Strong ion gap and anion gap corrected for albumin and lactate in patients with sepsis in the intensive care unit.

INTRODUCTION: Metabolic acidosis is very common amongst critically ill sepsis patients partly due to the presence of unmeasured ions in serum. These ions can be detected by anion gap (AG) or strong ion gap (SIG) concentration values. The purpose of this study is to assess the correlation and potential agreement of the two methods in critically ill patients with sepsis. MATERIALS AND METHODS: The present is a retrospective study including septic patients admitted to the Intensive Care Unit from December 2014 to July 2016. The [SIG] and the [AG] corrected for albumin and lactate ([AGcl]) were calculated on admission and on sepsis remission or deterioration. The correlation of the two parameters was assessed in all patient groups using the Pearson correlation coefficient and linear regression analysis and the agreement with Bland-Altman plots. ROC survival curves were also generated for the patients in relation to the values of [AGcl], [SIG] and inorganic [SIG] ([SIGi]) on admission. RESULTS: There was a strong correlation linking [AGcl] and [SIG] values (r>0.9, P<0.05) in all patient groups. The results from all three linear regression equations were statistically significant as the models predicted the [AGcl] value from the [SIG] value with high accuracy. The mean difference of the two methods (i.e. [AGcl] - [SIG] in every patient separately) in septic patients on admission was 11.75 mEq/l with 95% limits of agreement [9.7-13.8]; in patients with sepsis deterioration, it was 11.8 mEq/l with 95% limits of agreement [9.8-13.7] and in patients with sepsis remission, it was 11.5 mEq/l with 95% limits of agreement [10.4-12.7]. ROC survival curves demonstrated a small area under the curve (AUC): [SIG] AUC: 0.479, 95% CI [0.351, 0.606], [SIGi] AUC: 0.581, 95% CI [0.457, 0.705], [AGcl] AUC: 0.529, 95% CI [0.401, 0.656]. CONCLUSION: [AGcl] and [SIG] demonstrate excellent correlation in septic patients, with a mean difference of about 12 mEq/l. Both parameters failed to demonstrate any predictive ability regarding patient mortality.

Elevated strong ion gap: A predictor of the initiation of continuous renal replacement therapy in acute kidney injury.

BACKGROUND: There is no optimal timing for continuous renal replacement therapy (CRRT) in acute kidney injury (AKI). AKI is a reason for the increased unmeasured anions, which refers to the increased organic acids in the blood, and they can be detected by calculating strong ion gap (SIG). SIG level at the moment of the AKI diagnosis may be a predictor for the initiation of CRRT. METHODS: Patients who were diagnosed with AKI in the first week of the intensive care unit (ICU) period were included in this prospective observational study. At the moment of the AKI diagnosis, blood gas samples were recorded, and SIG was calculated. RESULTS: The median level of SIG at the moment of the AKI diagnosis of CRRT (+) patients was significantly higher than CRRT (-) patients (7.4 and 3.2 mmol L-1, respectively). In the multivariate Cox regression analysis, the likelihood of the initiation of CRRT was increased 1.16-fold (1.01-1.33) and 4.0-fold (1.9-8.7) by only 1 mmol L-1 increases in SIG and SIG ≥6 mmol L-1 at the moment of AKI diagnosis, respectively (p = 0.035 and p < 0.001). CONCLUSIONS: Increased SIG at the moment of the AKI diagnosis in patients with AKI may be a predictive marker to initiate CRRT.

Prognosis assessment of strong ion gap in adult patients with cardiac arrest / 中华急诊医学杂志

Objective:To investigate the correlation between strong ion gap (SIG) and prognosis of adult hospitalized patients who experienced cardiac arrest (CA).Methods:A retrospective cohort study was conducted on adult CA patients (≥18 years old) who were admitted to the intensive care unit (ICU) for the first time from the Medical Information Mart for Intensive Care Ⅲ (MIMIC-Ⅲ) database from 2001 to 2012. The patients were divided into 3 groups based on the tertiles of serum SIG value. The clinical baseline characteristics and related data of CA patients were compared. Kaplan-Meier method was used to draw the 28- and 90-day cumulative survival curves of CA patients. Meanwhile, the log-rank test was used to compare the differences in the survival curves among different groups, and Cox proportional hazard regression model was established to analyze whether SIG was an independent predictor of all-cause mortality in CA patients.Results:Six hundred and six adult CA patients were eligible for final analysis. The patients were divided into 3 groups based on the tertiles of serum SIG value [<3.91 mmol/L ( n=202), 3.91~7.32 mmol/L ( n=202) and >7.32 mmol/L ( n=202)]. The mean age was (66.91±15.95) years and 382 patients (63.04%) were male. The all-cause mortality rates of ICU, 28 days and 90 days were 36.47%, 49.17% and 56.93%, respectively. There were significant differences in SOFA score, SIG, anion gap, pH, lactic acid, white blood cells, prothrombin time, creatinine, blood potassium, blood phosphorus, hypertension, coronary heart disease, cardiogenic shock, and ICU, 28-day and 90-day all-cause mortality among the 3 groups (all P<0.05). The Kaplan-Meier survival curves showed that the 28- and 90-day cumulative survival rates of CA patients decreased gradually with the increase of SIG level, and the differences were statistically significant among the 3 groups (all P<0.001). Multivariate Cox proportional hazard models showed that the increase of SIG level (>7.32 mmol/L) was an independent risk factor for 28-day ( HR=1.610, 95% CI: 1.177-2.203, P=0.003) and 90-day all-cause mortality ( HR=1.506, 95% CI: 1.123-2.019, P=0.006) among CA patients, after adjusting for the related confounders. Conclusions:The elevated SIG level (>7.32 mmol/L) is an independent predictor of 28- and 90-day all-cause mortality in CA patients. The calculation of SIG level in these patients is helpful for early identification of patients with poor prognosis.

Stewart analysis unmasks acidifying and alkalizing effects of ionic shifts during acute severe respiratory alkalosis.

PURPOSE: Although both the Henderson-Hasselbalch method and the Stewart approach can be used to analyze acid-base disturbances and metabolic and respiratory compensation mechanisms, the latter may be superior in detecting subtle metabolic changes. MATERIALS AND METHODS: We analyzed acid-base disturbances using both approaches in six healthy male volunteers practicing extreme voluntary hyperventilation. Arterial blood gas parameters were obtained during a breathing exercise consisting of approximately 30 cycles of powerful hyperventilation followed by breath retention for approximately 2 min. RESULTS: Hyperventilation increased pH from 7.39 ± 0.01 at baseline to 7.74 ± 0.06, PaCO2 decreased from 34.1 ± 1.1 to 12.6 ± 0.7 mmHg, PaO2 increased from 116 ± 4.6 to 156 ± 4.3 mmHg. Baseline apparent strong ion difference was 42.3 ± 0.5 mEq/L, which decreased to 37.1 ± 0.7 mEq/L following hyperventilation. The strong ion gap significantly decreased following hyperventilation, with baseline levels of 10.0 ± 0.9 dropping to 6.4 ± 1.1 mEq/L. CONCLUSIONS: Henderson-Hasselbalch analysis indicated a profound and purely respiratory alkalosis with no metabolic compensation following extreme hyperventilation. The Stewart approach revealed metabolic compensation occurring within minutes. These results challenge the long-held axiom that metabolic compensation of acute respiratory acid-base changes is a slow process.

Reducing complexity in acid-base diagnosis - how far should we go?

PURPOSE: To place in context the potential value of isolated plasma strong ion difference (SID) calculations and strong ion gap (SIG) calculations versus suggested cut-down versions such as SIDa adj and the BICgap respectively. METHODS: Stewart's physical chemical approach is seen as a mathematical model of isolated plasma not displacing traditional Copenhagen and Boston approaches. Scanning tools for unmeasured ions based on the Principle of Electrical Neutrality such as the SIG and suggested cut-down versions such as the albumin adjusted anion gap and the BICgap are evaluated for accuracy and clinical usefulness. RESULTS: Plasma SID and abbreviations such as SIDa adj are not independent variables in vivo since they vary with PCO due to Gibbs Donnan ion traffic. They can also exhibit positive and negative bias, and SID values must be partnered with non-volatile weak acid concentrations when evaluating metabolic acid-base status. The BICgap calculation is a cut down version of the SIG fixed for pH 7.4. It includes phosphate but is otherwise similar in form to the albumin corrected anion gap, with similar sensitivity and specificity characteristics. CONCLUSIONS: Clinicians are unlikely to find SID calculations or cut-down versions such as the SIDa adj clinically useful. The albumin corrected anion gap is in current use and easily determined by mental arithmetic from point of care anion gap printouts plus recent plasma albumin measurements. Any slight advantage of the BICgap would be offset by the complexity of its calculation.

Value of strong ion gap for predicting acute heart failure after acute myocardial infarction / 中华急诊医学杂志

Objective To investigate the value of strong ion gap (SIG) for predicting acute heart failure (AHF) after acute myocardial infarction. Methods A total of 189 patients with acute myocardial infarction were enrolled from July 2015 to December 2016 in the First Affiliated Hospital of Soochow University. Based on AHF occurrence, the patients were divided into the AHF group (n=76) and the non-AHF group (n=113). General clinical data and laboratory tests were compared between the two groups. The univariate analysis and multivariate logistic regression analysis were performed to estimate the contribution of clinical risk factors to triggering AHF after acute myocardial infarction. Spearman correlation analysis was performed to estimate the correlation between SIG and Killip classification. Receiver operating characteristic (ROC) curves were plotted to evaluate the predictive value of ALB, anion gap (AG) and SIG in AHF after acute myocardial infarction. Results Age, proportion of history of diabetes, the serum level of C-reactive protein (CRP), AG and SIG of the AHF group were higher than those of the non-AHF group (P<0.05). Meanwhile, the serum level of albumin (ALB) of the AHF group were lower than those of the non-AHF group (P<0.05). Univariate analysis showed AHF after acute myocardial infarction was closely associated with age, history of diabetes, serum ALB, AG and SIG (P<0.05). Multivariate logistic regression analysis showed that history of diabetes (OR=2.034, 95％CI:1.075-4.113, P<0.05) and SIG (OR=2.445, 95％CI: 1.538-4.297, P<0.05) were significantly correlated with AHF after acute myocardial infarction. The ROC analysis revealed SIG (AUC=0.837,95％CI:0.781-0.893) had a large area under curve compared to ALB (AUC=0.671,95％CI: 0.593-0.750) and AG (AUC=0.728,95％CI: 0.654-0.802). The optimal diagnostic intercept value was 5.24 mmol/L, and the sensitivity and specificity were 76.32％ and 78.36％, respectively. Conclusions SIG could be used as an independent predictor for AHF secondary to acute myocardial infarction, and was significantly correlated with severity of AHF.

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.

Metabolic acidosis and the role of unmeasured anions in critical illness and injury.

Acid-base disorders are frequently present in critically ill patients. Metabolic acidosis is associated with increased mortality, but it is unclear whether as a marker of the severity of the disease process or as a direct effector. The understanding of the metabolic component of acid-base derangements has evolved over time, and several theories and models for precise quantification and interpretation have been postulated during the last century. Unmeasured anions are the footprints of dissociated fixed acids and may be responsible for a significant component of metabolic acidosis. Their nature, origin, and prognostic value are incompletely understood. This review provides a historical overview of how the understanding of the metabolic component of acid-base disorders has evolved over time and describes the theoretical models and their corresponding tools applicable to clinical practice, with an emphasis on the role of unmeasured anions in general and several specific settings.

Evaluation of strong ion gap and other indicators on prognosis of severe pneumonia in children / 中国小儿急救医学

Objective To investigate the value of strong ion gap (SIG),anion gap (AG),and the anionic gap corrected by albumin (ACAG) and lactate in evaluating the prognosis of severe pneumonia in children. Methods Pediatric patients with severe pneumonia hospitalized in the Affiliated Hospital of North Sichuan Medical College from June 2014 to June 2017 were selected as study subjects. A total of 20 death pa-tients (death group) and 59 survivors (survival group) were analyzed respectively according to their progno-sis. The data of Na + ,K + ,Cl - ,HCO -3 ,Mg2 + ,Ca2 + ,pH,PaCO2 ,P,albumin and lactate were obtained from blood gas analysis and blood biochemistry. Based on these data,ACAG was calculated by the Henderson-hasselbalach formula and SIG was calculated by the Stewart-Figge formula. Results There were significant differences in ACAG,SIG,and lactate levels between death group and survival group(P < 0. 05). The area under the ROC curve of ACAG was 0. 756,and the area under the ROC curve of SIG was 0. 936,which were larger than the area under the diagnostic reference line (P < 0. 05),the results were statistically significant. The sensitivity and specificity of ACAG was 79. 7％ and 70. 0％ respectively,and the cut off was 12. 7. The sensitivity and specificity of SIG was 81. 4％ and 95. 5％ respectively,and the cut off was 2. 7. Conclusion SIG,ACAG and lactate have the guiding value in assessing the prognosis of children with severe pneumonia. Meanwhile,SIG has a greater guiding significance for the assessment of the prognosis of children with severe pneumonia.

Value of strong ion gap for predicting the severity of acute pancreatitis / 中华急诊医学杂志

Objective To investigate the value of strong ion gap (SIG) in predicting the severity of acute pancreatitis (AP) based on the revised Atlanta classification. Methods A total of 133 patients with AP admitted from January, 2015 to December, 2016 were enrolled. Of them, there were 55 with mild AP (MAP), 52 with moderately severe AP (MSAP) and 26 with severe AP (SAP). All patients with AP conformed to the diagnostic criteria of Guidelines or Diagnosis and Treatment of Acute Pancreatitis set in 2014 in China. Patients with other underlying diseases that might influence the clinical outcome were excluded, including those with diabetic ketoacidosis, chronic renal failure and other disorders. The changes in blood SIG levels in each group were observed. The correlations between SIG and acute physiology, chronic health evaluation (APACHE) Ⅱ score, Ranson score and length of hospital stay were analyzed. The receiver operating characteristic curves (ROC) were plotted to determine the efficiency of SIG, Scr, APACHE Ⅱ score, and Ranson score for predicting the severity of acute pancreatitis. Results The level of SIG in the SAP group was the highest, followed by the MSAP group and the lowest in the MAP group.There were significant differences in pairwise comparisons (P<0.01). The correlations between SIG and APACHE Ⅱ score (r=0.567, P<0.01), Ranson score (r=0.502, P<0.01), and length of hospital stay were positive (r=0.589, P<0.01). There was no statistical difference in the area under curve (AUC) between SIG and APACHE Ⅱ score (0.874±0.029 vs.0.895±0.025, P>0.05) and as well as Ranson score (0.874±0.029 vs. 0.890±0.027, P>0.05) for predicting moderately-severe acute pancreatitis, but SIG was superior to Scr (0.874±0.029 vs. 0.735±0.043, P<0.01). There was a significant difference in AUC between SIG and Scr (0.910±0.030 vs. 0.755±0.054, P<0.01), but no statistical differences between SIG and APACHE Ⅱ score (0.910±0.030 vs. 0.867±0.034, P>0.05) and Ranson score (0.910±0.030 vs. 0.871±0.032, P>0.05) for predicting severe acute pancreatitis. Conclusion SIG has important clinical significance for predicting the severity of acute pancreatitis.

Chloride:Sodium Ratio May Accurately Predict Corrected Chloride Disorders and the Presence of Unmeasured Anions in Dogs and Cats.

Disorders of chloride and mixed acid-base disturbances are common in veterinary emergency medicine. Rapid identification of these alterations and the presence of unmeasured anions aid prompt patient assessment and management. This study aimed to determine in dogs and cats if site-specific reference values for [Cl-]:[Na+] ratio and [Na+] - [Cl-] difference accurately identify corrected chloride abnormalities and to evaluate the predictive ability of the [Cl-]:[Na+] ratio for the identification of unmeasured anions. A database containing 33,117 canine, and 7,604 feline blood gas and electrolyte profiles was generated. Institution reference intervals were used to calculate site-specific reference values for the [Cl-]:[Na+] ratio and the [Na+] - [Cl-] difference. Contingency tables were used to assess the ability of these values to correctly identify corrected chloride disorders. Unmeasured anions were estimated by calculating strong ion gap (SIG). Continuous variables were compared using the Mann-Whitney U test. Correlations between continuous variables were assessed using Spearman's rho (rs). In dogs, site-specific reference values for the [Cl-]:[Na+] ratio correctly identified 94.6% of profiles as hyper-, normo-, or hypochloremic. For dogs with normal sodium concentrations, site-specific reference values for the [Na+] - [Cl-] difference correctly identified 97.0% of profiles. In dogs with metabolic acidosis (base deficit > 4.0), [Cl-]:[Na+] ratio and SIG were moderately but significantly negatively correlated (rs -0.592, P < 0.0001). SIG was significantly greater in dogs with metabolic acidosis and hypochloremia compared to those without hypochloremia (P < 0.0001). In cats, site-specific reference values for the [Cl-]:[Na+] ratio correctly identified 93.3% of profiles as hyper-, normo-, or hypochloremic, while site-specific reference values for [Na+] - [Cl-] difference correctly identified 95.1% of profiles. In cats with metabolic acidosis [Cl-]:[Na+] ratio and SIG were moderately significantly negatively correlated (rs -0.730, P < 0.0001). SIG was significantly greater in cats with metabolic acidosis and hypochloremia compared to those without hypochloremia (P < 0.0001). Site-specific values for [Cl-]:[Na+] ratio and [Na+] - [Cl-] difference accurately identify corrected chloride disorders in both dogs and cats and may aid identification of the presence of unmeasured anions.

Determination of reference intervals of acid-base parameters in clinically healthy dogs.

OBJECTIVE: To establish reference intervals for traditionally- and Stewart's approach-determined acid-base parameters in a population of clinically healthy dogs. DESIGN: Prospective study (June 2011-September 2012). SETTING: Veterinary teaching hospital. ANIMALS: Two hundred twenty-four client-owned, clinically healthy dogs. INTERVENTIONS: Blood was collected from the jugular vein and the dorsal pedal artery. MEASUREMENTS AND MAIN RESULTS: In the whole blood samples, pH, PCO2 , and PO2 were measured and HCO3- , standard and total bicarbonate, base excess, oxygen content, and alveolar-arterial oxygen differences were calculated. Plasma sodium, potassium, chloride, calcium, albumin, and lactate concentrations were measured and the following parameters were calculated separately for venous and arterial samples: anion gap, anion gap corrected for albumin and phosphate, sodium chloride difference and ratio, chloride gap, strong ion difference, strong ion gap, and unmeasured anions. CONCLUSION: Reference intervals for traditionally- and Stewart's approach-determined acid-base parameters were established for venous and arterial blood in dogs.

The Significance of Strong Ion Gap for Predicting Return of Spontaneous Circulation in Patients with Cardiopulmonary Arrest.

Useful parameters that can predict return of spontaneous circulation (ROSC) in patients with cardiopulmonary arrest (CPA) have not been established. We previously reported the usefulness of anion gap (AG) and albumin-corrected anion gap (ACAG) calculated from a blood sample obtained on arrival at the hospital for the prediction of ROSC. Otherwise, it has been reported that strong ion gap (SIG), which shows the difference between the levels of fully dissociated cations and anions in the serum, is useful to predict the prognosis of critically ill patients. This was a prospective and observational clinical study. Patients with CPA transferred to the emergency department of our hospital between January 2013 and December 2014 were evaluated. Patients were divided into two groups: patients who obtained ROSC [ROSC(+) group] and those who did not [ROSC(-) group]. We compared AG, ACAG and SIG between the two groups. A total of 170 patients were enrolled. Fifty patients were included in the ROSC(+) group, and the remaining 120 in the ROSC(-) group. Both AG and ACAG were significantly better in the ROSC(+) group; however, there was no significant difference in SIG between the two groups. The area under the receiver operating characteristic curves (AUC) for ROSC of both AG and ACAG were almost the same (0.72 and 0.708, respectively); the AUC of SIG (0.57) was inferior to those of AG and ACAG. Our results suggest that AG and ACAG can better predict ROSC following cardiopulmonary resuscitation (CPR) compared with SIG.

Brecha de iones fuertes y su cinética de aclaramiento como marcador de mortalidad en pacientes con choque séptico / Strong ion gap and its clearance kinetics as a mortality marker in septic shock patients / Hiato de íons fortes e sua cinética de aclaramento como marcador da mortalidade em pacientes com choque séptico

Resumen: Introducción: Existe evidencia clínica de que la brecha de iones fuertes obtenida por el método de Stewart de equilibrio ácido-base es mejor predictora de mortalidad que los parámetros tradicionales en algunos pacientes críticamente enfermos. Objetivo: Evaluar la cinética de depuración de la brecha de iones fuertes en individuos con choque séptico durante las primeras 48 horas de estancia en la unidad de cuidados intensivos. Material y métodos: Se trata de un estudio retrospectivo observacional, con datos obtenidos del expediente clínico, realizado en una unidad de cuidados intensivos adultos en un hospital privado de la ciudad de Monterrey, Nuevo León. Se evaluaron variables demográficas, así como datos obtenidos de gasometrías y química sanguínea al ingreso, a las 24 y 48 horas posteriores, para calcular parámetros tradicionales del equilibrio ácido-base y los obtenidos por el método de Stewart. Se calculó también la cinética de eliminación de dichos parámetros para evaluar sus cambios a través del tiempo y su relación con la mortalidad. Resultados: Se estudiaron 91 personas con choque séptico entre junio de 2014 y junio de 2016, con una mortalidad de 28.6%. La depuración de lactato, brecha aniónica corregida y brecha de iones fuertes a 48 horas no fueron capaces de predecir mortalidad, aunque sí los niveles individuales de dichos parámetros a las 48 horas. El mejor predictor de mortalidad fue AGCOR a 48, con un área bajo la curva ROC de 0.71805, contrario a la brecha de iones fuertes (SIG por sus siglas en inglés) a 48 horas, con un área bajo la curva ROC de 0.67367. Conclusiones: Los cambios a través de las primeras 48 horas de la brecha de iones fuertes son asociados a mortalidad, pero no aportan mayor beneficio que los parámetros tradicionales en sujetos con choque séptico.

Abstract: Introduction: There is clinical evidence that the strong ion gap obtained by Stewart's acid-base approach is a better predictor of mortality than those obtained by the traditional approach in some critically ill patients. Objective: To evaluate the strong ion gap clearance kinetics in patients with septic shock during the first 48 hours in the intensive care unit. Material and methods: A retrospective, observational study obtained from a patient database in a private intensive care unit in Monterrey, Nuevo León. Patient's demographics were analyzed, along with data collected from their laboratory work at admission and at 24 and 48 hours to calculate traditional acid-base parameters and parameters obtained by the Stewart's method. Clearance at 48 hours was also calculated to track their changes over time and to evaluate their relation to patient mortality. Results: Data from 91 patients with septic shock admitted between June 2014 and June 2016 were studied, with a 28.6% mortality rate. Lactate clearance, corrected anion gap clearance and strong ion gap clearance at 48 hours were not related to patient mortality, although their individual values at 48 hours were able to predict mortality. The best predictor of mortality was AGCOR at 48, with an area under the ROC curve of 0.71805, compared with an area under the ROC curve of 0.67367 for SIG at 48 hours. Conclusions: Strong ion gap changes over the first 48 hours were associated with mortality; however, they do not offer any advantage over traditional acid-base parameters in patients with septic shock.

Resumo: Introdução: Existe evidência clínica que o hiato de íons fortes, obtido pelo método de Stewart de ácido-base, é melhor preditor de mortalidade que os parâmetros tradicionais em alguns pacientes graves. Objetivo: Avaliar a cinética de depuração do hiato de íons fortes em pacientes com choque séptico durante as primeiras 48 horas de estadia na unidade de terapia intensiva. Material e métodos: Um estudo retrospectivo, observacional com dados obtidos a partir do prontuário médico. Realizado na UTI de um hospital particular na cidade de Monterrey, em Nuevo León. Foram avaliadas as variáveis ​​demográficas e os dados obtidos a partir da gasometria e química sanguínea na admissão, 24 horas e 48 horas posteriores para calcular os parâmetros tradicionais do equilíbrio ácido-base e os obtidos pelo método de Stewart. Calculou-se também as cinéticas de eliminação destes parâmetros e assim avaliar as alterações ao longo do tempo e a sua relação com a mortalidade. Resultados: Foram estudados 91 pacientes com choque séptico entre junho de 2014 e junho de 2016, com uma taxa de mortalidade de 28.6%. A depuração de lactato, hiato aniônico corrigido e hiato de íons fortes às 48 horas não foram capazes de prever a mortalidade, se bem que previram os níveis individuais de estes parâmetros às 48 horas. O melhor preditor de mortalidade foi AGCOR às 48 com uma área sob a curva ROC de 0.71805, contrário ao SIG às 48 horas com uma área sob a curva ROC de 0.67367. Conclusões: As alterações através das primeiras 48 horas do hiato de íons fortes está associada com a mortalidade, mas não fornecem maior benefício que os parâmetros tradicionais em pacientes com choque séptico.

A Quick Reference on Anion Gap and Strong Ion Gap.

Metabolic acid-base disorders are common in emergency and critically ill patients. Clinicians may have difficulty recognizing their presence when multiple acid-base derangements are present in a single patient simultaneously. The anion gap and the strong ion gap concepts are useful calculations to identify the components of complex metabolic acid-base associated to the presence of unmeasured anions. This article presents their definition, normal values, indications, limitations, and guidelines for interpretation of changes in the clinical setting.

Chloride content of solutions used for regional citrate anticoagulation might be responsible for blunting correction of metabolic acidosis during continuous veno-venous hemofiltration.

BACKGROUND: Citrate, the currently preferred anticoagulant for continuous veno-venous hemofiltration (CVVH), may influence acid-base equilibrium. METHODS: The effect of 2 different citrate solutions on acid-base status was assessed according to the Stewart-Figge approach in two consecutive cohorts of critically ill adult patients. The first group received Prismocitrate 10/2 (PC10/2; 10 mmol citrate/L). The next group was treated with Prismocitrate 18/0 (PC18; 18 mmol citrate/L). Both groups received bicarbonate-buffered fluids in post-dilution. RESULTS: At similar citrate flow, the metabolic acidosis present at baseline in both groups was significantly attenuated in PC18 patients but persisted in PC10/2 patients after 24 h of treatment (median pH 7,42 vs 7,28; p = 0.0001). Acidosis in the PC10/2 group was associated with a decreased strong ion difference and an increased strong ion gap (respectively 43 vs. 51 mmol/L and 17 vs. 12 mmol/L, PC10/2 vs. PC18; both p = 0.001). Chloride flow was higher in PC10/2 than in PC18 subjects (25.9 vs 14.3 mmol/L blood; p < 0.05). CONCLUSION: Correction of acidosis was blunted in patients who received 10 mmol citrate/L as regional anticoagulation during CVVH. This could be explained by differences in chloride flow between the applied citrate solutions inducing hyperchloremic acidosis.

The prognostic value of the strong ion gap in acute pancreatitis.

PURPOSE: In this study, we aimed to evaluate the predictive value of Stewart-derived parameters for the development of severe type of acute pancreatitis (AP) and for AP-related mortality. METHODS: We studied 186 patients admitted to the hospital with AP. We performed blood gas and biochemical analysis for each patient on admission. We calculated multiple metrics according to the Stewart's acid-base theory and assessed their accuracy as predictors of AP severity and mortality. RESULTS: Of the 186 patients presenting with AP, 85 (45.7%) developed severe AP and 33 (17.7%) died during hospitalization. Patients with severe AP had significantly higher median strong ion gap (SIG) than did patients with mild or moderate AP (7.88 vs 2.11 mEq/L, P< .001). In multivariate logistic regression analysis, SIG had an odds ratio (OR) of 1.56 (P< .001). In addition, SIG had good predictive power for mortality (OR, 1.26; P= .014) as well as acute kidney injury (OR, 1.34; P< .001). CONCLUSIONS: In a cohort of patients with AP, SIG was a strong independent predictor of severity and mortality. Besides, SIG might also be an early marker for acute kidney injury in AP patients. Additional research is needed to identify the nature of the unmeasured anions responsible for such findings.

Physicochemical Approach to Determine the Mechanism for Acid-Base Disorders in 793 Hospitalized Foals.

BACKGROUND: The quantitative effect of strong electrolytes, unmeasured strong anions (UAs), pCO2, and plasma protein concentrations in determining plasma pH can be demonstrated using the physicochemical approach. Plasma anion gap (AG) and strong ion gap (SIG) are used to assess UAs in different species. HYPOTHESES: Strong ions are a major factor influencing changes in plasma pH of hospitalized foals. AG and SIG accurately predict severe hyper-L-lactatemia ([L-lac(-)] > 7 mmol/L). ANIMALS: Seven hundred and ninety three hospitalized foals < 7 days old. METHODS: Retrospective study. The relationship between measured pH and physicochemical variables, and the relationship between plasma [L-lac(-)] and AG and SIG, were determined using regression analyses. Optimal AG and SIG cut points to predict hyper-L-lactatemia were identified using an ROC curve analysis. RESULTS: Combined, the measured strong ion difference and SIG accounted for 54-69% of the changes in the measured arterial pH of hospitalized foals. AG and SIG were significantly associated with plasma [L-lac(-)] (P < .0001). The receiver operator characteristics (ROC) AUC of AG and SIG for prediction of severe hyper-L-lactatemia were 0.89 (95%CI, 0.8-0.95; P < .0001) and 0.90 (95%CI, 0.81-0.96; P < .0001), respectively. Severe hyper-L-lactatemia was best predicted by AG > 27 mmol/L (sensitivity 80%, 95%CI, 56-94, specificity 85%, 95%CI, 73-93; P < .0001) and SIG <-15 mmol/L (sensitivity 90%, 95%CI, 68-98; specificity 80%; 95%CI, 68-90; P < .0001). CONCLUSION AND CLINICAL RELEVANCE: Altered concentrations of strong ions (Na(+), K(+), Cl(-)) and UAs were the primary cause of acidemia of hospitalized foals. AG and SIG were good predictors of hyper-L-lactatemia and could be used as surrogate tests.

Has Stewart approach improved our ability to diagnose acid-base disorders in critically ill patients?

The Stewart approach-the application of basic physical-chemical principles of aqueous solutions to blood-is an appealing method for analyzing acid-base disorders. These principles mainly dictate that pH is determined by three independent variables, which change primarily and independently of one other. In blood plasma in vivo these variables are: (1) the PCO2; (2) the strong ion difference (SID)-the difference between the sums of all the strong (i.e., fully dissociated, chemically nonreacting) cations and all the strong anions; and (3) the nonvolatile weak acids (Atot). Accordingly, the pH and the bicarbonate levels (dependent variables) are only altered when one or more of the independent variables change. Moreover, the source of H(+) is the dissociation of water to maintain electroneutrality when the independent variables are modified. The basic principles of the Stewart approach in blood, however, have been challenged in different ways. First, the presumed independent variables are actually interdependent as occurs in situations such as: (1) the Hamburger effect (a chloride shift when CO2 is added to venous blood from the tissues); (2) the loss of Donnan equilibrium (a chloride shift from the interstitium to the intravascular compartment to balance the decrease of Atot secondary to capillary leak; and (3) the compensatory response to a primary disturbance in either independent variable. Second, the concept of water dissociation in response to changes in SID is controversial and lacks experimental evidence. In addition, the Stewart approach is not better than the conventional method for understanding acid-base disorders such as hyperchloremic metabolic acidosis secondary to a chloride-rich-fluid load. Finally, several attempts were performed to demonstrate the clinical superiority of the Stewart approach. These studies, however, have severe methodological drawbacks. In contrast, the largest study on this issue indicated the interchangeability of the Stewart and conventional methods. Although the introduction of the Stewart approach was a new insight into acid-base physiology, the method has not significantly improved our ability to understand, diagnose, and treat acid-base alterations in critically ill patients.