Correction of the anion gap for albumin in order to detect occult tissue anions in shock

Increased serum albumin corrected anion gap levels are associated with poor prognosis in septic patients with liver cirrhosis

The prognosis of septic patients with cirrhosis is worse compared to septic patients without cirrhosis. Early and accurate prognosis determination in patients with cirrhosis and sepsis is pivotal for guiding treatment decisions. The aim of this study was to investigate the association between albumin-corrected anion gap (ACAG) and clinical prognosis of patients with sepsis and cirrhosis. This study extracted data of patients with sepsis and cirrhosis from the Medical Information Mart for Intensive Care (MIMIC-IV) database. A total of 1340 patients (64.6% male) were enrolled. After confounders adjusting, elevated ACAG had a significant association with 28-day mortality (HR1.604; 95% CI 1.258-2.048; P < 0.001). Restricted cubic spline revealed that a linear relationship between ACAG and 28-day mortality (P-nonlinear = 0.089, P-overall = 0.001). According to the ROC curve analysis, the ACAG demonstrated a higher area under the curve (AUC) of 0.703 compared to AG (0.675). Kaplan-Meier analysis revealed higher 28-day mortality in high ACAG group (log-rank test, χ^2 = 175.638, P < 0.001). Furthermore, subgroup analysis showed a significant interaction between ACAG and etiology of cirrhosis (P for interaction = 0.014). Therefore, ACAG could provide clinicians with valuable insights for guiding interventions in this high-risk population.

Albumin corrected anion gap for predicting in-hospital death among patients with acute myocardial infarction: A retrospective cohort study

OBJECTIVE

To explore the relationship between Anion Gap (AG), Albumin Corrected AG (ACAG), and in-hospital mortality of Acute Myocardial Infarction (AMI) patients and develop a prediction model for predicting the mortality in AMI patients.

METHODS

This was a retrospective cohort study based on the Medical Information Mart for Intensive Care (MIMIC)-Ⅲ, MIMIC-IV, and eICU Collaborative Study Database (eICU). A total of 9767 AMI patients who were admitted to the intensive care unit were included. The authors employed univariate and multivariable cox proportional hazards analyses to investigate the association between AG, ACAG, and in-hospital mortality; p < 0.05 was considered statistically significant. A nomogram incorporating ACAG and clinical indicators was developed and validated for predicting mortality among AMI patients.

RESULTS

Both ACAG and AG exhibited a significant association with an elevated risk of in-hospital mortality in AMI patients. The C-index of ACAG (C-index = 0.606) was significantly higher than AG (C-index = 0.589). A nomogram (ACAG combined model) was developed to predict the in-hospital mortality for AMI patients. The nomogram demonstrated a good predictive performance by Area Under the Curve (AUC) of 0.763 in the training set, 0.744 and 0.681 in the external validation cohort. The C-index of the nomogram was 0.759 in the training set, 0.756 and 0.762 in the validation cohorts. Additionally, the C-index of the nomogram was obviously higher than the ACAG and age shock index in three databases.

CONCLUSION

ACAG was related to in-hospital mortality among AMI patients. The authors developed a nomogram incorporating ACAG and clinical indicators, demonstrating good performance for predicting in-hospital mortality of AMI patients.

Association between the anion-gap and 28-day mortality in critically ill adult patients with sepsis: A retrospective cohort study

Metabolic acidosis is usually associated with the severity of the condition of patients with sepsis or septic shock. Serum anion gap (AG) is one of the indicators of response metabolism. This study was performed to investigate whether the initial serum AG is associated with the 28-day mortality in critically ill adult patients with sepsis. This retrospective cohort study, a total of 15,047 patients with confirmed Sepsis disease from 2008 to 2019 from the Medical Information Mart for Intensive Care IV (MIMIC-IV) v1.0 database. The MIMIC-IV database is a comprehensive, de-identified clinical dataset originating from the Beth Israel Deaconess Medical Center in Boston, it includes extensive data on intensive care unit (ICU) patients, such as vital signs, lab results, and medication orders, spanning multiple years, accessible to researchers through an application process. AG can be obtained by direct extraction in the MIMIC-IV database (itemid = 50,868 from the laboratory events table of mimic_hosp), inclusion of AG values for the first test on first day of ICU admission. The patients were grouped into quartiles according to the AG interquartile range. The primary outcome was the 28-day mortality. Multiple logistic regression analysis was used to calculate the odds ratio (OR), while accounting for potential confounders, and the robustness of the results were evaluated in subgroup analyses. Among the 15,047 patients included in this study, the average age was 65.9 ± 16.0 years, 42.5% were female, 66.1% were Caucasian, and the 28-day mortality rate was 17.9% (2686/15,047). Multiple logistic regression analysis revealed the 28-day mortality in every increase of AG (per SD mEq/L), there is an associated 1.2 times (OR 1.2, 95% CI 1.12-1.29, P < .001) increase. Increased 28-day mortality (OR 1.53, 95% confidence interval 1.29-1.81, P < .001) in the group with the AG (15-18 mEq/L), and (OR 1.69, 95% confidence interval 1.4-2.04, P < .001) in the group with the highest AG (≥18 mEq/L), AG (<12 mEq/L) as a reference group, in the fully adjusted model. In adult patients with sepsis, the early AG at the time of ICU admission is an independent risk factor for prognosis.

Independent variables of pH: Ten Knights of the Hydrogen Ion Kingdom-Part I. A prospective observational study

CO2, HCO3, SID, and total weak acids have been defined as pH's independent variables. However, according to Gamble, HCO3 should be equal to the difference between the sum of cations and the sum of anions besides HCO3. Therefore, if this mathematical expression is substituted for HCO3 in the Henderson-Hasselbalch equation, all independent variables of pH can be demonstrated. Our aim is to test this theory in this study. This prospective observational study was conducted between 2019 and 2020. All admitted patients to the intensive care unit who were >18 years old were included. Demographic data, blood gas parameters, albumin, magnesium, and inorganic phosphorus levels, and outcomes were recorded twice (at admission and at the 24th hour). The multivariate linear regression model was used to determine pH's independent variables. In the multivariate linear regression model, pH was significantly increased by each unit increase in Na, K, Ca, and Mg (mmol L-1). In contrast, pH was significantly decreased by each unit increase in CO2, Cl, lactate, albumin (g dL-1), inorganic phosphorus (mg dL-1), and the strong ion gap. Ten independent variables can accurately predict the changes in pH. For this reason, all ten independent variables should be separately evaluated when interpreting the acid-base status. With this understanding, all algorithms regarding acid-base evaluation may become unnecessary.

The correlation between albumin-corrected anion gap and prognosis in patients with acute myocardial infarction

AIMS

Acute myocardial infarction (AMI) is a cardiovascular disease with high morbidity and mortality. We collected patients with AMI from the Medical Information Mart for Intensive Care IV (v2.0) database and explored the association between serum albumin-corrected anion gap (ACAG) level and mortality in patients with AMI.

METHODS AND RESULTS

Data of adult patients with AMI were collected. According to the 360 day prognosis, patients were divided into survival and non-survival groups. Based on the ACAG level, patients were then divided into normal and high ACAG groups. Cox hazard proportional models and restricted cubic splines (RCSs) were used to investigate the correlation between ACAG and mortality. Kaplan-Meier curves were created to compare the cumulative survival rates between the high and normal ACAG groups. The receiver operating characteristic (ROC) curve was used to analyse the predictive value of ACAG for the prognosis of patients with AMI. Sensitivity and subgroup analyses were conducted to revalidate the results. Finally, 1783 patients were included. Elevated ACAG (>20 mmol/L) was significantly associated with 30 and 360 day mortality (P < 0.001). Adjusted for multiple confounding factors, the Cox proportional hazard analysis showed that elevated ACAG (>20 mmol/L) was an independent risk factor of increased all-cause mortality in patients with AMI (hazard ratio 1.423, 95% confidence interval 1.206-1.678, P < 0.001). RCS analysis further showed that there was a non-linear trend relationship between ACAG and the risk of all-cause mortality at 30 and 360 days (χ2 = 10.750, P = 0.013; χ2 = 13.960, P = 0.003). Kaplan-Meier survival curves showed that the 30 and 360 day cumulative survival rates of patients with AMI were significantly lower (log-rank test, χ2 = 98.880, P < 0.001; χ2 = 105.440, P < 0.001) in the high ACAG group. ROC curve analysis showed that the area under the curve (AUC) of ACAG was 0.651, while the AUC of anion gap (AG) was 0.609, indicating that ACAG had a higher predictive value for 360 day mortality than AG. When combined with Sequential Organ Failure Assessment score, the predictive performance of ACAG for 360 day mortality was better, with an AUC of 0.699. Sensitivity and subgroup analyses were conducted suggesting the stability of our results.

CONCLUSIONS

Elevated serum ACAG (≥20 mmol/L) is an independent risk factor for short-term and long-term mortality in critically ill patients with AMI, and it may assist clinicians and nurses identifying high-risk patients.

Association between albumin-corrected anion gap and in-hospital mortality of intensive care patients with trauma: A retrospective study based on MIMIC-Ⅲ and Ⅳ databases

BACKGROUND

To investigate the correlation between albumin-corrected anion gap(ACAG) within the first 24 hours of admission and in-hospital mortality in trauma patients in intensive care unit(ICU).

MATERIALS AND METHODS

We utilized the MIMIC-Ⅲ and MIMIC-Ⅳ databases to examine trauma patients admitted to the ICU. The relationship between ACAG and in-hospital mortality in trauma patients was analyzed using Receiver Operating Characteristic(ROC) curve, Kaplan-Meier (K-M) survival curve, and Cox regression model. Propensity score matching (PSM) and subgroup analysis were conducted to enhance stability and reliability of the findings. Mortality at 30-day and 90-day served as secondary outcomes.

RESULTS

The study enrolled a total of 1038 patients. The AUC for ACAG (0.701, 95%CI: 0.652-0.749) was notably higher than that for anion gap and albumin. The Log-rank test revealed that the optimal cut-off point of ACAG for predicting in-hospital mortality was determined to be 20.375mmol/L. The multivariate Cox regression analysis demonstrated an independent association between high ACAG level and a higher risk of in-hospital mortality (HR = 3.128, 95% CI: 1.615-6.059). After PSM analysis, a matched cohort consisting of 291 subjects was obtained. We found no signifcant interaction in most stratas. Finally, The in-hospital, 30-day, and 90-day survival rates in the high ACAG group exhibited a statistically decrease compared to those in the low ACAG group both pre- and post-matching.

CONCLUSION

The elevated level of ACAG was found to be independently associated with increased in-hospital mortality among trauma patients in the ICU.

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.

Relationship between anion gap and in-hospital mortality in intensive care patients with liver failure: a retrospective propensity score matching analysis

OBJECTIVES

To elucidate the association between anion gap (AG) and in-hospital mortality in intensive care patients with liver failure.

METHODS

Demographic and clinical characteristics of intensive care patients with liver failure in the Medical Information Mart for Intensive Care-IV (MIMIC-IV) database were collected, and binomial logistic and Cox regression was conducted to investigate the association between AG and in-hospital mortality. The area under the receiver operating characteristic (ROC) curve (AUC) was conducted to characterize the performance of AG in predicting in-hospital mortality, and was compared with the albumin corrected anion gap (ACAG) and the End-Stage Liver Disease (MELD) score. The Kaplan-Meier curve was plotted for in-hospital survival analysis of AG and patients with liver failure. The propensity score matching (PSM) analysis was performed to mitigate selection bias.

RESULTS

AG was an independent risk factor for in-hospital mortality in intensive care patients with liver failure. Before PSM, the AUCs of AG, ACAG, and MELD were 0.666, 0.682, and 0.653, respectively. After PSM, the AUCs of AG, ACAG, and MELD scores were 0.645, 0.657, and 0.645, respectively, and there is no difference in the predictive performance of the three indicators upon comparison. Compared with the low-AG (≤20 mmol/L) group, the hazard ratio (HR) for in-hospital death of the high-AG (>20 mmol/L) group was determined to be 2.1472 (before PSM)/1.8890 (after PSM).

CONCLUSIONS

AG is associated with in-hospital mortality in intensive care patients with liver failure and demonstrates a moderate predictive value, which is comparable to the predictive power of the MELD score. AG may serve as an indirect marker of in-hospital mortality of patients with liver failure by reflecting the degree of metabolic acidosis.

Association between albumin corrected anion gap and all-cause mortality in critically ill patients with acute kidney injury: a retrospective study based on MIMIC-IV database

BACKGROUND

The early identification of patients at high risk for acute kidney injury (AKI) with a poor prognosis is crucial to prevent complications and minimize mortality. This study sought to investigate the association between albumin-corrected anion gap (ACAG) and all-cause mortality among critically ill patients with AKI.

METHODS

All eligible AKI patients from the Medical Information Mart for Intensive Care IV (MIMIC-IV version 2.0) database were considered for participation in this study. We employed Kaplan-Meier curves to assess the 30-d and 360-d cumulative survival rates among various groups. Flexibly visualizing the connection between ACAG and mortality, we utilize restricted cubic splines (RCS) and multivariate Cox regression models. Result robustness underwent assessment through subgroup analyses and sensitivity analyses. Receiver-operating characteristic (ROC) curves were generated to evaluate the predictive performance of ACAG.

RESULTS

The study included 9625 AKI participants, of whom 58.60% were male, and the 360-d all-cause mortality rate was 39.89%. According to Kaplan-Meier analysis, the 30-d and 360-d cumulative survival rates for AKI patients were significantly lower in the high ACAG group than in the normal ACAG group. RCS analysis indicated that ACAG levels had a non-linear correlation with the risk of 30-d and 360-d mortality for AKI patients. Cox regression analysis demonstrated that ACAG is an independent risk indicator for 30-d and 360-d prognosis in AKI patients in the ICU.

CONCLUSIONS

Elevated ACAG levels (> 20 mmol/L) at ICU admission were associated with 30-d and 360-d all-cause mortality in critically ill patients with AKI.

Role of Albumin-corrected Anion Gap and Lactate Clearance in Predicting Mortality in Pediatric Intensive Care Patients

Background

Identifying mortality risk in critically ill children is central to diagnostic and treatment practices. For this purpose, scoring systems, such as the Pediatric Index of Mortality 3 (PIM 3), have been proposed; however, the role of biochemical markers, such as albumin-corrected anion gap (cAG) and lactate clearance (LC), in predicting mortality in pediatric intensive care unit (PICU) patients is yet to be explored.

Aims

To evaluate the predictive value of the cAG and LC for mortality in pediatric patients admitted to a PICU.

Study Design

Retrospective single-center cohort study.

Methods

Clinical and laboratory data from the time of PICU admission were collected, and patients were classified into based on their 0- and 6-hour of admission lactate levels into an LC(+) group (patients with normal or decreasing lactate levels) or an LC(−) group (increasing lactate levels). LC and cAG levels were compared using the Mann-Whitney U test and Student’s t-test, respectively. Additionally, multiple logistic regression analysis was performed to evaluate the effect of LC and cAG on mortality.

Results

We included 825 patients in the study; the mortality rate was 8.6%. The absence of LC [adjusted odds ratio (AOR) =4.735; 95% confidence interval (CI): 2.163-10.367; p < 0.001], cAG (AOR =1.064; 95% CI: 1.010-1.122; p = 0.019) and PIM 3 (AOR = 1.871; 95% CI: 1.553-2.254; p < 0.001) were independent risk factors for mortality. Using the receiver operating characteristic curve analysis of PIM 3 as a predictor of mortality, area under the curve values of 0.832 (95% CI: 0.805-0.857; p < 0.001) for the original score and 0.858 for a revised PIM 3 score (based on the β coefficients obtained for cAG and LC; 95% CI 0.832-0.881; p < 0.001) were obtained, which was significantly different (p = 0.027).

Conclusion

A cAG value > 18 at the time of PICU admission high lactate levels which do not decrease within 6 hours of hospitalization are associated with an increased risk of mortality. The revised PIM 3 score, which includes cAG and LC, is a better predictor of mortality than the classical PIM 3 score.

The relationship between albumin corrected anion gap levels and mortality in patients with asthma in the ICU

Although previous studies have suggested that albumin-corrected anion gap (ACAG) may be a predictor of mortality in critically ill patients in intensive care unit (ICU), its utility in the context of asthma has not been definitively established. In this study, baseline data, albumin concentration, anion gap (AG) and 30-d mortality data were retrieved from the Medical Information Mart for Intensive Care IV database (MIMIC-IV) for patients with asthma in the intensive care unit. Receiver operating characteristic (ROC) curves were constructed to analyze the predictive ability of ACAG and AG. The risk of 30-day mortality among patients with ACAG and asthma was analyzed using a restricted cubic spline (RCS) plot. Decision curve analysis (DCA) was used to evaluate the clinical usefulness of ACAG as a prognostic factor for 30-day mortality. Subsequently, subgroup analysis was conducted to explore potential variations in the relationship between ACAG and 30-day mortality based on factors such as sex, age, whether the asthma was acute, and other co-morbidities. Our study reveals that ACAG is a significant independent predictor of 30-day mortality in asthmatic patients receiving intensive care. The area under the AUC curve for ACAG was found to be 0.703, which is higher than that of AG, indicating that ACAG has a better predictive ability for 30-day mortality in this population. Furthermore, higher levels of ACAG were found to be associated with increased risk of 30-day mortality in asthmatic patients. In addition, decision curve analysis (DCA) demonstrated that the net benefit of ACAG was greater than that of AG. These findings suggest that ACAG may be a valuable prognostic factor for predicting 30-day mortality in asthmatic patients in the ICU. Our study provides evidence that ACAG is associated with an increased risk of 30-d mortality and has better predictive value in patients with combined asthma who are admitted to the ICU than AG.

Relationship Between Albumin-Corrected Anion Gap and Mortality in Hospitalized Heart Failure Patients

BACKGROUND

Heart failure (HF) is a disease with high morbidity and mortality. Despite the efforts to reduce mortality rates through medical progress, it is necessary to develop markers to identify critically ill patients. In our study, we aimed to investigate the relationship between albumin-corrected anion gap (ACAG) and mortality in hospitalized patients with HF.

METHODOLOGY

We performed a retrospective study that included patients with HF hospitalized in the Erzurum City Hospital between 2015 and 2022. The basal clinical, hematological, and biochemical findings of the patients were obtained from the electronic medical records. ACAG was calculated. The date and causes of death of the patients were searched and recorded through the Republic of Türkiye Ministry of Health Death Notification System (ÖBYS) and Central Population Administration System (MERNIS). Thus, the relationship between ACAG and mortality in hospitalized patients with HF was evaluated.

RESULTS

A total of 205 patients hospitalized for HF were included in the study. The mean age of all people in this study was 71.8 ± 10.7 years. A total of 104 (50.7%) of the patients included in the study were women. The mean left ventricular ejection fraction was 47.2 ± 13.6%. The mean follow-up period of the entire population was 76.5 ± 18.9 months. The mortality rate was 11.7% (24 patients). Serum anion gap (SAG) and ACAG were significantly higher in the group with death outcomes (p = 0.043 and p = 0.012, respectively). Cox regression analysis showed that ACAG was an independent predictor of HF mortality (p = 0.003). ACAG area under the curve was 0.773 (95% CI 0.634 - 0.914), the cut-off was 13, sensitivity was 75%, and specificity was 75.9% (p = 0.002).

CONCLUSION

Statistical analysis showed a meaningful connection between an increase in ACAG and mortality in hospitalized patients with HF. Consequently, ACAG can be used as an independent predictor of mortality in patients with HF.

Association between albumin corrected anion gap and 30-day all-cause mortality of critically ill patients with acute myocardial infarction: a retrospective analysis based on the MIMIC-IV database

BACKGROUND

The anion gap (AG) has been linked to the prognosis of many cardiovascular disorders. However, the correlation between albumin-corrected anion gap (ACAG) and 30 d all-cause mortality of intensive care patients with acute myocardial infarction (AMI) is unclear. Furthermore, owing to the lack of studies, it is also unknown whether ACAG is more accurate than AG in predicting the mortality of AMI.

METHODS

The Medical Information Mart for Intensive Care IV (MIMIC IV) dataset was used to provide patient data in this retrospective cohort study. ACAG is computed using the formulae: [4.4-{albumin (g/dl)}] × 2.5 + AG. The primary outcome was 30 d all-cause mortality intensive care patients with AMI. To explore the prognostic worthiness of ACAG, the receiver operating characteristic curve, smooth curve fitting, Cox regression model, and Kaplan survival analysis was performed.

RESULTS

We enrolled 2,160 patients in this study. ACAG had a better predictive value for 30 d all-cause mortality than AG, with an area under the curve of 0.66. The association between ACAG levels and overall mortality was nonlinear. In our model, after correcting for confounding factors, the ACAG was the independent predictor for 30 d all-cause mortality (HR 1.75, 95%CI 1.24, 2.47). ACAG K-M estimator curve analyses revealed that the group with ACAG ≥ 21.75 mmol/l had poor survival rate than the other group.

CONCLUSIONS

High serum ACAG levels were a significant risk factor for 30 d all-cause mortality in critically ill patients with AMI. ACAG concentration and 30 d all-cause mortality had a nonlinear relationship. ACAG had better predictive value in identifying 30 d all-cause mortality of patients with AMI in ICU than the AG.

Elevated albumin corrected anion gap is associated with poor in-hospital prognosis in patients with cardiac arrest: A retrospective study based on MIMIC-IV database

Background

Cardiac arrest(CA) is one of the most leading causes of death. Most of the indicators which used to predict the prognosis of patients with CA are not recognized. Previous studies have suggested that albumin corrected anion gap (ACAG) is associated with recovery of spontaneous circulation in patients with CA, but the predictive value of ACAG for prognosis has not been investigated. This study aims to explore the relationship between ACAG and prognosis during hospitalization in patients with CA.

Methods

The baseline data of adult patients with CA hospitalized in the intensive care unit (ICU) from 2008 to 2019 in the American Intensive Care Database (MIMIC-IV, version v2.0) were collected. According to the in-hospital prognosis, patients were divided into survival and non-survival group. Based on the criteria of ACAG level in the previous literature, patients enrolled were divided into normal ACAG (12-20 mmol/L) and high ACAG (>20 mmol/L) group. The basic information of patients during hospitalization were compared and analyzed between the two groups with propensity score matching (PSM). The Kaplan-Meier method was used to compare the cumulative survival rates of normal ACAG and high ACAG groups before and after matching. Restricted cubic spline (RCS) method and multivariate COX proportional hazards regressions were used to analyze whether elevated ACAG was associated with all-cause mortality during hospitalization.

Results

A total of 764 patients were included. A matched cohort (n = 310) was obtained after PSM analysis. The mortality rate before and after matching in the high ACAG group was higher than that in the normal ACAG group (χ ² = 25.798; P < 0.001; χ ² = 6.258; P = 0.012) The Kaplan-Meier survival analysis before and after matching showed that the cumulative survival rate of the high ACAG group was lower (P < 0.05). RCS analysis showed that ACAG had a non-linear relationship with the risk of in-hospital all-cause mortality (χ ² = 6.060, P < 0.001). Multivariate COX regression analysis before and after PSM suggested that elevated ACAG was an independent risk factor for all-cause mortality in patients with CA during hospitalization (P < 0.01).

Conclusions

Elevated ACAG is associated with increased all-cause mortality in patients with CA during hospitalization, it can be an independent risk factor for poor prognosis in patients with CA and remind clinicians to pay more attention to these patients.

Diabetic ketoacidosis

Diabetic ketoacidosis (DKA) is a form of a hyperglycemic emergency mainly characterized by the triad of hyperglycemia, ketosis, and anion gap metabolic acidosis. DKA may be the initial presentation in approximately 25-40 % of patients with type 1 diabetes. It may also occur in at least 34% of patients with type 2 diabetes. DKA has economic as well as medical implications. This review aims to explore and discuss diabetic ketoacidosis, its pathophysiology, clinical presentation, diagnosis, and management, including nuances in special populations such as pediatrics, obstetrics, and patients with chronic kidney disease.

Anion gap physiology and faults of the correction formula

DISCLAIMER

In an effort to expedite the publication of articles, AJHP is posting manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time.

PURPOSE

The anion gap is a calculated fundamental laboratory parameter used to identify and monitor acid-base disturbances. A recently popularized correction formula transforms the resulting integer to compensate for hypoalbuminemia and improve diagnostic yield. Clinical pharmacists should be aware of the underlying biochemistry, interpretation, and limitations of this formula to discern drug- and disease-related etiologies.

SUMMARY

The anion gap is utilized in most care settings, ranging from outpatient monitoring to inpatient intensive care units. Supported by decades of experience, the original anion gap derives its value from its simplicity. Applying the anion gap in metabolic acidosis can help narrow differential diagnosis and detect concomitant acid-base disorders. To account for hypoalbuminemia and potential missed diagnoses, a correction formula was developed to improve sensitivity. Yet, the law of electroneutrality ensures that hypoalbuminemia is already accounted for in the original anion gap, and the proposed correction formula was derived from samples unrepresentative of human physiology. Evidence from clinical trials shows no benefit from applying the correction formula.

CONCLUSION

There is no advantage to correcting the anion gap, and such correction may increase the risk of misinterpretation or error. Clinicians should understand these limitations when diagnosing or trending acid-base disturbances.

Plasma Anion Gap and Risk of In-Hospital Mortality in Patients with Acute Ischemic Stroke: Analysis from the MIMIC-IV Database

We aimed to investigate the association between the plasma anion gap (AG) and in-hospital mortality among patients with acute ischemic stroke (AIS). In total, 1236 AIS patients were enrolled using the Medical Information Mart for Intensive Care Database IV. Primary outcome was in-hospital mortality. The patients were divided into four groups according to AG category. The mean age and Charlson comorbidity index increased as the AG category increased. The fourth AG category was most related to the in-hospital mortality (hazards ratio (HR), 95% confidence interval (CI): 2.77, 1.60-4.71), even after adjusting for possible confounding variables (Model 1: HR, 95% CI: 3.37, 1.81-6.09; Model 2: HR, 95% CI: 3.57, 1.91-6.69). Moreover, intensive care unit mortality (p = 0.008) was higher in the highest AG category, but the intracranial hemorrhage (p = 0.071) did not associate with the plasma AG. The plasma AG had a satisfactory predictive ability for in-hospital mortality among AIS patients (areas under the receiver operating characteristic curve: 0.631). The plasma AG is an independent risk factor that can satisfactorily predict the in-hospital mortality among AIS patients.

Albumin corrected anion gap for predicting in-hospital mortality among intensive care patients with sepsis: A retrospective propensity score matching analysis

BACKGROUND

The relationship between albumin corrected anion gap (ACAG) and in-hospital mortality of intensive care sepsis patients is currently inconclusive.

METHODS

The baseline data, concentration of albumin, anion gap (AG), ACAG and in-hospital prognosis of intensive care patients with sepsis were retrieved from the Medical Information Mart for Intensive Care IV database. Propensity score matching (PSM) analysis was performed to reduce bias. Receiver operating characteristic curves were drawn for albumin, AG, and ACAG, and comparisons between the areas under the ROC curves were conducted. Decision curve analysis (DCA) was performed to determine the net benefit of ACAG.

RESULTS

ACAG was related to in-hospital mortality in intensive care patients with sepsis. The AUCs of ACAG were 0.689 (before PSM) and 0.644 (after PSM), which were significantly higher than that of albumin or AG. The Youden's index of ACAG was the highest, and the net benefit range of ACAG was also the largest according to the DCA.

CONCLUSIONS

ACAG has the highest predictive value for in-hospital mortality of intensive care patients with sepsis, which is better than albumin and AG. Using ACAG to predict the in-hospital mortality to guide clinical applications may obtain the highest net benefit.

Diagnostic utility of different models used to assess the acid-base balance in cats with chronic kidney disease

Metabolic acidosis is diagnosed based on the concentration of bicarbonate ions and partial pressure of carbon dioxide in arterial blood, although acid-base balance (ABB) disorders may also be diagnosed based on the serum ion concentrations in order to determine the values of strong ion difference (SID), anion gap (AG), corrected anion gap (AGcorr) and chloride/sodium ratio (Cl-/Na+). The aim of this study was to assess and compare the classic model, the value of the AG, AGcorr, and Cl-/Na+ in the diagnosis of ABB disorders in cats with chronic kidney disease (CKD). The study group consisted of 80 cats with CKD, divided into four groups based on the guidelines of the International Renal Interest Society (IRIS). The control group (C) included 20 healthy cats. Metabolic acidosis - diagnosed based on the classic model (Hendersson-Hasselbalch equation) - was found in IRIS group IV. AG, AGcorr, SID calculated for IRIS groups II, III and IV were lower than in group C, while the value of AGdiff and Cl-/Na+ in those groups was higher than in group C. We can conclude that ABB analysis using the classic model enabled the detection of ABB disorders in cats in stage IV CKD. However, the analysis of the AG, AGcorr and Cl-/Na+ values enabled the diagnosis of acid-base balance disorders in cats with IRIS stage II, III and IV CKD.

Acid/base alterations during major abdominal surgery: 6% hydroxyethyl starch infusion versus 5% albumin

BACKGROUND

To compare the effects of intraoperative infusions of balanced electrolyte solution (BES)-based hydroxyethyl starch (HES) and saline-based albumin on metabolic acidosis and acid/base changes during major abdominal surgery conducted using Stewart's approach.

METHODS

Forty patients, aged 20-65 years, undergoing major abdominal surgery, were randomly assigned to the HES group (n = 20; received 500 ml of BES-based 6% HES 130/0.4) or the albumin group (n = 20; received 500 ml of normal saline-based 5% albumin). Acid-base parameters were measured and calculated using results obtained from arterial blood samples taken after anesthesia induction (T1), 2 hours after surgery commencement (T2), immediately after surgery (T3), and 1 hour after arriving at a postanesthetic care unit (T4).

RESULTS

Arterial pH in the HES group was significantly higher than that in the albumin group at T3 (7.40 ± 0.04 vs. 7.38 ± 0.04, P = 0.043), and pH values exhibited significant intergroup difference over time (P = 0.002). Arterial pH was significantly lower at T3 and T4 in the HES group and at T2, T3, and T4 in the albumin group than at T1. Apparent strong ion difference (SIDa) was significantly lower at T2, T3, and T4 than at T1 in both groups. Total plasma weak nonvolatile acid (ATOT) was significantly lower in the HES group than in the albumin group at T2, T3 and T4 and exhibited a significant intergroup difference over time (P < 0.001).

CONCLUSIONS

BES-based 6% HES infusion was associated with lower arterial pH values at the end of surgery than saline-based 5% albumin infusion, but neither colloid caused clinically significant metabolic acidosis (defined as an arterial pH < 7.35).

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.

Drug-induced acid-base disorders

The incidence of acid-base disorders (ABDs) is high, especially in hospitalized patients. ABDs are often indicators for severe systemic disorders. In everyday clinical practice, analysis of ABDs must be performed in a standardized manner. Highly sensitive diagnostic tools to distinguish the various ABDs include the anion gap and the serum osmolar gap. Drug-induced ABDs can be classified into five different categories in terms of their pathophysiology: (1) metabolic acidosis caused by acid overload, which may occur through accumulation of acids by endogenous (e.g., lactic acidosis by biguanides, propofol-related syndrome) or exogenous (e.g., glycol-dependant drugs, such as diazepam or salicylates) mechanisms or by decreased renal acid excretion (e.g., distal renal tubular acidosis by amphotericin B, nonsteroidal anti-inflammatory drugs, vitamin D); (2) base loss: proximal renal tubular acidosis by drugs (e.g., ifosfamide, aminoglycosides, carbonic anhydrase inhibitors, antiretrovirals, oxaliplatin or cisplatin) in the context of Fanconi syndrome; (3) alkalosis resulting from acid and/or chloride loss by renal (e.g., diuretics, penicillins, aminoglycosides) or extrarenal (e.g., laxative drugs) mechanisms; (4) exogenous bicarbonate loads: milk-alkali syndrome, overshoot alkalosis after bicarbonate therapy or citrate administration; and (5) respiratory acidosis or alkalosis resulting from drug-induced depression of the respiratory center or neuromuscular impairment (e.g., anesthetics, sedatives) or hyperventilation (e.g., salicylates, epinephrine, nicotine).

Strong ion gap is associated with mortality in pediatric burn injuries

Severe burn injury produces significant tissue damage, resulting in metabolic acidosis. Current methods of acid-base evaluation are based on dependent variables that may not be accurate after burn injury. The strong ion method of acid-base evaluation is based on independent variables and may accurately predict outcomes in severely burn-injured patients. The authors hypothesize that an increased strong ion gap present on admission will be associated with mortality in severely burn-injured pediatric patients. A retrospective chart review was performed of burn-injured pediatric patients with a TBSA 20% or greater. Data collected included age, TBSA burn injury, mechanism of injury, survival, ventilator days, hospital length of stay, intensive care unit length of stay, and admission laboratory values. Apparent and effective strong ion difference (SIDa, SIDe) were calculated. The strong ion gap (SIG) was determined as the difference between SIDa and SIDe. A total of 48 patients were included in the study. Mean age (years) and TBSA were 7.9 ± 0.8 years and 56.8 ± 2.6%. Eleven patients (23%) died. Mean TBSA for survivors (54.2 ± 2.9%) did not significantly differ from that of nonsurvivors (65.7 ± 5.34%). Ten patients suffered inhalation injury, which was associated with an odds ratio of 10.1* for mortality. Mean SIDa was 44.2 ± 3.2 for the entire study population. Survivors had a significantly lower SIDa (36.6 ± 0.5) than nonsurvivors (59.7 ± 13*). Mean SIDe for all patients was (25 ± 0.7) and did not differ significantly between survivors (24.7 ± 0.7) and nonsurvivors (25.8 ± 2). SIG for nonsurvivors (33.91 ± 14*) was significantly higher than for survivors (14.9 ± 0.3). Controlling for both TBSA and inhalation injury, death was associated with both an increased SIDa (B = 19.3*) and SIG (B = 17.3*). SIG is increased in severely burn-injured pediatric patients, indicating the presence of metabolic acidosis. Furthermore, an increased SIG is significantly associated with mortality. (*P <.05.).

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.

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 (A_tot). 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 A_tot 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.

Study on the Effectiveness of Cardiopulmonary Resuscitation in Elderly Patients Presenting with Cardiopulmonary Arrest on Arrival

OBJECTIVE

This study was conducted to determine whether a policy of not attempting to resuscitate patients who are 80 years of age and older with cardiopulmonary arrest on arrival is justifiable.

METHODS

The protocol of this study was approved without the need for informed consent by the research ethics board of Gunma University Hospital. We prospectively analyzed patients with cardiopulmonary arrest on arrival that was due to an intrinsic reason who were taken to Gunma University Hospital between January 2013 and March 2014. The patients were divided into two groups: patients who were less than 80 years of age (L group) and those aged 80 years and older (H group). We compared the patients' characteristics, including the etiology of cardiac arrest, and the prognosis between the two groups.

RESULTS

A total of 103 patients with cardiopulmonary arrest on arrival were enrolled. There were no significant differences in the patients' characteristics, such as age, sex, witness and bystander cardiopulmonary resuscitation, and transportation time between the two groups. The return of spontaneous circulation was obtained in 14 patients (25.5%) in the L group and in 9 patients (18.8%) in the H group; however, no significant difference was seen between the two groups. Two patients in the L group were in good neurological condition when they were discharged; however, the other patients did not survive.

CONCLUSION

Even patients 80 years of age and older can be resuscitated to spontaneous circulation. We do not endorse a policy that recommends not performing cardiopulmonary resuscitation based solely on the age of the patient.

Usefulness of serum fibrin degradation products and D-dimer levels as biomarkers to predict return of spontaneous circulation in patients with cardiopulmonary arrest on arrival: comparison with acid-base balance

Aim

We evaluated the usefulness of fibrin degradation products and D-dimer levels in blood to predict return of spontaneous circulation in patients with cardiopulmonary arrest on arrival compared with anion gap and albumin-corrected anion gap.

Methods

We retrospectively reviewed the medical records of patients with cardiopulmonary arrest on arrival who had been transferred to the emergency department of our hospital in 2012. Patients were divided into two groups: patients with return of spontaneous circulation (ROSC(+) group), and those without (ROSC(-) group). The levels of anion gap, albumin-corrected anion gap, fibrin degradation products and D-dimer measured on arrival were compared between the two groups.

Results

Fifty-three patients could be analyzed. The anion gap and albumin-corrected anion gap levels were significantly better in the ROSC(+) group than in the ROSC(-) group (anion gap, 28.7 mmol/L [median] versus 39.1 mmol/L; albumin-corrected anion gap, 31.1 mmol/L versus 40.9 mmol/L). The fibrin degradation product and D-dimer levels were significantly lower in the ROSC(+) group than in the ROSC(-) group (fibrin degradation products, 32.1 μg/mL versus 157.4 μg/mL; D-dimer, 9.9 μg/mL versus 37.4 μg/mL). The area under receiver operating characteristic curves to evaluate the relationship with return of spontaneous circulation of anion gap, albumin-corrected anion gap, fibrin degradation products, and D-dimer were 0.664, 0.667, 0.714, and 0.707, respectively.

Conclusion

Fibrin degradation products and D-dimer levels might be more useful as predictors of return of spontaneous circulation than anion gap and albumin-corrected anion gap.

Effect of the independent acid base variables on anion gap variation in cardiac surgical patients: a Stewart-Figge approach

PURPOSE

To determine the effect of each of independent acid base variables on the anion gap (AG) value in cardiac surgical patients.

METHODS

This retrospective study involved 128 cardiac surgical patients admitted for postoperative care. The variation of AG (AGvar) between the day of admission and the first postoperative day was correlated via a multiple linear regression model with the respective variations of the independent acid base variables, that is, apparent strong ion difference (SIDa), strong ion gap (SIG), carbon dioxide (PCO2), and albumin and phosphate concentrations.

RESULTS

The variations of all the above variables contributed significantly to the prediction of AGvar (adjusted R (2) = 0.9999, F = 201890.24, and P < 0.001). According to the standardized coefficients (β),  SIGvar (β = 0.948, P < 0.001), [Albumin]var (β = 0.260, P < 0.001), and [Phosphate]var (β = 0.191, P < 0.001) were the major determinants of AGvar with lesser contributions from SIDa, var (β = 0.071, P < 0.001) and PCO2, var (β = -0.067, P < 0.001).

CONCLUSIONS

All the independent acid base variables contribute to the prediction of the AG value. However, albumin and phosphate and SIG variations seem to be the most important predictors, while AG appears to be rather stable with changes in PCO2 and SIDa.

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 significance of albumin corrected anion gap in patients with cardiopulmonary arrest

PURPOSE

The reliable parameter, which can be obtained easily and quickly, is necessary to predict the return of spontaneous circulation (ROSC) of patients with cardiopulmonary arrest (CPA) in the emergency situation. In this study, we evaluated the significance of albumin corrected anion gap (ACAG) for the prediction of ROSC in patients with CPA.

PATIENTS AND METHODS

In 166 patients with CPA between January 2009 and December 2010, 132 patients could be analyzed retrospectively. We compared acute physiology and chronic health evaluation (APACHE) II score, sequential organ failure assessment(SOFA) score, anion gap (AG) and ACAG levels between patients with/without ROSC and evaluated the significance of AG and ACAG to predict ROSC in patients with CPA.

RESULTS

Both AG and ACAG were significantly lower in patients with ROSC than in patients without ROSC. Both AG and ACAG had the relation with APACHE II and SOFA scores, however, coefficients of correlation with APACHE II and SOFA score were higher in ACAG (r = 0.506) than in AG (r = 0.482). The sensitivity, specificity, positive predictive value, and negative predictive value of ACAG for the prediction of ROSC in patients with CPA were better than those of AG.

CONCLUSION

Our study shows that both AG and ACAG have the relation with ROSC and ACAG is better to predict the ROSC following CPR in patients with CPA compared with AG. ACAG can be easily obtained in the emergency situation, and ACAG is a useful parameter to predict ROSC in patients with CPA.

Anion gap, anion gap corrected for albumin, base deficit and unmeasured anions in critically ill patients: implications on the assessment of metabolic acidosis and the diagnosis of hyperlactatemia

Background

Base deficit (BD), anion gap (AG), and albumin corrected anion gap (ACAG) are used by clinicians to assess the presence or absence of hyperlactatemia (HL). We set out to determine if these tools can diagnose the presence of HL using cotemporaneous samples.

Methods

We conducted a chart review of ICU patients who had cotemporaneous arterial blood gas, serum chemistry, serum albumin (Alb) and lactate(Lac) levels measured from the same sample. We assessed the capacity of AG, BD, and ACAG to diagnose HL and severe hyperlactatemia (SHL). HL was defined as Lac > 2.5 mmol/L. SHL was defined as a Lac of > 4.0 mmol/L.

Results

From 143 patients we identified 497 series of lab values that met our study criteria. Mean age was 62.2 ± 15.7 years. Mean Lac was 2.11 ± 2.6 mmol/L, mean AG was 9.0 ± 5.1, mean ACAG was 14.1 ± 3.8, mean BD was 1.50 ± 5.4. The area under the curve for the ROC for BD, AG, and ACAG to diagnose HL were 0.79, 0.70, and 0.72, respectively.

Conclusion

AG and BD failed to reliably detect the presence of clinically significant hyperlactatemia. Under idealized conditions, ACAG has the capacity to rule out the presence of hyperlactatemia. Lac levels should be obtained routinely in all patients admitted to the ICU in whom the possibility of shock/hypoperfusion is being considered. If an AG assessment is required in the ICU, it must be corrected for albumin for there to be sufficient diagnostic utility.

Metabolic acid-base disorders in the critical care unit

The recognition and management of acid-base disorders is a commonplace activity in the critical care unit, and the role of weak and strong acids in the genesis of metabolic acid-base disorders is reviewed. The clinical approach to patients with metabolic alkalosis and metabolic acidosis is discussed in this article.

Anion gap, anion gap corrected for albumin, and base deficit fail to accurately diagnose clinically significant hyperlactatemia in critically ill patients

Anion gap, anion gap corrected for serum albumin, and base deficit are often used as surrogates for measuring serum lactate. None of these surrogates is postulated to predict hyperlactatemia in the critically ill. We prospectively collected data from September 2004 through August 2005 for 1381 consecutive admissions. Patients with renal disease, ketoacidosis, or toxic ingestion were excluded. Anion gap, anion gap corrected for albumin, and base deficit were calculated for all patients. We identified 286 patients who met our inclusion or exclusion criteria. The receiver-operating characteristic area under the curve for the prediction of hyperlactatemia for anion gap, anion gap corrected for albumin, and base deficit were 0.55, 0.57, and 0.64, respectively. Anion gap, anion gap corrected for albumin, and base deficit do not predict the presence or absence of clinically significant hyperlactatemia. Serum lactate should be measured in all critically ill adults in whom hypoperfusion is suspected.

Severe hyperlactatemia with normal base excess: a quantitative analysis using conventional and Stewart approaches

INTRODUCTION

Critically ill patients might present complex acid-base disorders, even when the pH, PCO2, [HCO3-], and base excess ([BE]) levels are normal. Our hypothesis was that the acidifying effect of severe hyperlactatemia is frequently masked by alkalinizing processes that normalize the [BE]. The goal of the present study was therefore to quantify these disorders using both Stewart and conventional approaches.

METHODS

A total of 1,592 consecutive patients were prospectively evaluated on intensive care unit admission. Patients with severe hyperlactatemia (lactate level > or = 4.0 mmol/l) were grouped according to low or normal [BE] values (<-3 mmol/l or >-3 mmol/l).

RESULTS

Severe hyperlactatemia was present in 168 of the patients (11%). One hundred and thirty-four (80%) patients had low [BE] levels while 34 (20%) patients did not. Shock was more frequently present in the low [BE] group (46% versus 24%, P = 0.02) and chronic obstructive pulmonary disease in the normal [BE] group (38% versus 4%, P < 0.0001). Levels of lactate were slightly higher in patients with low [BE] (6.4 +/- 2.4 mmol/l versus 5.6 +/- 2.1 mmol/l, P = 0.08). According to our study design, the pH, [HCO3-], and strong-ion difference values were lower in patients with low [BE]. Patients with normal [BE] had lower plasma [Cl-] (100 +/- 6 mmol/l versus 107 +/- 5 mmol/l, P < 0.0001) and higher differences between the changes in anion gap and [HCO3-] (5 +/- 6 mmol/l versus 1 +/- 4 mmol/l, P < 0.0001).

CONCLUSION

Critically ill patients may present severe hyperlactatemia with normal values of pH, [HCO3-], and [BE] as a result of associated hypochloremic alkalosis.

Comparison of three different methods of evaluation of metabolic acid-base disorders

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.

The lactate:pyruvate ratio following open cardiac surgery in children

OBJECTIVE

To explore the relationship between lactate:pyruvate ratio, hyperlactataemia, metabolic acidosis, and morbidity.

DESIGN AND SETTING

Prospective observational study in the paediatric intensive care unit (PICU) of a university hospital.

PATIENTS

Ninety-seven children after open cardiac surgery. Most children (94%) fell into low-moderate operative risk categories; observed PICU mortality was 1%.

INTERVENTIONS

Blood was sampled on admission for acid-base analysis, lactate, and pyruvate. Metabolic acidosis was defined as standard bicarbonate lower than 22 mmol/l, raised lactate as higher than 2 mmol/l, and raised lactate:pyruvate ratio as higher than 20.

MEASUREMENTS AND RESULTS

Median cardiopulmonary bypass and aortic cross-clamp times were 80 and 46 min. Metabolic acidosis occurred in 74%, hyperlactataemia in 42%, and raised lactate:pyruvate ratio in 45% of children. In multivariate analysis lactate:pyruvate ratio increased by 6.4 in children receiving epinephrine infusion and by 0.4 per 10 min of aortic cross-clamp. Duration of inotropic support increased by 0.29 days, ventilatory support by 0.27 days, and PICU stay by 0.42 days, for each 1 mmol/l increase in lactate. Neither standard bicarbonate nor lactate:pyruvate ratio were independently associated with prolongation of PICU support.

CONCLUSIONS

Elevated lactate:pyruvate ratio was common in children with mild metabolic acidosis and low PICU mortality. Hyperlactataemia, but not elevated lactate:pyruvate ratio or metabolic acidosis, was associated with prolongation of PICU support. Routine measurement of lactate:pyruvate ratio is not warranted for children in low-moderate operative risk categories.

Essentials of laboratory medicine for the nephrology clinician

The purpose of this review is to compile and bring to the attention of the pediatric nephrology community various aspects of laboratory medicine pertinent to nephrology. The review addresses different aspects in laboratory medicine that should be taken into account during interpretation of a test result, such as methodological and analytical issues, statistical considerations and the biological interpretation of a test result in the context of the clinical setting. An understanding of the considerations and limitations in laboratory medicine will be helpful to the pediatric nephrologist when ordering and interpreting biochemical tests.

The role of albumin in fluid and electrolyte balance

Albumin plays an important role in maintaining homeostasis within the body and depends on the cell membrane and the transport mechanism, including diffusion, osmosis, filtration, and active transport. The dissolved proteins, which are the only substances that do not penetrate the pores of the capillary membrane, are responsible for the osmotic pressure of the capillary membrane. Approximately 75% of the total colloid osmotic pressure is related to albumin.

Influence of hypoalbuminemia or hyperalbuminemia on the serum anion gap

BACKGROUND

Conflicting data exist as to what extent hypoalbuminemia reduces the anion gap; estimates range from 1.5 to 2.5 mM per g/dL decrease in serum albumin.

METHODS

We measured serum albumin, total protein, and electrolyte concentrations in 5328 consecutive patients aged 1 month to 102 years. Most patients (3750; 70%) had a normal albumin, but 1158 had hypoalbuminemia (< or =3.4 g/dL); 420 had hyperalbuminemia (> or =4.7 g/dL). Relationships between serum albumin or total protein and the anion gap were analyzed by linear regression.

RESULTS

309 (27%) hypoalbuminemic patients had a decreased anion gap, and 257 hyperalbuminemic patients (61%) had an increased anion gap. Among the entire group of 5328 patients, there were highly significant correlations between either serum albumin or total protein and the anion gap (P < 0.001). The slope of the regression for albumin versus anion gap was 2.3 mM per g/dL. Using this slope, anion gap could be adjusted for abnormal serum albumin levels: anion gap(adjusted) =anion gap + 2.3 (4-albumin). The initial assessment of an anion gap as being increased, normal, or decreased changed in 44% of the patients with hypo- or hyperalbuminemia once anion gap had been adjusted with this formula.

CONCLUSIONS

Before considering whether a disorder associated with an increased or decreased anion gap is present, the anion gap should be first adjusted for abnormal serum albumin concentrations. Our data suggest that physicians use 2.3 times the change in serum albumin, whereas those of Figge et al suggest 2.5; either approach gives similar results.

Clinical review: the meaning of acid-base abnormalities in the intensive care unit part I - epidemiology

Acid-base abnormalities are common in critically ill patients. Our ability to describe acid-base disorders must be precise. Small differences in corrections for anion gap, different types of analytical processes, and the basic approach used to diagnose acid-base aberrations can lead to markedly different interpretations and treatment strategies for the same disorder. By applying a quantitive acid-base approach, clinicians are able to account for small changes in ion distribution that may have gone unrecognized with traditional techniques of acid-base analysis. Outcome prediction based on the quantitative approach remains controversial. This is in part due to use of various technologies to measure acid-base variables, administration of fluid or medication that can alter acid-base results, and lack of standardized nomenclature. Without controlling for these factors it is difficult to appreciate the full effect that acid-base disorders have on patient outcomes, ultimately making results of outcome studies hard to compare.

Krebs cycle anions in metabolic acidosis

For many years it has been apparent from estimates of the anion gap and the strong ion gap that anions of unknown identity can be generated in sepsis and shock states. Evidence is emerging that at least some of these are intermediates of the citric acid cycle. The exact source of this disturbance remains unclear, because a great many metabolic blocks and bottlenecks can disturb the anaplerotic and cataplerotic pathways that enter and leave the cycle. These mechanisms require clarification with the use of tools such as gas chromatography–mass spectrometry.

Circulating anions usually associated with the Krebs cycle in patients with metabolic acidosis

Introduction

Acute metabolic acidosis of non-renal origin is usually a result of either lactic or ketoacidosis, both of which are associated with a high anion gap. There is increasing recognition, however, of a group of acidotic patients who have a large anion gap that is not explained by either keto- or lactic acidosis nor, in most cases, is inappropriate fluid resuscitation or ingestion of exogenous agents the cause.

Methods

Plasma ultrafiltrate from patients with diabetic ketoacidosis, lactic acidosis, acidosis of unknown cause, normal anion gap metabolic acidosis, or acidosis as a result of base loss were examined enzymatically for the presence of low molecular weight anions including citrate, isocitrate, α-ketoglutarate, succinate, malate and d-lactate. The results obtained from the study groups were compared with those obtained from control plasma from normal volunteers.

Results

In five patients with lactic acidosis, a significant increase in isocitrate (0.71 ± 0.35 mEq l^-1), α-ketoglutarate (0.55 ± 0.35 mEq l^-1), malate (0.59 ± 0.27 mEq l^-1), and d-lactate (0.40 ± 0.51 mEq l^-1) was observed. In 13 patients with diabetic ketoacidosis, significant increases in isocitrate (0.42 ± 0.35 mEq l^-1), α-ketoglutarate (0.41 ± 0.16 mEq l^-1), malate (0.23 ± 0.18 mEq l^-1) and d-lactate (0.16 ± 0.07 mEq l^-1) were seen. Neither citrate nor succinate levels were increased. Similar findings were also observed in a further five patients with high anion gap acidosis of unknown origin with increases in isocitrate (0.95 ± 0.88 mEq l^-1), α-ketoglutarate (0.65 ± 0.20 mEq l^-1), succinate (0.34 ± 0.13 mEq l^-1), malate (0.49 ± 0.19 mEq l^-1) and d-lactate (0.18 ± 0.14 mEq l^-1) being observed but not in citrate concentration. In five patients with a normal anion gap acidosis, no increases were observed except a modest rise in d-lactate (0.17 ± 0.14 mEq l^-1).

Conclusion

The levels of certain low molecular weight anions usually associated with intermediary metabolism were found to be significantly elevated in the plasma ultrafiltrate obtained from patients with metabolic acidosis. Our results suggest that these hitherto unmeasured anions may significantly contribute to the generation of the anion gap in patients with lactic acidosis and acidosis of unknown aetiology and may be underestimated in diabetic ketoacidosis. These anions are not significantly elevated in patients with normal anion gap acidosis.

Acid–base and electrolyte analysis in critically ill patients: are we ready for the new millennium?

PURPOSE OF REVIEW

Disorders of acid-base and electrolytes are commonly seen in critically ill patients. The presence of these disorders typically signals the development of an underlying pathology. These disturbances can be severe and are often associated with worse outcome. Indeed, metabolic acidosis is one of the ways we quantify organ failure. Although acid-base and electrolyte disorders may be a result of the underlying pathophysiology (eg, renal failure, respiratory failure, shock), they may also result from the way in which we manage critically ill patients.

RECENT FINDINGS

The application of the physical-chemical approach to acid-base analysis has led to recent developments in the identification and quantification and understanding of mechanisms for acid-base disorders commonly found in critically ill patients. Examples include a better understanding of the role of electrolytes (especially sodium and chloride) and weak acids in the pathophysiology of acid-base disorders, the implication of acid-base derangements on the inflammatory process and organ perfusion, and the importance of resuscitation fluid composition.

SUMMARY

By adopting a physical-chemical approach to acid-base analysis we are gaining insight to the complexities of acid-base disorders and how their treatments may affect outcome.