Clinical utility of Stewart's method in diagnosis and management of acid-base disorders

Linking preoperative and early intensive care unit data for prolonged intubation prediction

Objectives

Prolonged intubation (PI) is a frequently encountered severe complication among patients following cardiac surgery (CS). Solely concentrating on preoperative data, devoid of sufficient consideration for the ongoing impact of surgical, anesthetic, and cardiopulmonary bypass procedures on subsequent respiratory system function, could potentially compromise the predictive accuracy of disease prognosis. In response to this challenge, we formulated and externally validated an intelligible prediction model tailored for CS patients, leveraging both preoperative information and early intensive care unit (ICU) data to facilitate early prophylaxis for PI.

Methods

We conducted a retrospective cohort study, analyzing adult patients who underwent CS and utilizing data from two publicly available ICU databases, namely, the Medical Information Mart for Intensive Care and the eICU Collaborative Research Database. PI was defined as necessitating intubation for over 24 h. The predictive model was constructed using multivariable logistic regression. External validation of the model's predictive performance was conducted, and the findings were elucidated through visualization techniques.

Results

The incidence rates of PI in the training, testing, and external validation cohorts were 11.8%, 12.1%, and 17.5%, respectively. We identified 11 predictive factors associated with PI following CS: plateau pressure [odds ratio (OR), 1.133; 95% confidence interval (CI), 1.111-1.157], lactate level (OR, 1.131; 95% CI, 1.067-1.2), Charlson Comorbidity Index (OR, 1.166; 95% CI, 1.115-1.219), Sequential Organ Failure Assessment score (OR, 1.096; 95% CI, 1.061-1.132), central venous pressure (OR, 1.052; 95% CI, 1.033-1.073), anion gap (OR, 1.075; 95% CI, 1.043-1.107), positive end-expiratory pressure (OR, 1.087; 95% CI, 1.047-1.129), vasopressor usage (OR, 1.521; 95% CI, 1.23-1.879), Visual Analog Scale score (OR, 0.928; 95% CI, 0.893-0.964), pH value (OR, 0.757; 95% CI, 0.629-0.913), and blood urea nitrogen level (OR, 1.011; 95% CI, 1.003-1.02). The model exhibited an area under the receiver operating characteristic curve (AUROC) of 0.853 (95% CI, 0.840-0.865) in the training cohort, 0.867 (95% CI, 0.853-0.882) in the testing cohort, and 0.704 (95% CI, 0.679-0.727) in the external validation cohort.

Conclusions

Through multicenter internal and external validation, our model, which integrates early ICU data and preoperative information, exhibited outstanding discriminative capability. This integration allows for the accurate assessment of PI risk in the initial phases following CS, facilitating timely interventions to mitigate adverse outcomes.

Clinical Approach to Assessing Acid-Base Status: Physiological vs Stewart

Evaluation of acid-base status depends on accurate measurement of acid-base variables and their appropriate assessment. Currently, 3 approaches are utilized for assessing acid-base variables. The physiological or traditional approach, pioneered by Henderson and Van Slyke in the early 1900s, considers acids as H⁺ donors and bases as H⁺ acceptors. The acid-base status is conceived as resulting from the interaction of net H⁺ balance with body buffers and relies on the H₂CO₃/HCO₃^- buffer pair for its assessment. A second approach, developed by Astrup and Siggaard-Andersen in the late 1950s, is known as the base excess approach. Base excess was introduced as a measure of the metabolic component replacing plasma [HCO₃^-]. In the late 1970s, Stewart proposed a third approach that bears his name and is also referred to as the physicochemical approach. It postulates that the [H⁺] of body fluids reflects changes in the dissociation of water induced by the interplay of 3 independent variables-strong ion difference, total concentration of weak acids, and PCO₂. Here we focus on the physiological approach and Stewart's approach examining their conceptual framework, practical application, as well as attributes and drawbacks. We conclude with our view about the optimal approach to assessing acid-base status.

Association between delta anion gap and hospital mortality for patients in cardiothoracic surgery recovery unit: a retrospective cohort study

Backgrounds

High level of anion gap (AG) was associated with organic acidosis. This study aimed to explore the relationship between delta AG (ΔAG = AG_max − AG_min) during first 3 days after intensive care unit (ICU) admission and hospital mortality for patients admitted in the cardiothoracic surgery recovery unit (CSRU).

Methods

In this retrospective cohort study, we identified patients from the open access database called Multiparameter Intelligent Monitoring in Intensive Care III (MIMIC III). A logistic regression model was established to predict hospital mortality by adjusting confounding factors using a stepwise backward elimination method. We conducted receiver operating characteristic (ROC) curves to compare the diagnostic performance of acid–base variables. Cox regression model and Kaplan Meier curve were applied to predict patients’ 90-day overall survival (OS).

Results

A total of 2,860 patients were identified. ΔAG was an independent predictive factor of hospital mortality (OR = 1.24 per 1 mEq/L increase, 95% CI: 1.11–1.39, p < 0.001). The area under curve (AUC) values of ΔAG suggested a good diagnostic accuracy (AUC = 0.769). We established the following formula to estimate patients’ hospital mortality: Logit(P) = − 15.69 + 0.21ΔAG + 0.13age-0.21BE + 2.69AKF. After calculating Youden index, patients with ΔAG ≥ 7 was considered at high risk (OR = 4.23, 95% CI: 1.22–14.63, p = 0.023). Kaplan Meier curve demonstrated that patients with ΔAG ≥ 7 had a poorer 90-day OS (Adjusted HR = 3.20, 95% CI: 1.81–5.65, p < 0.001).

Conclusion

ΔAG is a prognostic factor of hospital mortality and 90-day OS. More prospective studies are needed to verify and update our findings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12893-022-01625-9.

Acid-Base Disorders in COVID-19 Patients with Acute Respiratory Distress Syndrome

Our aim was to investigate the distribution of acid-base disorders in patients with COVID-19 ARDS using both the Henderson–Hasselbalch and Stewart’s approach and to explore if hypoxemia can influence acid-base disorders. COVID-19 ARDS patients, within the first 48 h of the need for a non-invasive respiratory support, were retrospectively enrolled. Respiratory support was provided by helmet continuous positive airway pressure (CPAP) or by non-invasive ventilation. One hundred and four patients were enrolled, 84% treated with CPAP and 16% with non-invasive ventilation. Using the Henderson–Hasselbalch approach, 40% and 32% of patients presented respiratory and metabolic alkalosis, respectively; 13% did not present acid-base disorders. Using Stewart’s approach, 43% and 33% had a respiratory and metabolic alkalosis, respectively; 12% of patients had a mixed disorder characterized by normal pH with a lower SID. The severe hypoxemic and moderate hypoxemic group presented similar frequencies of respiratory and metabolic alkalosis. The most frequent acid-base disorders were respiratory and metabolic alkalosis using both the Henderson–Hasselbalch and Stewart’s approach. Stewart’s approach detected mixed disorders with a normal pH probably generated by the combined effect of strong ions and weak acids. The impairment of oxygenation did not affect acid-base disorders.

Acid-base balance and cerebrovascular regulation

The regulation and defence of intracellular pH is essential for homeostasis. Indeed, alterations in cerebrovascular acid-base balance directly affect cerebral blood flow (CBF) which has implications for human health and disease. For example, changes in CBF regulation during acid-base disturbances are evident in conditions such as chronic obstructive pulmonary disease and diabetic ketoacidosis. The classic experimental studies from the past 75+ years are utilized to describe the integrative relationships between CBF, carbon dioxide tension (PCO₂ ), bicarbonate (HCO₃ ^- ) and pH. These factors interact to influence (1) the time course of acid-base compensatory changes and the respective cerebrovascular responses (due to rapid exchange kinetics between arterial blood, extracellular fluid and intracellular brain tissue). We propose that alterations in arterial [HCO₃ ^- ] during acute respiratory acidosis/alkalosis contribute to cerebrovascular acid-base regulation; and (2) the regulation of CBF by direct changes in arterial vs. extravascular/interstitial PCO₂ and pH - the latter recognized as the proximal compartment which alters vascular smooth muscle cell regulation of CBF. Taken together, these results substantiate two key ideas: first, that the regulation of CBF is affected by the severity of metabolic/respiratory disturbances, including the extent of partial/full acid-base compensation; and second, that the regulation of CBF is independent of arterial pH and that diffusion of CO₂ across the blood-brain barrier is integral to altering perivascular extracellular pH. Overall, by realizing the integrative relationships between CBF, PCO₂ , HCO₃ ^- and pH, experimental studies may provide insights to improve CBF regulation in clinical practice with treatment of systemic acid-base disorders.

Impact of Acid-Base Status on Mortality in Patients with Acute Pesticide Poisoning

We investigated clinical impacts of various acid-base approaches (physiologic, base excess (BE)-based, and physicochemical) on mortality in patients with acute pesticide intoxication and mutual intercorrelated effects using principal component analysis (PCA). This retrospective study included patients admitted from January 2015 to December 2019 because of pesticide intoxication. We compared parameters assessing the acid-base status between two groups, survivors and non-survivors. Associations between parameters and 30-days mortality were investigated. A total of 797 patients were analyzed. In non-survivors, pH, bicarbonate concentration (HCO₃⁻), total concentration of carbon dioxide (tCO₂), BE, and effective strong ion difference (SIDe) were lower and apparent strong ion difference (SIDa), strong ion gap (SIG), total concentration of weak acids, and corrected anion gap (corAG) were higher than in survivors. In the multivariable logistic analysis, BE, corAG, SIDa, and SIDe were associated with mortality. PCA identified four principal components related to mortality. SIDe, HCO₃⁻, tCO₂, BE, SIG, and corAG were loaded to principal component 1 (PC1), referred as total buffer bases to receive and handle generated acids. PC1 was an important factor in predicting mortality irrespective of the pesticide category. PC3, loaded mainly with pCO₂, suggested respiratory components of the acid-base system. PC3 was associated with 30-days mortality, especially in organophosphate or carbamate poisoning. Our study showed that acid-base abnormalities were associated with mortality in patients with acute pesticide poisoning. We reduced these variables into four PCs, resembling the physicochemical approach, revealed that PCs representing total buffer bases and respiratory components played an important role in acute pesticide poisoning.

Acid-base effects of continuous infusion furosemide in clinically stable surgical ICU patients: an analysis based on the Stewart model

OBJECTIVES

We sought to test the strength of correlation between predicted and observed systemic acid-base status based on the Stewart model equations during continuous infusion (CI) furosemide therapy.

DESIGN, SETTING AND PARTICIPANTS

This was a prospective, single-center, observational study conducted in the Surgical ICU of a large academic medical center. Ten critically ill patients who received CI furosemide were included.

MAIN OUTCOMES AND MEASURES

The primary purpose was to characterize the relationship between changes in serum electrolyte and acid-base status and the excretion of electrolytes in the urine during infusion of CI furosemide in critically ill patients. As a secondary endpoint, we sought to evaluate the predictive application of the Stewart model. Over 72-h, intake and output volumes, electrolyte content of fluids administered, plasma and urine electrolytes, urine pH, and venous blood gases were collected. Predicted and observed changes in acid-based status were compared for each day of diuretic therapy using Spearman's correlation coefficient.

RESULTS

The mean (SD) strong ion difference (SID) increased from 45.2 (3.2) at baseline to 49.6 (4.0) after 72 h of continuous infusion furosemide. At Day 1, the mean SID (observed) (SD) was 47.5 (3.5) and the predicted SID was 49.5 (5.8). Day 1 observed plasma SID was positively correlated with the predicted SID (r_s = 0.80, p = 0.01). By Days 2 and 3, the correlations of observed and predicted SID were no longer statistically significant.

CONCLUSIONS AND RELEVANCE

Using the Stewart model, increases in SID as an indicator of metabolic alkalosis due to the chloruretic effects of furosemide were observed. Predicted and observed SID correlated well over the first 24 h of treatment.

Connecting two worlds: positive correlation between physicochemical approach with blood gases and pH in pediatric ICU setting

Objective

Physicochemical approach such as strong ion difference provides a novel concept in understanding and managing acid–base disturbance in patients. However, its application in pediatrics is limited. This study aimed to evaluate a correlation between the physicochemical approach and blood gas pH for acid–base determination in critically ill pediatric patients.

Results

A total of 130 pediatric patients were included, corresponding to 1338 paired measures for analyses. Of these, the metabolic subgroup (743 paired measures) was defined. Among physicochemical parameters, the effective strong ion difference showed the best correlation with the blood gas pH in the whole cohort (R = 0.398; p < 0.001) and the metabolic subgroup (R = 0.685; p < 0.001). Other physicochemical parameters (i.e., the simplified and the apparent strong ion difference, the strong ion gap, and the sodium chloride gap) and the traditional measures (standard base excess, lactate, chloride and bicarbonate) also showed varying degrees of correlation. This study revealed the positive correlation between physicochemical parameters and the blood gas pH, serving as a connecting dot for further investigations using physicochemical approach to evaluate acid–base disturbance in pediatric population.

Traditional approach versus Stewart approach for acid-base disorders: Inconsistent evidence

Purpose

The traditional approach and the Stewart approach have been developed for evaluating acid-base phenomena. While some experts have suggested that the two approaches are essentially identical, clinical researches have still been conducted on the superiority of one approach over the other one. In this review, we summarize the concepts of each approach and investigate the reasons of the discrepancy, based on current evidence from the literature search.

Methods

In the literature search, we completed a database search and reviewed articles comparing the Stewart approach with the traditional, bicarbonate-centered approach to November 2016.

Results

Our literature review included 17 relevant articles, 5 of which compared their diagnostic abilities, 9 articles compared their prognostic performances, and 3 articles compared both diagnostic abilities and prognostic performances. These articles show a discrepancy over the abilities to detect acid-base disturbances and to predict patients' outcomes. There are many limitations that could yield this discrepancy, including differences in calculation of the variables, technological differences or errors in measuring variables, incongruences of reference value, normal range of the variables, differences in studied populations, and confounders of prognostic strength such as lactate.

Conclusion

In conclusion, despite the proposed equivalence between the traditional approach and the Stewart approach, our literature search shows inconsistent results on the comparison between the two approaches for diagnostic and prognostic performance. We found crucial limitations in those studies, which could lead to the reasons of the discrepancy.

Modern and traditional approaches combined into an effective gray-box mathematical model of full-blood acid-base

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.

Is There a Role for Balanced Solutions in Septic Patients?

The use of fluid bolus infusion is the cornerstone for hemodynamic resuscitation of critically ill patients. Recently, the clinical use of colloids has lost strength with the publication of several trials suggesting no benefit, and possible harm of its use.On the other hand, the so-called balanced solutions, with low chloride concentrations, have emerged as an alternative with potential physiological benefits over traditional saline solution. Normal saline carries a high amount of chloride which has been associated with an increased incidence of metabolic acidosis, renal vasoconstriction, and reduced urine output. Recent observational studies associated the use of saline with acute kidney injury, which was not observed in a single prospective randomized controlled trial.The present review summarizes available literature regarding the potential clinical and laboratorial benefits of balanced solutions in septic patients.

Determination of tissue hypoxia by physicochemical approach in premature anemia

BACKGROUND

Anemia is a common problem in premature infants and its most rapid and effective therapy is erythrocyte transfusion. However, owing to inherent risks of transfusion in this population, transfusions should be administered only when adequate oxygen delivery to tissues is impaired. The aim of this study was to determine tissue acid levels using Stewart method in an attempt to evaluate the tissue oxygenation level and thereby the accuracy of transfusion timing.

METHODS

This study included 47 infants delivered at gestational age below 34 weeks who required erythrocyte transfusion for premature anemia. Strong ion gap (SIG), unmeasurable anions (UMA), tissue acid levels (TA), and Cl/Na ratios were calculated before and after transfusion.

RESULTS

The mean birth weight and gestational age of the study population were 1210 ± 365 g and 29.2 ± 2.7 weeks, respectively. Tissue acid levels were increased (TA ≥ 4) and tissue hypoxia developed in 10 (16.6%) of 60 erythrocyte transfusions administered according to the restrictive transfusion approach. The patients were divided into two groups according to tissue acid levels as low (<4) and high (≥4) tissue acid groups. The group with tissue hypoxia (TA ≥ 4) had significantly higher UMA levels but a significantly lower Cl/Na ratio; and UMA levels decreased and Cl/Na ratio increased after transfusion in this group. Tissue hypoxia secondary to anemia was shown to be improved by erythrocyte transfusion.

CONCLUSION

The results of the present study suggest that the determination of the level of tissue hypoxia by the Stewart approach may be an alternative to restrictive transfusion guidelines for timing of transfusion in premature anemia. It also showed that a low Cl/Na ratio can be used as a simple marker of tissue hypoxia.

Acid-base disturbances in nephrotic syndrome: analysis using the CO2/HCO3 method (traditional Boston model) and the physicochemical method (Stewart model)

Background

The Stewart model for analyzing acid–base disturbances emphasizes serum albumin levels, which are ignored in the traditional Boston model. We compared data derived using the Stewart model to those using the Boston model in patients with nephrotic syndrome.

Methods

Twenty-nine patients with nephrotic syndrome and six patients without urinary protein or acid–base disturbances provided blood and urine samples for analysis that included routine biochemical and arterial blood gas tests, plasma renin activity, and aldosterone. The total concentration of non-volatile weak acids (A_TOT), apparent strong ion difference (SIDa), effective strong ion difference (SIDe), and strong ion gap (SIG) were calculated according to the formulas of Agrafiotis in the Stewart model.

Results

According to the Boston model, 25 of 29 patients (90%) had alkalemia. Eighteen patients had respiratory alkalosis, 11 had metabolic alkalosis, and 4 had both conditions. Only three patients had hyperreninemic hyperaldosteronism. The Stewart model demonstrated respiratory alkalosis based on decreased PaCO₂, metabolic alkalosis based on decreased A_TOT, and metabolic acidosis based on decreased SIDa. We could diagnose metabolic alkalosis or acidosis with a normal anion gap after comparing delta A_TOT [(14.09 − measured A_TOT) or (11.77 − 2.64 × Alb (g/dL))] and delta SIDa [(42.7 − measured SIDa) or (42.7 − (Na + K − Cl)]). We could also identify metabolic acidosis with an increased anion gap using SIG > 7.0 (SIG = 0.9463 × corrected anion gap—8.1956).

Conclusions

Patients with nephrotic syndrome had primary respiratory alkalosis, decreased A_TOT due to hypoalbuminemia (power to metabolic alkalosis), and decreased levels of SIDa (power to metabolic acidosis). We could detect metabolic acidosis with an increased anion gap by calculating SIG. The Stewart model in combination with the Boston model facilitates the analysis of complex acid–base disturbances in nephrotic syndrome.

Assessing Acid-Base Status: Physiologic Versus Physicochemical Approach

The physiologic approach has long been used in assessing acid-base status. This approach considers acids as hydrogen ion donors and bases as hydrogen ion acceptors and the acid-base status of the organism as reflecting the interaction of net hydrogen ion balance with body buffers. In the physiologic approach, the carbonic acid/bicarbonate buffer pair is used for assessing acid-base status and blood pH is determined by carbonic acid (ie, Paco₂) and serum bicarbonate levels. More recently, the physicochemical approach was introduced, which has gained popularity, particularly among intensivists and anesthesiologists. This approach posits that the acid-base status of body fluids is determined by changes in the dissociation of water that are driven by the interplay of 3 independent variables: the sum of strong (fully dissociated) cation concentrations minus the sum of strong anion concentrations (strong ion difference); the total concentration of weak acids; and Paco₂. These 3 independent variables mechanistically determine both hydrogen ion concentration and bicarbonate concentration of body fluids, which are considered as dependent variables. Our experience indicates that the average practitioner is familiar with only one of these approaches and knows very little, if any, about the other approach. In the present Acid-Base and Electrolyte Teaching Case, we attempt to bridge this knowledge gap by contrasting the physiologic and physicochemical approaches to assessing acid-base status. We first outline the essential features, advantages, and limitations of each of the 2 approaches and then apply each approach to the same patient presentation. We conclude with our view about the optimal approach.

Effectiveness of the Stewart Method in the Evaluation of Blood Gas Parameters

Objectives

In 1981, Peter A. Stewart published a paper describing his concept for employing Strong Ion Difference. In this study we compared the HCO₃ levels and Anion Gap (AG) calculated using the classic method and the Stewart method.

Methods

Four hundred nine (409) arterial blood gases of 90 patients were collected retrospectively. Some were obtained from the same patients in different times and conditions. All blood samples were evaluated using the same device (ABL 800 Blood Gas Analyzer). HCO₃ level and AG were calculated using the Stewart method via the website AcidBase.org. HCO₃ levels, AG and strong ion difference (SID) were calculated using the Stewart method, incorporating the parameters of age, serum lactate, glucose, sodium, and pH, etc.

Results

According to classic method, the levels of HCO₃ and AG were 22.4±7.2 mEq/L and 20.1±4.1 mEq/L respectively. According to Stewart method, the levels of HCO₃ and AG were 22.6±7.4 and 19.9±4.5 mEq/L respectively.

Conclusions

There was strong correlation between the classic method and the Stewart method for calculating HCO₃ and AG. The Stewart method may be more effective in the evaluation of complex metabolic acidosis.

Ion-selective electrode and anion gap range: What should the anion gap be?

Background

Using flame photometry technique in the 1970s, the normal value of anion gap (AG) was determined to be 12 ± 4 meq/L. However, with introduction of the autoanalyzers using an ion-selective electrode (ISE), the anion gap value has fallen to lower levels.

Methods

A retrospective study of US veterans from a single medical center was performed to determine the value of the anion gap in subjects with normal renal function and normal serum albumin and in patients with lactic acidosis and end-stage renal disease on dialysis.

Results

In 409 patients with an estimated glomerular filtration rate ≥60 mL/min/1.73 m² body surface area and serum albumin ≥4 g/dL, the mean AG was 7.2 ± 2 (range 3–11) meq/L. In 299 patients with lactic acidosis (lactate level ≥4 meq/L) and 68 patients with endstage renal disease on dialysis, the mean AG was 12.5 meq/L and 12.4 meq/L, respectively. A value <2 meq/L should be considered a low anion gap and a possible clue to drug intoxication and paraproteinemic disorders.

Conclusion

With the advent of ISE for measurement of analytes, the value of the anion gap has fallen. Physicians need to be aware of the normal AG value in their respective institutions, and laboratories need to have an established value for AG based on the type of instrument they are using.

The difference between critical care initiation anion gap and prehospital admission anion gap is predictive of mortality in critical illness

OBJECTIVE

We hypothesized that the delta anion gap defined as difference between critical care initiation standard anion gap and prehospital admission standard anion gap is associated with all cause mortality in the critically ill.

DESIGN

Observational cohort study.

SETTING

Two hundred nine medical and surgical intensive care beds in two hospitals in Boston, MA.

PATIENTS

Eighteen thousand nine hundred eighty-five patients, age ≥18 yrs, who received critical care between 1997 and 2007.

MEASUREMENTS

The exposure of interest was delta anion gap and categorized a priori as <0, 0-5, 5-10, and >10 mEq/L. Logistic regression examined death by days 30, 90, and 365 postcritical care initiation and in-hospital mortality. Adjusted odds ratios were estimated by multivariable logistic regression models. The discrimination of delta anion gap for 30-day mortality was evaluated using receiver operator characteristic curves performed for a subset of patients with all laboratory data required to analyze the data via physical chemical principles (n = 664).

INTERVENTIONS

None.

RESULTS

Delta anion gap was a particularly strong predictor of 30-day mortality with a significant risk gradient across delta anion gap quartiles following multivariable adjustment: delta anion gap <0 mEq/L odds ratio 0.75 (95% confidence interval 0.67-0.81; p < 0.0001); delta anion gap 5-10 mEq/L odds ratio 1.56 (95% confidence interval 1.35-1.81; p < 0.0001); delta anion gap >10 mEq/L odds ratio 2.18 (95% confidence interval 1.76-2.71; p < 0.0001); and all relative to patients with delta anion gap 0-5 mEq/L. Similar significant robust associations post multivariable adjustments are seen with death by days 90 and 365 as well as in-hospital mortality. Correcting for albumin or limiting the cohort to patients with standard anion gap at critical care initiation of 10-18 mEq/L did not materially change the delta anion gap-mortality association. Delta anion gap has similarly moderate discriminative ability for 30-day mortality in comparison to standard base excess and strong ion gap.

CONCLUSION

An increase in standard anion gap at critical care initiation relative to prehospital admission standard anion gap is a predictor of the risk of all cause patient mortality in the critically ill.

Desenvolvimento de software para interpretação de dados gasométricos aplicável em unidades de terapia intensiva

O objetivo deste estudo foi desenvolver um software para interpretação de dados gasométricos aplicável em UTIs. Trata-se de estudo de caráter experimental, sendo selecionada uma base teórica em Java com a IDE NetBeans 6.8 por meio de parceria com profissionais capacitados em Sistemas de Informação. O desenvolvimento do programa foi baseado na criação de um algoritmo, uma sequência de instruções bem definidas e não ambíguas a serem executadas mecanicamente com a finalidade de fornecer um diagnóstico desejado. Foi criado um software aplicável em UTIs denominado InterGas, que é um programa de fácil instalação, possui interface de fácil compreensão e utilização, além de processar os dados rapidamente e de forma precisa, oferecendo como resultado final o diagnóstico para o distúrbio do equilíbrio ácido-básico. O desconhecimento de outra ferramenta que reúna todos os componentes do InterGas o torna um software pioneiro que facilita a tomada de decisão à medida que caracteriza a ocorrência de distúrbios mistos utilizando fórmulas de compensação. Com isso, futuros estudos deverão ser feitos com o objetivo de avaliar aspectos relacionados à implementação e eficácia do software desenvolvido.

Acid-base disorders in patients with chronic obstructive pulmonary disease: a pathophysiological review

The authors describe the pathophysiological mechanisms leading to development of acidosis in patients with chronic obstructive pulmonary disease and its deleterious effects on outcome and mortality rate. Renal compensatory adjustments consequent to acidosis are also described in detail with emphasis on differences between acute and chronic respiratory acidosis. Mixed acid-base disturbances due to comorbidity and side effects of some drugs in these patients are also examined, and practical considerations for a correct diagnosis are provided.

Extreme metabolic alkalosis in intensive care

Metabolic alkalosis is a commonly seen imbalance in the intensive care unit (ICU). Extreme metabolic alkalemia, however, is less common. A pH greater than 7.65 may carry a high risk of mortality (up to 80%). We discuss the entity of life threatening metabolic alkalemia by means of two illustrative cases - both with a pH greater than 7.65 on presentation. The cause, modalities of managing and complications of this condition is discussed from the point of view of both the traditional method of Henderson and Hasselbalch and the mathematical model based on physiochemical model described by Stewart. Special mention to the pitfalls in managing patients of metabolic alkalosis with concomitant renal compromise is made.