stagnating in the decreasing blood flow. When the O(2) supply decreases to critical, the changes become "metabolic" due to lactic acid. In blood, the respiratory vs. metabolic distinction is conventionally made using the buffer base principle, in which buffer base is the sum of HCO(3)(-) and noncarbonate buffer anion (A(-)). During purely respiratory acidosis, buffer base stays constant because HCO(3)(-) cannot buffer its own progenitor, carbonic acid, so that the rise of HCO(3)(-) equals the fall of A(-). During anaerobic "metabolism," however, lactate's H(+) is buffered by both A(-) and HCO(3)(-), causing buffer base to decrease. We quantified the partitioning of lactate's H(+) between HCO(3)(-) and A(-) buffer in anoxic intestine by compressing intestinal segments of anesthetized swine into a steel pipe and measuring PCO(2) and lactate at 5- to 10-min intervals. Their rises followed first-order kinetics, yielding k = 0. 031 min(-1) and half time = approximately 22 min. PCO(2) vs. lactate relations were linear. Over 3 h, lactate increased by 31 +/- 3 mmol/l tissue fluid (mM) and PCO(2) by approximately 17 mM, meaning that one-half of lactate's H(+) was buffered by tissue HCO(3)(-) and one-half by A(-). The data were consistent with a lumped pK(a) value near 6.1 and total A(-) concentration of approximately 30 mmol/kg. We conclude that the respiratory vs. metabolic distinction could be made in tissue by estimating tissue buffer base from measured pH and PCO(2).
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Affiliation(s)
- O Raza
- Department Research and Development, Veterans Affairs Medical Center, Pittsburgh, Pennsylvania 15240, USA
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Pesquero J, Alfaro V, Palacios L. Acid-base analysis during experimental anemia in rats. Can J Physiol Pharmacol 2000. [DOI: 10.1139/y00-056] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study evaluated the acid-base status of anemic rats by using two approaches of acid-base analysis: one based on the base excess (BE) calculation and the other based on Stewart's physicochemical analysis. Two sets of experimental data, derived from two different methods of inducing anemia, were used: repetitive doses of phenylhydrazine (PHZ) and bleeding (BL). A significant uncompensated respiratory alkalosis was found in both groups of anemic rats. BE increased slightly, whereas strong ion difference ([SID]) and weak acid buffers ([ATOT]) remained unchanged in anemic rats. The reasons for the absence of compensation for hypocapnia and the differences in the behaviour of acid-base variables are discussed. BE increase was considered paradoxical; its calculation was affected by the experimental conditions and BE had little physiological relevance during anemia. The absence of metabolic renal compensation in anemic rats could be due to a lower pH in the kidney due to anemic hypoxia. Finally, the changes in buffer strength related to low Hb and low Pc02 might influence plasma [SID] through counteracted shifts of strong ions between erythrocytes and plasma, finally resulting in unchanged [SID] during anemia.Key words: anemia, phenylhydrazine, bleeding, base excess, strong ion difference, non-carbonic buffers.
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Abstract
Analytic expressions for plasma total titratable base, base excess (DeltaCB), strong-ion difference, change in strong-ion difference (DeltaSID), change in Van Slyke standard bicarbonate (DeltaVSSB), anion gap, and change in anion gap are derived as a function of pH, total buffer ion concentration, and conditional molar equilibrium constants. The behavior of these various parameters under respiratory and metabolic acid-base disturbances for constant and variable buffer ion concentrations is considered. For constant noncarbonate buffer concentrations, DeltaSID = DeltaCB = DeltaVSSB, whereas these equalities no longer hold under changes in noncarbonate buffer concentration. The equivalence is restored if the reference state is changed to include the new buffer concentrations.
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Affiliation(s)
- E W Wooten
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
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Schlichtig R, Grogono AW, Severinghaus JW. CURRENT STATUS OF ACID-BASE QUANTITATION IN PHYSIOLOGY AND MEDICINE. ACTA ACUST UNITED AC 1998. [DOI: 10.1016/s0889-8537(05)70015-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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