Higher serum bicarbonate levels within the normal range are associated with better survival and renal outcomes in African Americans

Urine Ammonium Concentrations and Cardiovascular and Kidney Outcomes in Systolic Blood Pressure Intervention Trial Participants with CKD

Key Points

Background

Impaired urine ammonium excretion is common in CKD and may identify risk of metabolic acidosis earlier than reductions in serum bicarbonate or pH and thus may have associations with cardiovascular disease (CVD) outcomes. We evaluated the association of urine ammonium with CVD and kidney outcomes among persons with hypertension and nondiabetic CKD enrolled in a trial of BP reduction.

Methods

We measured urine ammonium concentration in spot urine specimens collected at baseline among 2092 participants of the Systolic Blood Pressure Intervention Trial (SPRINT) with an eGFR <60 ml/min per 1.73 m2. We used multivariable-adjusted Cox models to evaluate associations of urine ammonium concentration with the SPRINT CVD composite outcome (myocardial infarction, acute coronary syndrome, stroke, heart failure, or CVD death), all-cause mortality, the SPRINT kidney composite outcome (50% kidney function decline, ESKD, or transplant), and AKI.

Results

At baseline, the mean (SD) age was 73 (9) years; 40% were female; and 25% were Black participants. The mean (SD) serum bicarbonate was 25.6 (2.8) mmol/L, median (interquartile range) urine ammonium concentration was 14.4 (9.5–23.1) mmol/L, and median (interquartile range) eGFR was 49 (39–55) ml/min per 1.73 m2. There were 255 CVD composite events, 143 deaths, 63 kidney composite events, and 146 AKI events during a median follow-up of 3.8 years. In multivariable models, each two-fold higher urinary ammonium concentration was associated with a 26% (95% confidence interval, 1.05 to 1.52) higher risk of the CVD composite, whereas there was no association with all-cause mortality, the SPRINT kidney composite outcome, or AKI.

Conclusions

Among nondiabetic individuals with hypertension and CKD, higher urine ammonium concentration is associated with higher risk of CVD. Further studies are needed to evaluate this association in other cohorts.

Metabolic Acidosis in CKD: Pathogenesis, Adverse Effects, and Treatment Effects

Metabolic acidosis is a frequent complication of chronic kidney disease and is associated with a number of adverse outcomes, including worsening kidney function, poor musculoskeletal health, cardiovascular events, and death. Mechanisms that prevent metabolic acidosis detrimentally promote further kidney damage, creating a cycle between acid accumulation and acid-mediated kidney injury. Disrupting this cycle through the provision of alkali, most commonly using sodium bicarbonate, is hypothesized to preserve kidney function while also mitigating adverse effects of excess acid on bone and muscle. However, results from clinical trials have been conflicting. There is also significant interest to determine whether sodium bicarbonate might improve patient outcomes for those who do not have overt metabolic acidosis. Such individuals are hypothesized to be experiencing acid-mediated organ damage despite having a normal serum bicarbonate concentration, a state often referred to as subclinical metabolic acidosis. Results from small- to medium-sized trials in individuals with subclinical metabolic acidosis have also been inconclusive. Well-powered clinical trials to determine the efficacy and safety of sodium bicarbonate are necessary to determine if this intervention improves patient outcomes.

A basic solution for a complex problem: does treatment of metabolic acidosis slow CKD progression?

PURPOSE OF THIS REVIEW

Metabolic acidosis is frequently encountered in patients with chronic kidney disease (CKD), with increasing prevalence as kidney function worsens. Treating electrolyte disturbances is the sine qua non of Nephrologists, and alkali therapy to normalize serum bicarbonate levels and slow progression of kidney disease has been embedded in clinical practice guidelines for decades on the basis of animal models and controversial clinical trials. This review will critically appraise the literature base for this recommendation and determine whether the available evidence supports this common practice, which is a timely endeavor considering the impending demotion of metabolic acidosis treatment from recommendation to practice point in forthcoming KDIGO guidelines.

RECENT FINDINGS

Earlier, open-label, studies supporting the utility of sodium bicarbonate therapy to slow progression of chronic kidney disease have been challenged by more recent, blinded, studies failing to show benefit on CKD progression. This was further demonstrated in the absence of concomitant sodium administration with the hydrochloric acid binder veverimer, which failed to demonstrate benefit on renal death, end stage kidney disease or 40% reduction in estimated glomerular filtration rate in a large multicenter trial.

SUMMARY

The current body of literature does not support the routine treatment of metabolic acidosis in patients with CKD and the authors agree with the forthcoming KDIGO guidelines to de-emphasize this common practice.

Pathophysiology of Diet-Induced Acid Stress

Diets can influence the body's acid-base status because specific food components yield acids, bases, or neither when metabolized. Animal-sourced foods yield acids and plant-sourced food, particularly fruits and vegetables, generally yield bases when metabolized. Modern diets proportionately contain more animal-sourced than plant-sourced foods, are, thereby, generally net acid-producing, and so constitute an ongoing acid challenge. Acid accumulation severe enough to reduce serum bicarbonate concentration, i.e., manifesting as chronic metabolic acidosis, the most extreme end of the continuum of "acid stress", harms bones and muscles and appears to enhance the progression of chronic kidney disease (CKD). Progressive acid accumulation that does not achieve the threshold amount necessary to cause chronic metabolic acidosis also appears to have deleterious effects. Specifically, identifiable acid retention without reduced serum bicarbonate concentration, which, in this review, we will call "covert acidosis", appears to cause kidney injury and exacerbate CKD progression. Furthermore, the chronic engagement of mechanisms to mitigate the ongoing acid challenge of modern diets also appears to threaten health, including kidney health. This review describes the full continuum of "acid stress" to which modern diets contribute and the mechanisms by which acid stress challenges health. Ongoing research will develop clinically useful tools to identify stages of acid stress earlier than metabolic acidosis and determine if dietary acid reduction lowers or eliminates the threats to health that these diets appear to cause.

Oral Sodium Bicarbonate and Bone Turnover in CKD: A Secondary Analysis of the BASE Pilot Trial

SIGNIFICANCE STATEMENT

In CKD, metabolic acidosis is commonly treated with alkali in the hope that it will improve bone health. In a post hoc analysis of the Bicarbonate Administration to Stabilize eGFR Pilot Trial, we investigated whether sodium bicarbonate affects serum levels of bone turnover markers and other hormones related to bone health in individuals with CKD who have normal to slightly reduced total CO2 (20-28 mEq/L). Sodium bicarbonate increased serum levels of α-klotho but had no significant effect on other bone health markers, including intact fibroblast growth factor-23 (iFGF-23), intact parathyroid hormone (iPTH), and bone-specific alkaline phosphatase (B-SAP). Further study is needed to determine the effect of bicarbonate administration on clinical aspects of bone health.

BACKGROUND

Treatment with alkali has been hypothesized to improve bone health in CKD by mitigating adverse effects of acid on bone mineral. We investigated the effect of treatment with sodium bicarbonate on bone turnover markers and other factors related to bone metabolism in CKD.

METHODS

This is a post hoc analysis of the Bicarbonate Administration to Stabilize eGFR Pilot Trial in which 194 individuals with CKD and serum total CO2 20-28 mEq/L were randomly assigned to placebo or one of two doses of sodium bicarbonate (0.5 or 0.8 mEq/kg lean body weight per day) for 28 weeks. The following serum measurements were performed at baseline, week 12, and week 28: B-SAP, c-telopeptide, procollagen type I intact N-terminal propeptide, iPTH, iFGF-23, soluble klotho, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and tartrate-resistant acid phosphatase 5b. The difference (sodium bicarbonate versus placebo) in mean change of each bone biomarker from baseline was determined using linear mixed models.

RESULTS

One hundred sixty-eight participants submitted samples for post hoc investigations. Mean eGFR was 37±10 ml/min per 1.73 m2 and mean total CO2 was 24±3 mEq/L at baseline. Sodium bicarbonate induced a dose-dependent increase in soluble klotho levels compared with placebo. There was no significant effect of treatment with either dose of sodium bicarbonate on any of the other bone biomarkers, including iFGF-23, iPTH, and B-SAP. Effects on bone biomarkers were similar in those with baseline serum total CO2 <24 mEq/L compared with those with total CO2 ≥24 mEq/L.

CONCLUSIONS

In this pilot trial of individuals with CKD and total CO2 20-28 mEq/L, sodium bicarbonate treatment increased serum klotho levels but did not affect other bone health markers over 28 weeks.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

ClinicalTrials.gov, NCT02521181.

Protein supplementation: the double-edged sword

Protein supplements are widely consumed by athletes as well as young adults and teenagers going to the gym and are an excellent source to increase protein intake, build muscle mass, and enhance recovery. They are available in the form of powders, gummies, protein bars, and ready-to-drink shakes and have been shown to have effects on almost every system in the body. Subjects consuming whey protein-based supplements regularly show significantly lower systolic blood pressure, while subjects who consume soy-based protein supplements have been reported to show a significant decrease in their systolic and diastolic blood pressures. Favorable effects of soy protein consumption have been observed on the serum lipid profile, with significant decreases in serum low-density lipoprotein and triglyceride levels. Lower postprandial glucose levels have been observed in diabetic subjects as well, which can be attributed to the lower glycemic index of these supplements. This can lead to an indirect decrease in diabetes-related complications. While these supplements affect the body positively, caution has to be exercised while consuming them in excess, as they have been shown to cause hyperfiltration and increased urinary calcium excretion which can, in turn, lead to chronic kidney disease development. This article focuses on the effects of protein supplementation on the human body, with emphasis on the cardiovascular, endocrine, and renal systems.

Venous bicarbonate and CKD progression: a longitudinal analysis by the group-based trajectory model

Background

Metabolic acidosis accelerates chronic kidney disease (CKD) progression towards kidney failure in animal models. Clinical trials testing the effect of bicarbonate on kidney outcomes are underpowered and/or of suboptimal quality. On the other hand, observational studies testing the same hypothesis are generally based on bicarbonate measured at a single time point.

Methods

We studied the longitudinal relationship between repeated venous bicarbonate levels and a predefined composite renal outcome (a ≥30% estimated glomerular filtration rate reduction, dialysis or transplantation) by using group-based trajectory model (GBTM) analysis. The GBTM analysis was used to classify patients based on individual bicarbonate levels over time. The relationship between trajectory groups and renal outcomes was investigated using crude and adjusted Cox regression models. A total of 528 patients with stage 2-5 CKD were included in the analysis.

Results

The GBTM analysis identified four distinct trajectories of bicarbonate levels: low, moderate, moderate-high and high. During the follow-up period, 126 patients experienced the combined renal endpoint. The hazard rate of renal events decreased dose-dependently from the lowest to the highest bicarbonate trajectory. After adjusting for potential confounders, there was a 63% risk reduction for the composite renal endpoint for patients in the high trajectory category compared with those in the low trajectory category.

Conclusion

The study found that higher bicarbonate trajectories were associated with a lower risk of adverse renal outcomes in CKD patients. These results suggest that strategies to maintain higher bicarbonate levels may benefit patients with CKD. However, further high-quality randomised trials are needed to confirm these findings and recommend bicarbonate supplementation as a strategy to delay CKD progression.

The effects of oral sodium bicarbonate supplementation on anthropometric measures in patients with chronic kidney disease: A systematic review and meta-analysis of randomized clinical trials

Metabolic acidosis (MA) may play a key role in the pathogenesis of protein-energy wasting (PEW) in patients with chronic kidney disease (CKD). To present a comprehensive synthesis of the effect of oral sodium bicarbonate (SB) supplementation on anthropometric measures in patients with CKD, a systematic review was undertaken in PubMed/MEDLINE, Web of Science, Cochrane CENTRAL, and Google Scholar, of relevant articles published prior to September 2022. The summary statistics of effect size, nonstandardized weighted mean difference (WMD), and 95% confidence interval (CI) were used to compare the effects of SB supplementation on anthropometric parameters vs. control group. To detect probable sources of heterogeneity, a series of predefined subgroup analyses were conducted. In total, 17 studies with 21 treatment arms, including 2203 participants (1149 cases, 1054 controls), met our inclusion criteria and were included in the meta-analysis. SB supplementation had no significant effect on body weight (BW), midarm muscle circumference (MAMC), or lean body mass (LBM) in patients with CKD. There was a significant increase in body mass index (BMI) (MD: 0.59 kg/m2, 95% CI: 0.25 to 0.93, p = 0.001) after SB supplementation in the overall analysis. In subgroup analysis, LBM was increased in studies that were ≥ 24-week duration (MD: 1.81 kg, 95% CI: 0.81 to 2.81) and in participants with BMI lower than 27 kg/m2 (MD: 1.81 mg/L, 95% CI: 0.81 to 2.81). SB supplementation may yield increases in BMI in predialysis CKD patients. However, our findings did not support the beneficial effects of SB supplementation on other anthropometric outcomes. There is an evident need for long-term high-quality interventions to confirm these findings.

Impact of decreased levels of total CO2 on in-hospital mortality in patients with COVID-19

Decreased total CO2 (tCO2) is significantly associated with all-cause mortality in critically ill patients. Because of a lack of data to evaluate the impact of tCO2 in patients with COVID-19, we assessed the impact of tCO2 on all-cause mortality in this study. We retrospectively reviewed the data of hospitalized patients with COVID-19 in two Korean referral hospitals between February 2020 and September 2021. The primary outcome was in-hospital mortality. We assessed the impact of tCO2 as a continuous variable on mortality using the Cox-proportional hazard model. In addition, we evaluated the relative factors associated with tCO2 ≤ 22 mmol/L using logistic regression analysis. In 4,423 patients included, the mean tCO2 was 24.8 ± 3.0 mmol/L, and 17.9% of patients with tCO2 ≤ 22 mmol/L. An increase in mmol/L of tCO2 decreased the risk of all-cause mortality by 4.8% after adjustment for age, sex, comorbidities, and laboratory values. Based on 22 mmol/L of tCO2, the risk of mortality was 1.7 times higher than that in patients with lower tCO2. This result was maintained in the analysis using a cutoff value of tCO2 24 mmol/L. Higher white blood cell count; lower hemoglobin, serum calcium, and eGFR; and higher uric acid, and aspartate aminotransferase were significantly associated with a tCO2 value ≤ 22 mmol/L. Decreased tCO2 significantly increased the risk of all-cause mortality in patients with COVID-19. Monitoring of tCO2 could be a good indicator to predict prognosis and it needs to be appropriately managed in patients with specific conditions.

Sodium Bicarbonate Treatment and Vascular Function in CKD: A Randomized, Double-Blind, Placebo-Controlled Trial

SIGNIFICANCE STATEMENT

Lower serum bicarbonate levels, even within the normal range, are strongly linked to risks of cardiovascular disease in CKD, possibly by modifying vascular function. In this randomized, controlled trial, treatment with sodium bicarbonate (NaHCO 3 ) did not improve vascular endothelial function or reduce arterial stiffness in participants with CKD stage 3b-4 with normal serum bicarbonate levels. In addition, NaHCO 3 treatment did not reduce left ventricular mass index. NaHCO 3 did increase plasma bicarbonate levels and urinary citrate excretion and reduce urinary ammonium excretion, indicating that the intervention was indeed effective. NaHCO 3 therapy was safe with no significant changes in BP, weight, or edema. These results do not support the use of NaHCO 3 for vascular dysfunction in participants with CKD.

BACKGROUND

Lower serum bicarbonate levels, even within the normal range, are strongly linked to risks of cardiovascular disease in CKD, possibly by modifying vascular function. Prospective interventional trials with sodium bicarbonate (NaHCO 3 ) are lacking.

METHODS

We conducted a randomized, double-blind, placebo-controlled trial examining the effect of NaHCO 3 on vascular function in 109 patients with CKD stage 3b-4 (eGFR 15-44 ml/min per 1.73 m 2 ) with normal serum bicarbonate levels (22-27 mEq/L). Participants were randomized 1:1 to NaHCO 3 or placebo at a dose of 0.5 mEq/lean body weight-kg per day for 12 months. The coprimary end points were change in brachial artery flow-mediated dilation (FMD) and change in aortic pulse wave velocity over 12 months.

RESULTS

Ninety patients completed this study. After 12 months, plasma bicarbonate levels increased significantly in the NaHCO 3 group compared with placebo (mean [SD] difference between groups 1.35±2.1, P = 0.003). NaHCO 3 treatment did not result in a significant improvement in aortic pulse wave velocity from baseline. NaHCO 3 did result in a significant increase in flow-mediated dilation after 1 month; however, this effect disappeared at 6 and 12 months. NaHCO 3 resulted in a significant increase in 24-hour urine citrate and pH and a significant decrease in 24-hour urine ammonia. There was no significant change in left ventricular mass index, ejection fraction, or eGFR with NaHCO 3 . NaHCO 3 treatment was safe and well-tolerated with no significant changes in BP, antihypertensive medication, weight, plasma calcium, or potassium levels.

CONCLUSION

Our results do not support the use of NaHCO 3 for vascular dysfunction in participants with CKD and normal serum bicarbonate levels.

Markers of Kidney Tubule Dysfunction and Major Adverse Kidney Events

BACKGROUND

Serum creatinine and albuminuria are primary markers of glomerular function and injury, respectively. Tubular secretion, acid-base homeostasis, protein reabsorption, among other tubular functions, are largely ignored. This mini-review aimed to discuss how two tubular functions, secretion, and acid-base homeostasis are associated with major adverse kidney events (MAKEs).

SUMMARY

Proximal tubular secretion is an essential function that allows the elimination of endogenous substances and drugs. Recently discovered endogenous markers in urine and plasma allow a noninvasive way of assessing tubular secretion markers. Several studies have found an association between these markers and a higher risk of chronic kidney disease (CKD) progression and mortality. In a study we recently performed among patients with CKD and at risk of cardiovascular events, lower tubular secretion was associated with an increased risk of acute kidney injury and metabolic acidosis, independent of baseline eGFR and albuminuria. The kidney tubules also play a crucial role in acid-base homeostasis. Although the standard clinical assessment of acidosis consists of measuring serum bicarbonate, urinary ammonium excretion decreases before over metabolic acidosis. Urinary ammonium excretion is associated with CKD progression, a higher risk of kidney failure, and an increased mortality risk, independent of baseline eGFR and albuminuria.

KEY MESSAGES

Novel biomarkers of kidney tubular health consistently associate with MAKEs, above and beyond baseline eGFR, albuminuria, and other CKD risk factors. Tubular markers may provide new opportunities to improve kidney prognosis, drug dosing, and monitoring for adverse events.

Hidden Acid Retention with Normal Serum Bicarbonate Level in Chronic Kidney Disease

Management of metabolic acidosis is crucial for preserving bone, muscle, and renal health, as evidenced by the results of several interventional studies conducted on patients with chronic kidney disease (CKD). Considering the continuity of CKD progression over time, it is reasonable to deduce that a subclinical form of metabolic acidosis may exist prior to the manifestation of overt metabolic acidosis. Covert H⁺ retention with normal serum bicarbonate level in patients with CKD may result in maladaptive responses that contribute to kidney function deterioration, even in the early stages of the disease. The loss of adaptive compensatory mechanisms of urinary acid excretion may be a key factor in this process. Early modulation of these responses could be an important therapeutic strategy in preventing CKD progression. However, to date, the optimal approach for alkali therapy in subclinical metabolic acidosis in CKD remains uncertain. There is a lack of established guidelines on when to initiate alkali therapy, potential side effects of alkali agents, and the optimal blood bicarbonate levels based on evidence-based practices. Therefore, further research is necessary to address these concerns and establish more robust guidelines for the use of alkali therapy in patients with CKD. Herein, we provide an overview of recent developments on this subject and examine the potential therapeutic approaches that interventional treatments may present for patients with hidden H⁺ retention, exhibiting normal serum bicarbonate levels - commonly described as subclinical or eubicarbonatemic metabolic acidosis in patients with CKD.

Treatment costs for patients with Streptococcus suis infection in Northern Thailand: a hospital-based observational study of 14-year data

BACKGROUND

Streptococcus suis (S.suis) is a neglected zoonotic disease that imposes a significant economic burden on healthcare and society. To our knowledge, studies estimating the cost of illness associated with S.suis treatment are limited, and no study focuses on treatment costs and potential key drivers in Thailand. This study aimed to estimate the direct medical costs associated with S.suis treatment in Thailand and identify key drivers affecting high treatment costs from the provider's perspective.

METHODS

A retrospective analysis of the 14-year data from 2005-2018 of confirmed S.suis patients admitted at Chiang Mai University Hospital (CMUH) was conducted. Descriptive statistics were used to summarize the data of patients' characteristics, healthcare utilization and costs. The multiple imputation with predictive mean matching strategy was employed to deal with missing Glasgow Coma Scale (GCS) data. Generalized linear models (GLMs) were used to forecast costs model and identify determinants of costs associated with S.suis treatment. The modified Park test was adopted to determine the appropriate family. All costs were inflated applying the consumer price index for medical care and presented to the year 2019.

RESULTS

Among 130 S.suis patients, the average total direct medical cost was 12,4675 Thai baht (THB) (US$ 4,016), of which the majority of expenses were from the "others" category (room charges, staff services and medical devices). Infective endocarditis (IE), GCS, length of stay, and bicarbonate level were significant predictors associated with high total treatment costs. Overall, marginal increases in IE and length of stay were significantly associated with increases in the total costs (standard error) by 132,443 THB (39,638 THB) and 5,490 THB (1,715 THB), respectively. In contrast, increases in GCS and bicarbonate levels were associated with decreases in the total costs (standard error) by 13,118 THB (5,026 THB) and 7,497 THB (3,430 THB), respectively.

CONCLUSIONS

IE, GCS, length of stay, and bicarbonate level were significant cost drivers associated with direct medical costs. Patients' clinical status during admission significantly impacts the outcomes and total treatment costs. Early diagnosis and timely treatment were paramount to alleviate long-term complications and high healthcare expenditures.

Glycoproteomics meets thermodynamics: A calorimetric study of the effect of sialylation and synergistic anion on the binding of iron to human serum transferrin

The thermodynamic parameters for the binding of ferric ions to human serum transferrin (hTf) as the major mediator of iron transport in blood plasma were determined by isothermal titration calorimetry in the presence of carbonate and oxalate as synergistic anions at pH 7.4. The results indicate that the binding of ferric ions to the two binding sites of hTf is driven both enthalpically and entropically in a lobe-dependent manner: binding to the C-site is mainly enthalpically driven, whereas binding to the N-site is mainly entropically driven. Lower sialic acid content of hTf leads to more exothermic apparent binding enthalpies for both lobes, while the increased apparent binding constants for both sites were found in the presence of carbonate. Sialylation also unequally affected the heat change rates for both sites only in the presence of carbonate, but not in the presence of oxalate. Overall, the results suggest that the desialylated hTf has a higher iron sequestering ability, which may have implications for iron metabolism.

Effects of topiramate therapy on serum bicarbonate concentration in a sample of 10,279 veterans

BACKGROUND

Topiramate, which is increasingly being used to treat alcohol use disorder (AUD), is commonly associated with reduced serum bicarbonate concentrations. However, estimates of the prevalence and magnitude of this effect are from small samples and do not address whether topiramate's effects on acid-base balance differ in the presence of an AUD or by topiramate dosage.

METHODS

Veterans Health Administration electronic health record (EHR) data were used to identify patients with a minimum of 180 days of topiramate prescription for any indication and a propensity score-matched control group. We differentiated patients into two subgroups based on the presence of a diagnosis of AUD in the EHR. Baseline alcohol consumption was determined using Alcohol Use Disorders Identification Test-Consumption (AUDIT-C) scores in the EHR. Analysis also included a three-level measure representing mean daily dosage. The topiramate-associated changes in serum bicarbonate concentration were estimated in difference-in-differences linear regression models. A serum bicarbonate concentration <17 mEq/L was considered to represent possible clinically significant metabolic acidosis.

RESULTS

The cohort comprised 4287 topiramate-treated patients and 5992 propensity score-matched controls with a mean follow-up period of 417 days. The mean topiramate-associated reductions in serum bicarbonate concentration were <2 mEq/L in the low (≤88.75), medium (>88.75 and ≤141.70), and high (>141.70) mg/day dosage tertiles, irrespective of AUD history. Concentrations <17 mEq/L occurred in 1.1% of topiramate-treated patients and 0.3% of controls and were not associated with alcohol consumption or an AUD diagnosis.

CONCLUSIONS

The excess prevalence of metabolic acidosis associated with topiramate treatment does not differ with dosage, alcohol consumption, or the presence of an AUD. Baseline and periodic serum bicarbonate concentration measurements are recommended during topiramate therapy. Patients prescribed topiramate should be educated about the symptoms of metabolic acidosis and urged to report their occurrence promptly to a healthcare provider.

Associations of the Serum Total Carbon Dioxide Level with Long-Term Clinical Outcomes in Sepsis Survivors

INTRODUCTION

Sepsis is characterized by a dysregulated host response to infection that leads to multiple organ dysfunction and often complicated with metabolic acidosis. However, the associations between serum total carbon dioxide level (TCO₂) and long-term clinical outcomes in sepsis survivors remains unknown.

METHODS

A total of 7212 sepsis survivors aged ≥ 20 years who were discharged from January  1, 2008 to December 31, 2018 were included in our analyses. The sepsis survivors were further divided into high TCO₂ (≥ 18 mmol/L) and low TCO₂ (< 18 mmol/L) groups, comprising 5023 and 2189 patients, respectively. The following outcomes of interest were included: all-cause mortality, myocardial infarction, ischemic stroke, hospitalization for heart failure, ventricular arrhythmia, and end-stage renal disease (ESRD).

RESULTS

After propensity score matching, the low TCO₂ group was at higher risks of all-cause mortality (hazard ratio [HR] 1.28, 95% confidence interval [95% CI] 1.18-1.39), myocardial infarction (HR 1.83, 95% CI 1.39-2.43), and ESRD (HR 1.38, 95% CI 1.16-1.64) than the high TCO₂ group. The results remained similar after considering death as a competing risk.

CONCLUSION

Patients discharged from hospitalization for sepsis have higher risks of worse long-term clinical outcomes. Physicians may need to pay more attention to sepsis survivors whose TCO₂ was low.

Predictive value of admission CO2 combining power combined with serum sodium for the prognosis in acute Stanford type A aortic dissection patients

Acute Stanford type A aortic dissection (ATAAD) with sudden onset and high mortality requiries a standard Bentall operation and a accurate prognosis in common, together with alteration of CO₂ combining power (CO₂CP) and serum sodium rase concern, hence, we evaluated the prognostic value of CO₂CP combined with serum sodium in ATAAD patients. This retrospective study included 183 patients who underwent Bentall operation for ATAAD from 2015 to 2021 in the Fourth Hospital of Hebei Medical University, subsequently followed grouping by the levels of CO₂CP and serum sodium. The study endpoint was 30-day all-cause mortality, and the prognostic value of CO₂CP combined with serum sodium levels in ATAAD patients were evaluated with multivariate logistic regression method. The postoperative incidence of in-hospital death and adverse events in patients with ATAAD were 18% and 25.7%, respectively. Combination of CO₂CP and serum sodium for predicting ATAAD death and adverse events presented a higher predictive value than each single indicator with ROC curve analysis (the AUC of CO₂CP combined with serum sodium was 0.786, 95% CI 0.706-0.869, P < 0.001), along with CO₂CP < 22.5 mmol/L + serum sodium > 138.5 mmol/L group had the worst prognostic. Multivariate regression analyse showed that CO₂CP < 22.5 mmol/L combined with serum sodium > 138.5 mmol/L preferably predicted the prognosis of ATAAD (OR =6.073, 95% CI 2.557-14.425, P < 0.001). Consistently, the cumulative 30-day survival after surgery in ATAAD patients with the low CO₂CP and high serum sodium simultaneously was the worst (log-rank P < 0.05). The combination of CO₂CP and serum sodium increases the predictive value of prognosis, which is conducive to risk stratification of patients with ATAAD.

Longitudinal trajectory of acidosis and mortality in acute kidney injury requiring continuous renal replacement therapy

BACKGROUND

Acidosis frequently occurs in severe acute kidney injury (AKI), and continuous renal replacement therapy (CRRT) can control this pathologic condition. Nevertheless, acidosis may be aggravated; thus, monitoring is essential after starting CRRT. Herein, we addressed the longitudinal trajectory of acidosis on CRRT and its relationship with worse outcomes.

METHODS

The latent growth mixture model was applied to classify the trajectories of pH during the first 24 hours and those of C-reactive protein (CRP) after 24 hours on CRRT due to AKI (n = 1815). Cox proportional hazard models were used to calculate hazard ratios of all-cause mortality after adjusting multiple variables or matching their propensity scores.

RESULTS

The patients could be classified into 5 clusters, including the normally maintained groups (1st cluster, pH = 7.4; and 2nd cluster, pH = 7.3), recovering group (3rd cluster with pH values from 7.2 to 7.3), aggravating group (4th cluster with pH values from 7.3 to 7.2), and ill-being group (5th cluster, pH < 7.2). The pH clusters had different trends of C-reactive protein (CRP) after 24 hours; the 1st and 2nd pH clusters had lower levels, but the 3rd to 5th pH clusters had an increasing trend of CRP. The 1st pH cluster had the best survival rates, and the 3rd to 5th pH clusters had the worst survival rates. This survival difference was significant despite adjusting for other variables or matching propensity scores.

CONCLUSIONS

Initial trajectories of acidosis determine subsequent worse outcomes, such as mortality and inflammation, in patients undergoing CRRT due to AKI.

Chronic Sub-Clinical Systemic Metabolic Acidosis - A Review with Implications for Clinical Practice

When arterial serum pH remains near the lower pH limit of 7.35 for protracted periods of time, a low-grade, sub-clinical form of acidosis results, referred to in this review as chronic, sub-clinical, systemic metabolic acidosis (CSSMA). This narrative review explores the scientific basis for CSSMA, its consequences for health, and potential therapeutic interventions. The major etiology of CSSMA is the shift away from the ancestral, alkaline diet which was rich in fruit and vegetables, toward the contemporary, acidogenic 'Westernized' diet characterized by higher animal protein consumption and lack of base forming minerals. Urine pH is reduced with high dietary acid load and may be a convenient marker of CSSMA. Evidence suggests further that CSSMA negatively influences cortisol levels potentially contributing significantly to the pathophysiology thereof. Both CSSMA and high dietary acid load are associated with the risk and prognosis of various chronic diseases. Clinical trials show that CSSMA can be addressed successfully through alkalizing the diet by increasing fruit and vegetable intake and/or supplementing with alkaline minerals. This review confirms the existence of a significant body of evidence regarding this low-grade form of acidosis as well as evidence to support its diverse negative implications for health, and concludes that CSSMA is a condition warranting further research.

Associations of Metabolic Syndrome and Abdominal Obesity with Anion Gap Metabolic Acidosis among US Adults

BACKGROUND

Obesity is a recently identified risk factor for metabolic acidosis and anion gap elevations in the absence of CKD. Metabolic acidosis is a treatable condition with substantial adverse effects on human health. Additional investigations are needed to characterize at-risk populations and explore potential mechanisms. We hypothesized metabolic syndrome (MetS) and waist circumference (WC) would be closely associated with this pathology.

METHODS

Adult participants from NHANES 1999-2018 meeting study criteria were compiled as main (n=31,163) and fasting (n=12,860) cohorts. Regression models adjusted for dietary acid, eGFR, and other factors examined associations of WC and MetS features with anion gap metabolic acidosis and its components (serum bicarbonate ≤23 mEq/L and anion gap >95th percentile).

RESULTS

Greater WC and MetS features were associated with progressively lower bicarbonate, higher anion gap, and greater odds ratios (OR) of metabolic acidosis (MA) and anion gap metabolic acidosis (AGMA). Compared with the reference, participants with the highest WC had ORs for MA and AGMA of 2.26; 95% CI, 1.96 to 2.62 and 2.89; 95% CI, 1.97 to 4.21; those with three and four versus zero MetS features had ORs for AGMA of 2.52; 95% CI, 1.95 to 2.94 and 3.05; 95% CI, 2.16 to 3.82. Associations of body mass index with outcomes were attenuated or absent after adjustment for WC or MetS. Findings were preserved after excluding eGFR <90 ml/min per 1.73 m² and albuminuria. A lower MA cutoff (<22 mEq/L) raised the estimate of association between MetS and MA (OR for three and four vs zero features: 3.56; 95% CI, 2.53 to 5.02 and 5.44; 95% CI, 3.66 to 8.08).

CONCLUSIONS

Metabolic diseases are characterized by metabolic acidosis and anion gap elevations. Metabolic dysfunction may predispose patients without CKD to systemic acidosis from endogenous sources. Comprehensive acid-base analyses may be informative in patients with metabolic diseases.

Low Serum Bicarbonate Levels Increase the Risk of All-Cause, Cardiovascular Disease, and Cancer Mortality in Type 2 Diabetes

CONTEXT

The evidence regarding bicarbonate status and mortality among diabetes is scarce.

OBJECTIVE

The purpose of this study was to investigate the associations of bicarbonate concentrations with risk of all-cause, cardiovascular disease (CVD), and cancer mortality among patients with type 2 diabetes (T2D).

METHODS

This study included 8163 adult diabetic patients from the National Health and Nutrition Examination Survey (NHANES), 1999 to 2018. Death outcomes were ascertained by linkage to National Death Index records through 31 December 2019. The Cox proportional-risk model was used to estimate hazard ratios (HR) and 95% CIs for mortality from all causes, CVD, and cancer. The mediating effects of 11 metabolic, cardiovascular, and renal biomarkers were evaluated using a logistic regression model within a counterfactual framework.

RESULTS

During 8163 person-years of follow-up, 2310 deaths were documented, including 659 CVD deaths and 399 cancer deaths. After multivariate adjustment, lower serum bicarbonate levels were significantly linearly correlated with higher all-cause, CVD, and cancer mortality: The risk of all-cause death increased by 40%, the risk of CVD death increased by 48%, and the risk of cancer death increased by 84% compared with the normal group (all P < .05). Altered levels of estimated glomerular filtration rate explained 12.10% and 16.94% of the relation between serum bicarbonate with all-cause and CVD mortality, respectively. Total cholesterol mediated 4.70% and 10.51% of the associations of all-cause and CVD mortality, respectively.

CONCLUSION

Lower serum bicarbonate concentrations were significantly associated with higher all-cause, CVD, and cancer mortality. These findings suggest that maintaining adequate bicarbonate status may lower mortality risk in individuals with T2D.

Metabolic acidosis post kidney transplantation

Metabolic acidosis, a common complication in patients with chronic kidney disease (CKD), results in a multitude of deleterious effects. Though the restoration of kidney function following transplantation is generally accompanied by a correction of metabolic acidosis, a subset of transplant recipients remains afflicted by this ailment and its subsequent morbidities. The vulnerability of kidney allografts to metabolic acidosis can be attributed to reasons similar to pathogenesis of acidosis in non-transplant CKD, and to transplant specific causes, including donor related, recipient related, immune mediated factors, and immunosuppressive medications. Correction of metabolic acidosis in kidney transplantation either with alkali therapy or through dietary manipulations may have potential benefits and the results of such clinical trials are eagerly awaited. This review summarizes the published evidence on the pathogenesis and clinical consequences of chronic metabolic acidosis in kidney transplant recipients.

The Importance of Recognizing and Addressing the Spectrum of Acid Stress

Acid accumulation sufficient to reduce plasma bicarbonate concentration, thereby recognized as chronic metabolic acidosis, harms bones and muscles and appears to enhance progression of CKD. Evolving evidence supports that progressive acid accumulation that is not enough to cause chronic metabolic acidosis nevertheless has deleterious effects. Measurable acid retention without reduced plasma bicarbonate concentration, called eubicarbonatemic acidosis, also appears to cause kidney injury and exacerbate CKD progression. Furthermore, chronic engagement of mechanisms to mitigate the ongoing acid challenge of net acid-producing diets of developed societies also appears to be deleterious, including for kidney health. This review challenges clinicians to consider the growing evidence for a spectrum of acid-accumulation disorders that include lesser degrees of acid accumulation than metabolic acidosis yet are harmful. Further research will develop clinically useful tools to identify individuals suffering from these earlier stages of acid stress and determine if the straightforward and comparatively inexpensive intervention of dietary acid reduction relieves or eliminates the harm they appear to cause.

Management of Metabolic Acidosis in Chronic Kidney Disease: Past, Present, and Future Direction

Chronic kidney disease (CKD) is a major global epidemic associated with increased morbidity and mortality. Despite the effectiveness of kidney protection strategies of hypertension, diabetes, and lipid control and use of newer hypoglycemic agents and anti-angiotensin II drugs, the nephropathy in CKD continues unabated toward irreversible kidney failure. Thus, interventions targeting modifiable risk factors in CKD such as metabolic acidosis (MA) are needed. Acid reduction with sodium-based alkali has been shown to be an effective kidney-protection strategy for patients with CKD and reduced glomerular filtration rate (GFR). Small-scale studies reveal diets emphasizing ingestion of plant-sourced over animal-sourced protein reduce dietary acid, improve MA, and slow further nephropathy progression in patients with CKD and reduced GFR. Additionally, veverimer, an investigational, nonabsorbed polymer that binds and removes gastrointestinal hydrochloric acid, is being developed as a novel treatment for MA. As further studies define how to best use these interventions for kidney protection, clinicians must become aware of their potential utility in the management of patients with CKD. The aim of the present review is to explore the various intervention strategies that increase or normalize serum [HCO₃^-] in patients with CKD-associated MA or low normal serum [HCO₃^-] that may further slow progression of CKD.

Importance of Metabolic Acidosis as a Health Risk in Chronic Kidney Disease

Human kidneys are well adapted to excrete the daily acid load from diet and metabolism in order to maintain homeostasis. In approximately 30% of patients with more advanced stages of CKD, these homeostatic processes are no longer adequate, resulting in metabolic acidosis. Potential deleterious effects of chronic metabolic acidosis in CKD, including muscle wasting, bone demineralization, hyperkalemia, and more rapid progression of CKD, have been well cataloged. Based primarily upon concerns related to nutrition and bone disease, early Kidney Disease Outcomes Quality Initiative guidelines recommended treating metabolic acidosis with alkali therapy targeting a serum bicarbonate ≥22 mEq/L. More recent guidelines have suggested similar targets based upon potential slowing of CKD progression. However, appropriately powered, long-term, randomized controlled trials to study efficacy and safety of alkali therapy for these outcomes are largely lacking. As a result, practice among physicians varies, underscoring the complexity of treatment of chronic metabolic acidosis in real-world CKD practice. Novel treatment approaches and rigorous phase 3 trials may resolve some of this controversy in the coming years. Metabolic acidosis is an important complication of CKD, and where it "falls" in the priority schema of CKD care will depend upon the generation of strong clinical evidence.

Elevated Serum Chloride Levels Contribute to a Poor Prognosis in Patients with IgA Nephropathy

Introduction

The identification of reliable prognostic factors is a crucial requirement for patients with IgA nephropathy (IgAN). Here, we explored the relationship between serum chloride levels and prognosis in patients with IgAN.

Methods

We recruited all patients with primary IgAN, as diagnosed by renal biopsy, between 1^st January 2015 and 1^st April 2019. Patients were divided two groups (high chloride group and low chloride group) based on the best cut-off values from survival receiver operating characteristic (ROC) curves. The baseline clinicopathological characteristics of two groups were then compared. Cox proportional hazard models were used to determine the prognostic value of serum chloride levels in patients with IgAN. Finally, we screened reliable prognostic indicators and built a clinical prediction model and validated the performance of the model.

Results

Compared with patients in the high chloride group, patients in the low chloride group had significantly lower levels of 24-hour urinary total protein (24 h-UTP), serum creatinine (sCr), and higher levels of hemoglobin (Hb), albumin (all p < 0.05), and less proportion of Oxford classification grade E1 (endothelial cell proliferation) and T2 (renal tubule atrophy or renal interstitial fibrosis). Cox analysis revealed that serum chloride level ≥ 105.4 mmol/L was a significant and independent risk factor for prognosis in patients with IgAN (p < 0.05). Serum chloride, sCr, T, hypertension, and Hb were used to generate a predictive model for prognosis. Thec-indices of our predictive model were 0.80, 0.86, and 0.78, for 1, 2, and 3 years, respectively; Brier scores were 0.06, 0.09, and 0.16, respectively.

Conclusions

A serum chloride level ≥ 105.4 mmol/l was identified as a significant and independent risk factor for the prognosis of patients with IgAN. A predictive prognosis model was generated using serum chloride, sCr, T, hypertension, and Hb; this model exhibited a good predictive effect.

Lower bicarbonate level is associated with CKD progression and all-cause mortality: a propensity score matching analysis

Background

Although metabolic acidosis is known as a potential complication of chronic kidney disease (CKD), there is limited information concerning the association between metabolic acidosis and clinical outcomes.

Methods

Five hundred fifty-two patients referred to renal division of Iwata City Hospital from 2015 to 2017 were included as a retrospective CKD cohort, and finally 178 patients with CKD stage III or IV and 20 to 80 years of age were analyzed. We examined the association between serum bicarbonate (HCO₃⁻) levels and clinical outcomes using Kaplan-Meier methods after the matching of baseline characteristics by propensity scores.

Results

Of 178 patients with CKD, patients with lower HCO₃⁻ levels (N = 94), as compared with patients with higher HCO₃⁻ levels (N = 84), were more likely to be male (P < 0.05), had more severe CKD stages (P < 0.05), more frequent use of renin-angiotensin system inhibitor (P < 0.05) or uric acid lowering agent (P < 0.001), heavier body weight (P < 0.001) and lower estimated glomerular filtration rate (P < 0.05). In Kaplan-Meier analysis after propensity score matching, the incidence of composite outcome as the doubling of serum creatinine level from baseline, end-stage kidney disease requiring the initiation of dialysis, or death from any causes was significantly fewer in the higher HCO₃⁻ group than the lower HCO₃⁻ group (N = 57 each group, P = 0.016).

Conclusions

Lower HCO₃⁻ level is significantly associated with the doubling of serum creatinine level, end-stage kidney disease or all-cause mortality in patients with CKD.

Trial registration

This study was registered with the Clinical Trial Registry of the University Hospital Medical Information Network (http://www.umin.ac.jp/, study number: UMIN000044861).

Effects of oral alkali drug therapy on clinical outcomes in pre-dialysis chronic kidney disease patients: a systematic review and meta-analysis

BACKGROUND

Metabolic acidosis accelerates the progression of chronic kidney disease (CKD) and increases the mortality rate. Whether oral alkali drug therapy benefits pre-dialysis CKD patients is controversial. We performed a meta-analysis of the effects of oral alkali drug therapy on major clinical outcomes in pre-dialysis CKD patients.

METHODS

We systematically searched MEDLINE using the Ovid, EMBASE, and Cochrane Library databases without language restriction. We included all eligible clinical studies that involved pre-dialysis CKD adults and compared those who received oral alkali drug therapy with controls.

RESULTS

A total of 18 eligible studies, including 14 randomized controlled trials and 4 cohort studies reported in 19 publications with 3695 participants, were included. Oral alkali drug therapy led to a 55% reduction in renal failure events (relative risk [RR]: 0.45; 95% confidence interval [CI]: 0.25-0.82), a rate of decline in the estimated glomerular filtration rate (eGFR) of 2.59 mL/min/1.73 m² per year (95% CI, 0.88-4.31). There was no significant effect on decline in eGFR events (RR: 0.34; 95% CI: 0.09-1.23), proteinuria (standardized mean difference: -0.32; 95% CI: -1.08 to 0.43), all-cause mortality events (RR: 0.90; 95% CI: 0.40-2.02) and cardiovascular (CV) events (RR: 1.03; 95% CI: 0.32-3.37) compared with the control groups.

CONCLUSION

Based on the available and low-to-moderate certainty evidence, oral alkali drug therapy might potentially reduce the risk of kidney failure events, but no benefit in reducing all-cause mortality events, CV events, decline in eGFR and porteninuria.

Measurement of Urinary Ammonium Using a Commercially Available Plasma Ammonium Assay

Background

Determination of urinary ammonium excretion is helpful in evaluating patients with acid-base disorders, chronic kidney disease, and nephrolithiasis. However, urinary ammonium levels are only measured by specialized laboratories in the United States, limiting widespread implementation. We evaluated the performance of a plasma ammonium assay to quantify urinary ammonium excretion and also determined ammonium stability under a variety of conditions.

Methods

An enzymatic plasma ammonium assay (Randox) was modified to measure urinary ammonium concentration. Urine samples were diluted 40-fold and then assayed on an Abbott Architect ci8200 analyzer. Assay precision, limit of quantitation, and linearity were determined. The method was compared against the formalin titration method, and stability studies were conducted at different temperatures and pH.

Results

After dilution, the assay had total precision of 18% at 2.54 mmol/L, 5% at 15.58 mmol/L, and 2% at 29.49 mmol/L, with a limit of quantitation of 2.92 mmol/L. Assay performance was linear in the range of 0.7-45 mmol/L. Method comparison against the formalin method showed a slope of 0.98 and intercept of -0.37 mmol/L. Urinary ammonium was determined to be stable for 48 hours at room temperature and for 9 days at 4°C and -20°C at pH 5.6-6.3. Ammonium was less stable at pH 3.8 and 8.5. When stored at -80°C, urinary ammonium was stable for at least 24 months.

Conclusions

The modified enzymatic plasma ammonium assay reliably quantifies urine ammonium at physiologic concentrations. It compares well with the formalin titration method and is suitable for routine clinical use on an automated chemistry analyzer.

Diagnosing metabolic acidosis in chronic kidney disease: importance of blood pH and serum anion gap

Metabolic acidosis is one of the most common complications of chronic kidney disease (CKD). It is associated with the progression of CKD, and many other functional impairments. Until recently, only serum bicarbonate levels have been used to evaluate acid-base changes in patients with reduced kidney function. However, recent emerging evidence suggests that nephrologists should reevaluate the clinical approach for diagnosing metabolic acidosis in patients with CKD based on two perspectives; pH and anion gap. Biochemistry and physiology textbooks clearly indicate that blood pH is the most important acid-base parameter for cellular function. Therefore, it is important to determine if the prognostic impact of hypobicarbonatemia varies according to pH level. A recent cohort study of CKD patients showed that venous pH modified the association between a low bicarbonate level and the progression of CKD. Furthermore, acidosis with a high anion gap has recently been recognized as an important prognostic factor, because veverimer, a nonabsorbable hydrochloride-binding polymer, has been shown to improve kidney function and decrease the anion gap. Acidosis with high anion gap frequently develops in later stages of CKD. Therefore, the anion gap is a time-varying factor and renal function (estimated glomerular filtration rate) is a time-dependent confounder for the anion gap and renal outcomes. Recent analyses using marginal structural models showed that acidosis with a high anion gap was associated with a high risk of CKD. Based on these observations, reconsideration of the clinical approach to diagnosing and treating metabolic acidosis in CKD may be warranted.

CKD in Recipients of Nonkidney Solid Organ Transplants: A Review

Chronic kidney disease (CKD) after solid organ transplant is a common clinical presentation, affecting 10% to 20% of liver, heart and lung transplant recipients and accounting for approximately 5% of the kidney transplant waiting list. The causes of CKD are different for different types of transplants and are not all, or even predominantly, due to calcineurin inhibitor toxicity, with significant heterogeneity particularly in liver transplant recipients. Many solid organ transplant recipients with advanced CKD benefit from kidney transplantation, but have a higher rate of death while waitlisted and higher mortality following transplant than the general kidney failure population. Recent organ allocation policies and proposals have attempted to address the appropriate identification and prioritization of candidates in need of a kidney transplant, either simultaneous with or following non-kidney transplant. Future research should focus on predictive factors for individuals identified at high risk for progression to kidney failure and death, and strategies to preserve kidney function and minimize the CKD burden in this unique patient population.

Time-updated anion gap and cardiovascular events in advanced CKD: a cohort study

Background

Studies examining associations between metabolic acidosis and cardiovascular events in chronic kidney disease (CKD) have shown conflicting results and have not differentiated between normal anion gap (hyperchloremic) acidosis and high anion gap acidosis. We aimed to examine the impact of normal and high anion gap acidosis, separately, on the risk of cardiovascular events among patients with CKD.

Methods

This retrospective cohort study included 1168 patients with an estimated glomerular filtration rate (eGFR) of 10–60 mL/min/1.73 m² and available data on anion gap. We analyzed the association of time-updated high anion gap (anion gap ≥9.2) with the rate of cardiovascular events using marginal structural models (MSMs) to account for time-dependent confounding. We also analyzed the association between time-updated normal anion gap acidosis (anion-gap-adjusted bicarbonate level ≤22.8 mEq/L) and cardiovascular events.

Results

The mean baseline eGFR of the cohort was 28 mL/min/1.73 m². The prevalence rates of high anion gap in CKD stages G3a, G3b, G4 and G5 were 20%, 16%, 27% and 46%, respectively. During a median follow-up period of 2.9 years, 132 patients developed cardiovascular events (3.3/100 patient-years). In MSMs, high anion gap was associated with a higher rate of cardiovascular events [hazard ratio (HR) 1.87; 95% confidence interval (95% CI) 1.13‒3.09; P = 0.02] and the composite of cardiovascular events or all-cause death (HR 3.28; 95% CI 2.19‒4.91; P < 0.001). Normal anion gap acidosis was not associated with cardiovascular events (HR 0.74; 95% CI, 0.47‒1.17; P = 0.2).

Conclusions

Among patients with advanced CKD, high anion gap was associated with an increased risk of cardiovascular events.

Serum bicarbonate is associated with kidney outcomes in autosomal dominant polycystic kidney disease

BACKGROUND

Metabolic acidosis accelerates progression of chronic kidney disease, but whether this is also true for autosomal dominant polycystic kidney disease (ADPKD) is unknown.

METHODS

Patients with ADPKD from the DIPAK (Developing Interventions to halt Progression of ADPKD) trial were included [n = 296, estimated glomerular filtration rate (eGFR) 50 ± 11 mL/min/1.73 m2, 2.5 years follow-up]. Outcomes were worsening kidney function (30% decrease in eGFR or kidney failure), annual eGFR change and height-adjusted total kidney and liver volumes (htTKV and htTLV). Cox and linear regressions were adjusted for prognostic markers for ADPKD [Mayo image class and predicting renal outcomes in ADPKD (PROPKD) scores] and acid-base parameters (urinary ammonium excretion).

RESULTS

Patients in the lowest tertile of baseline serum bicarbonate (23.1 ± 1.6 mmol/L) had a significantly greater risk of worsening kidney function [hazard ratio = 2.95, 95% confidence interval (CI) 1.21-7.19] compared with patients in the highest tertile (serum bicarbonate 29.0 ± 1.3 mmol/L). Each mmol/L decrease in serum bicarbonate increased the risk of worsening kidney function by 21% in the fully adjusted model (hazard ratio = 1.21, 95% CI 1.06-1.37). Each mmol/L decrease of serum bicarbonate was also associated with further eGFR decline (-0.12 mL/min/1.73 m2/year, 95% CI -0.20 to -0.03). Serum bicarbonate was not associated with changes in htTKV or htTLV growth.

CONCLUSIONS

In patients with ADPKD, a lower serum bicarbonate within the normal range predicts worse kidney outcomes independent of established prognostic factors for ADPKD and independent of urine ammonium excretion. Serum bicarbonate may add to prognostic models and should be explored as a treatment target in ADPKD.

Association of serum bicarbonate with graft survival and mortality in kidney transplant recipients

BACKGROUND

Metabolic acidosis is an independent risk factor for kidney disease progression with a high prevalence after kidney transplantation (KTx). Remarkably, it is still unclear if there is an impact of metabolic acidosis on graft function and death after KTx. Thus, we wanted to investigate if serum bicarbonate is associated with long-term graft outcome and mortality after KTx.

METHODS

We performed a single-center retrospective study including adult de novo KTx patients between 1999 and 2015. Cox proportional hazard model was used to analyze a possible association between time-dependent serum bicarbonate measurements and graft failure or death.

RESULTS

Four hundred thirty KTRs were included in the analysis with a mean age of 50.9 ± 13.4 years. Mean observation time was 4.7 ± 2.8 years. Two hundred eighty-four (66%) patients were male and 318 (74%) had received a deceased donor kidney transplant. Mean bicarbonate and eGFR levels 1 year post-transplant amounted to 22.9 ± 3.1 mEq/L and 61 ± 26 ml/min/1.73 m², respectively. Prevalence of metabolic acidosis was 31% 1 year after transplantation. Fourteen (3%) patients died and 31 (7%) suffered from graft failure. Higher bicarbonate levels were associated with significantly lower hazards for graft failure (Hazard Ratio (HR) = 0.88; 95% Confidence Interval (CI): 0.79-0.98) and mortality (HR = 0.79; 95% CI 0.66-0.93) after adjusting for potential confounders such as age, donor type and time-varying eGFR.

CONCLUSIONS

Our analysis showed that higher serum bicarbonate levels are positively associated with long-term graft and patient survival in kidney transplant recipients. Thus, serum bicarbonate may serve as a predictor and independent risk factor for graft and patient outcome after KTx as has been previously shown for patients with CKD.

Eubicarbonatemic Hydrogen Ion Retention and CKD Progression

Small-scale trials in patients with chronic kidney disease (CKD) 3-5 have shown that hypobicarbonatemic metabolic acidosis promotes progression of CKD. Accordingly, the 2012 KDIGO (Kidney Disease: Improving Global Outcomes) guideline suggests base administration to patients with CKD when serum bicarbonate concentration ([HCO₃ˉ]) is <22 mEq/L (~15% of non–dialysis-dependent patients with CKD). However, individuals with milder CKD largely maintain serum [HCO₃ˉ] within the normal range (eubicarbonatemia) and yet can manifest hydrogen ion (H⁺) retention. Limited data in eubicarbonatemic patients with CKD 2 suggest that base administration ameliorates CKD progression. Furthermore, most patients with moderate and advanced CKD maintain a normal serum [HCO₃ˉ], and of those, the vast majority most likely harbor masked H⁺ retention. The present review probes this expanded concept of metabolic acidosis of CKD: the eubicarbonatemic H⁺ retention or subclinical metabolic acidosis of CKD. It focuses on the high prevalence of the entity, its pathophysiologic features, its clinical course, and recent work on potential biomarkers of the condition. Further, it puts forward the urgent task of investigating definitively whether treatment with alkali of eubicarbonatemic H⁺ retention delays CKD progression. If proven true, such knowledge would trigger a paradigm shift in the indication for alkali therapy in CKD.

Metabolic Acidosis Is an Independent Risk Factor of Renal Progression in Korean Chronic Kidney Disease Patients: The KNOW-CKD Study Results

Background: We aimed to evaluate serum bicarbonate as a risk factor for renal progression, cardiovascular events, and mortality in Korean CKD patients.

Methods: We analyzed 1,808 participants from a Korean CKD cohort whose serum bicarbonate levels were measured at enrollment. Serum bicarbonate levels were categorized as low, lower normal, higher normal, and high (total carbon dioxide <22, 22–26, 26.1–29.9, and ≥30 mmol/L, respectively) groups. Metabolic acidosis was defined as a serum bicarbonate level <22 mmol/L. The primary outcome was renal events defined as doubling of serum creatinine, 50% reduction of eGFR from the baseline values, or development of end-stage kidney disease. The secondary outcome consisted of cardiovascular events and death. In addition, patients whose eGFR values were measured more than three times during the follow-up period were analyzed for eGFR decline. The rapid decline in eGFR was defined as lower than the median value of the eGFR slope.

Results: The mean serum bicarbonate level was 25.7 ± 3.7 mmol/L and 240 (13.2%) patients had metabolic acidosis. During the follow-up period of 55.2 ± 24.1 months, 545 (30.9%) patients developed renal events and 187 (10.6%) patients developed a composite of cardiovascular events and death. After adjustment, the low serum bicarbonate group experienced 1.27 times more renal events than the lower normal bicarbonate group [hazard ratio (HR): 1.27; 95% CI: 1.01–1.60, P = 0.043]. There was no significant association between the bicarbonate groups and the composite outcome of cardiovascular events and death. The low bicarbonate group showed a significantly rapid decline in eGFR [odds ratio (OR): 2.12; 95% CI: 1.39–3.22, P < 0.001] compared to the lower normal bicarbonate group.

Conclusions: Metabolic acidosis was significantly associated with increased renal events and a rapid decline in renal function in Korean predialysis CKD patients.

Association of Time-Updated Anion Gap With Risk of Kidney Failure in Advanced CKD: A Cohort Study

RATIONALE AND OBJECTIVE

High anion gap acidosis frequently develops in patients with advanced chronic kidney disease (CKD) and might be involved in kidney injury. Its impact on kidney outcomes, however, has not been well studied. We sought to examine the association between time-updated anion gap and the risk of kidney failure with replacement therapy (KFRT) among patients with advanced CKD.

STUDY DESIGN

Retrospective cohort study.

SETTING AND PARTICIPANTS

1,168 patients with CKD stages G3b-G5 who had available data on anion gap.

EXPOSURE

High time-updated anion gap defined as values ≥9.2 (top 25th percentile).

OUTCOMES

KFRT and death.

ANALYTICAL APPROACH

Marginal structural models (MSM) were fit to characterize the association between anion gap and study outcomes while accounting for potential time-dependent confounding.

RESULTS

The mean baseline eGFR of the study participants was 28 mL/min/1.73m². Over a median follow-up of 3.1 years, 317 patients progressed to KFRT (7.5/100 patient-years) and 146 died (3.5/100 patient-years). In the MSM, a high anion gap was associated with a higher rate of KFRT (hazard ratio [HR], 3.04; 95% confidence interval [CI], 1.94-4.75; P<0.001). This association was stronger in patients with baseline eGFR of <30 mL/min/1.73m² (P for interaction=0.05). High anion gap was also associated with a higher mortality rate (HR, 5.56; 95% CI, 2.95-10.5; P<0.001). Sensitivity analyses with different definitions of high anion gap showed similar results.

LIMITATIONS

Observational study design; selection bias due clinical indications for measuring anion gap.

CONCLUSION

Among patients with advanced CKD, high anion gap was associated with an increased risk of progression to KFRT and death.

Optimizing Diet to Slow CKD Progression

Due to the unique role of the kidney in the metabolism of nutrients, patients with chronic kidney disease (CKD) lose the ability to excrete solutes and maintain homeostasis. Nutrient intake modifications and monitoring of nutritional status in this population becomes critical, since it can affect important health outcomes, including progression to kidney failure, quality of life, morbidity, and mortality. Although there are multiple hemodynamic and metabolic factors involved in the progression and prognosis of CKD, nutritional interventions are a central component of the care of patients with non-dialysis CKD (ND-CKD) and of the prevention of overweight and possible protein energy-wasting. Here, we review the reno-protective effects of diet in adults with ND-CKD stages 3-5, including transplant patients.

Dietary acid load in children with chronic kidney disease

BACKGROUND/OBJECTIVES

Western diet is characterized by a high acid load that could generate various degrees of metabolic acidosis, of which at least the stronger forms are known to contribute to the progression of chronic kidney disease (CKD). The aim of this study was to estimate the potential renal acid load (PRAL) and acid base status in CKD patients attended at the Children's Hospital J.M. de los Ríos in Caracas, Venezuela from April 2015 to February 2016.

SUBJECTS/METHODS

Twenty-seven children with CKD were included. Diet composition was evaluated by a food frequency questionnaire and a 24-h intake reminder. PRAL was calculated by the Remer and Manz method. Laboratory tests included serum creatinine, electrolytes and venous gases.

RESULTS

Protein intake was above recommendations in 21 patients (78.6%). Average vegetable and fruit intake was 0.4 and 1.5 servings per day, respectively. Mean PRAL was 16 ± 10.7 mEq/day. PRAL correlated positively with energy (p = 0.005), protein (p = 0.001) and fat intake (p = 0.0001), daily servings of dairy (p = 0.04) meat (p = 0.001) and cereals (0.001) and negatively with vegetable intake (p = 0.04). Serum pH and bicarbonate were 7.3 ± 0.08 and 20.46 ± 4.5 mEq/L, respectively. Twenty-one patients (80.7%) with metabolic acidosis were treated with sodium bicarbonate.

CONCLUSIONS

Dietary pattern of Venezuelan children with CKD may constitute a risk factor for the progression of the disease by promoting metabolic acidosis via unfavorable dietary acid loads. PRAL should be assessed as a valuable guide for nutritional counseling in children with CKD.

Association of dietary acid load with serum bicarbonate in chronic kidney disease (CKD) patients

BACKGROUND/OBJECTIVES

Diet can affect the acid-base status depending on the balance between the intake of acid-inducing foods and base-inducing foods. The purpose of this study was to estimate the dietary acid load and evaluate its association with serum bicarbonate in patients with stages 3 and 4 chronic kidney disease.

SUBJECTS/METHODS

One hundred adults (aged ≥ 20 years) with chronic kidney disease (CKD) stages 3 and 4 were enrolled in a cross-sectional study. A food diary was used to estimate the animal and plant protein intakes, which were used in the potential renal acid load (PRAL) formula described by Remer and Manz. PRAL was divided into quartiles. Regression models unadjusted and adjusted for age, gender, body mass index, diabetes, systolic and diastolic blood pressure, creatinine clearance were performed using the stepwise regression method.

RESULTS

The median level (25th, 75th percentiles) of PRAL was 8.3 mEq/day (1.6, 15.6). The highest quartile of PRAL had a higher consumption of animal protein (77.8 ± 10.9%) and a reduced consumption of plant protein (22.2 ± 10.9%), compared to the lowest quartile (59.5 ± 18.6% animal protein, 40.5 ± 18.6% plant protein), p for trend <0.0001. In the adjusted analysis, a significant association was observed between the highest quartile of PRAL and serum bicarbonate in CKD patients compared to the lowest quartile (β: 2.07, 95% CI: 0.21-3.92). According to the multiple linear regression, for each increase of 1 unit of PRAL there was a reduction of 0.25 mmol/L in serum bicarbonate (HCO₃). Using the stepwise method, animal protein intake and PRAL were determinants of HCO₃ (r = 0.49).

CONCLUSIONS

In CKD patients of stages 3 and 4, the dietary acid load was associated with HCO₃. Limiting dietary acid load could be a complementary approach in the dietary treatment of CKD. In addition, studies are needed to analyze the effect of replacing animal protein with plant protein.

Dietary Plant Protein and Mortality Among Patients Receiving Maintenance Hemodialysis: A Cohort Study

RATIONALE & OBJECTIVE

Although greater dietary intake of protein has been associated with beneficial health effects among patients receiving maintenance hemodialysis (MHD), the effects of plant protein intake are less certain. We studied the association of the proportion of protein intake derived from plant sources with the risk of mortality among patients receiving MHD and explored factors that may modify these associations.

STUDY DESIGN

Prospective observational cohort study.

SETTING & PARTICIPANTS

1,119 Chinese hemodialysis patients aged over 18 years receiving MHD in 2014-2015.

PREDICTORS

The proportion of plant protein intake to total protein intake.

OUTCOMES

All-cause mortality and cardiovascular disease (CVD) mortality.

ANALYTICAL APPROACH

Segmented regression models were fit to examine the association of plant protein intake proportion with the risk of all-cause mortality and CVD mortality. Multivariable-adjusted Cox proportional and cause-specific hazards models were used to estimate the hazard ratios (HR) and 95% CI for these outcomes.

RESULTS

The means of plant protein intake normalized to ideal body weight and plant protein intake proportion were 0.6±0.2 (SD) g/kg per day and 0.538±0.134, respectively. During a median follow-up period of 28.0 months, 249 deaths occurred, with 146 of these deaths resulting from CVD. Overall, there was a U-shaped association between plant protein intake proportion and the risk of all-cause mortality, with an inflection point at 45%. Among patients with a plant protein intake proportion<45%, there was a 17% lower rate of mortality with each 5% greater plant protein intake proportion (HR, 0.83 [95% CI, 0.73-0.96]). Among patients with plant protein intake proportion≥45%, there was a 9% greater rate of mortality with each 5% greater plant protein intake proportion. A similar U-shaped association was observed for CVD mortality, with an inflection point at 44%.

LIMITATIONS

Observational study, potential unmeasured confounding.

CONCLUSIONS

There was a U-shaped association between plant protein intake proportion and the risk of all-cause and cardiovascular mortality in MHD patients. If confirmed, these findings suggest a potential avenue to improve outcomes in this patient population.

Metabolic acidosis is associated with increased risk of adverse kidney outcomes and mortality in patients with non-dialysis dependent chronic kidney disease: an observational cohort study

BACKGROUND

Management of chronic kidney disease (CKD) requires the management of risk factors, such as hypertension and albuminuria, that affect CKD progression. Identification of additional modifiable risk factors is necessary to develop new treatment strategies for CKD. We sought to quantify the association of metabolic acidosis with CKD progression and mortality in a large U.S. community-based cohort.

METHODS

In this longitudinal, retrospective cohort study we identified non-dialysis-dependent patients with stage 3‒5 CKD from Optum's de-identified integrated electronic health records. We selected cohorts of patients with confirmed metabolic acidosis or normal serum bicarbonate levels based on 2 consecutive serum bicarbonate values: 12 to < 22 mEq/L or 22-29 mEq/L, respectively, 28‒365 days apart. The primary composite outcome was ≥ 40 % decline in estimated glomerular filtration rate (eGFR), renal replacement therapy (chronic dialysis or kidney transplant), or all-cause mortality (DD40). Secondary outcomes included each component of the composite outcome. Cox proportional hazards models were used for the DD40 outcome and secondary outcomes, while logistic regression models were used for the DD40 outcome at 2 years.

RESULTS

A total of 51,558 patients qualified for the study. The unadjusted 2-year incidence of adverse renal and fatal outcomes was significantly worse among patients in the metabolic acidosis group vs. those who had normal serum bicarbonate levels: 48 % vs. 17 % for DD40, 10 % vs. 4 % for ≥ 40 % decline in eGFR, 20 % vs. 6 % for renal replacement therapy, and 31 % vs. 10 % for all-cause mortality (all P < 0.001). Over a ≤ 10-year period, for each 1-mEq/L increase in serum bicarbonate, the adjusted hazard ratio for DD40 was 0.926 (95 % confidence interval [CI], 0.922-0.930; P < 0.001); over a ≤ 2-year period, the adjusted odds ratio for DD40 was 0.873 (95 % CI, 0.866-0.879; P < 0.001).

CONCLUSIONS

In this large community cohort of patients with stage 3‒5 CKD, the presence of metabolic acidosis was a significant, independent risk factor for the composite adverse outcome of CKD progression, renal replacement therapy, and all-cause mortality (DD40).

Efficacy and Safety of Veverimer in the Treatment of Metabolic Acidosis Caused by Chronic Kidney Disease: A Meta-analysis

Metabolic acidosis is a common complication of chronic kidney disease (CKD). Veverimer is an orally administrated, free amine polymer with high capacity and binding selectivity to hydrochloric acid from the gastrointestinal tract. This study pooled the current evidence of the efficacy and safety of veverimer for the treatment of metabolic acidosis associated with CKD. We conducted a systematic literature search on PubMed, Embase, and Cochrane Central for relevant randomized controlled trials (RCTs) in June 2020. In this study, three RCTs with 548 patients were included in our analysis. The analysis revealed that veverimer was associated with increased bicarbonate level of patients (weight mean difference [WMD] 3.08, 95% confidence interval [CI] [2.40, 3.77], p < 0.001) and improved physical function compared with placebo measured by Kidney Disease and Quality of Life Short Form 36, question 3 (physical functioning domain) (KDQoL-PFD) score (WMD 5.25, 95% CI [1.58, 8.92], p = 0.005). For safety outcomes, both groups exhibited similar risks for developing headache, diarrhea, flatulence, and hyperkalemia. In conclusion, current clinical evidence indicates that veverimer is efficacious and safe against metabolic acidosis related to CKD compared with placebo. Further research comparing long-term veverimer use with traditional alkali therapy is needed.

Association of Pre-ESRD Serum Bicarbonate with Post-ESRD Mortality in Patients with Incident ESRD

BACKGROUND

Serum bicarbonate or total carbon dioxide (CO2) concentrations decline as chronic kidney disease (CKD) progresses and rise after dialysis initiation. While metabolic acidosis accelerates the progression of CKD and is associated with higher mortality among patients with end stage renal disease (ESRD), there are scarce data on the association of CO2 concentrations before ESRD transition with post-ESRD mortality.

METHODS

A historical cohort from the Transition of Care in CKD (TC-CKD) study includes 85,505 veterans who transitioned to ESRD from October 1, 2007, through March 31, 2014. After 1,958 patients without follow-up data, 3 patients with missing date of birth, and 50,889 patients without CO2 6 months prior to ESRD transition were excluded, the study population includes 32,655 patients. Associations between CO2 concentrations averaged over the last 6 months and its rate of decline during the 12 months prior to ESRD transition and post-ESRD all-cause, cardiovascular (CV), and non-CV mortality were examined by using hierarchical adjustment with Cox regression models.

RESULTS

The cohort was on average 68 ± 11 years old and included 29% Black veterans. Baseline concentrations of CO2 were 23 ± 4 mEq/L, and median (interquartile range) change in CO2 were -1.8 [-3.4, -0.2] mEq/L/year. High (≥28 mEq/L) and low (<18 mEq/L) CO2 concentrations showed higher adjusted mortality risk while there was no clear trend in the middle range. Consistent associations were observed irrespective of sodium bicarbonate use. There was also a U-shaped association between the change in CO2 and all-cause, CV, and non-CV mortality with the lowest risk approximately at -2.0 and 0.0 mEq/L/year among sodium bicarbonate nonusers and users, respectively, and the highest mortality was among patients with decline in CO2 >4 mEq/L/year.

CONCLUSION

Both high and low pre-ESRD CO2 levels (≥28 and <18 mEq/L) during 6 months prior to dialysis transition and rate of CO2 decline >4 mEq/L/year during 1 year before dialysis initiation were associated with greater post-ESRD all-cause, CV, and non-CV mortality. Further studies are needed to determine the optimal management of CO2 in patients with advanced CKD stages transitioning to ESRD.

Obesity and the Risk of Low Bicarbonate: A Cohort Study

Rationale & Objective

Acid retention may occur in the absence of overt metabolic acidosis; thus it is important to identify populations at risk. Because obesity may alter renal acid-base handling, we sought to determine whether overweight and obesity are associated with increased risk for low serum bicarbonate levels, suggesting metabolic acidosis.

Study Design

Retrospective cohort study.

Setting & Participants

Adult patients (n = 96,147) visiting outpatient clinics in the Bronx, NY, between January 1, 2010, and December 31, 2015.

Predictor

Body mass index (BMI).

Outcome

Low serum bicarbonate level (≤23 mEq/L).

Analytical Approach

Longitudinal analyses were conducted using mixed-effects models to examine associations of BMI with serum bicarbonate levels over time and Cox proportional hazards models to examine associations of BMI with incident low bicarbonate levels.

Results

During a median follow-up of 4.4 (interquartile range, 2.3-6.3) years, patients had a median of 8 serum bicarbonate measurements and 34,539 patients developed low bicarbonate levels. Higher BMI was associated with progressively lower serum bicarbonate levels, with attenuation of the association in the highest BMI groups, suggesting a J-shaped relationship. Compared with the reference group (BMI, 18.5 to <25 kg.m²), patients with BMIs of 25 to <30, 30 to <35, 35 to <40, and ≥40 kg/m² had HRs for incident low bicarbonate levels of 1.10 (95% CI, 1.05-1.14), 1.16 (95% CI, 1.11-1.21), 1.20 (95% CI, 1.14-1.26), and 1.15 (95% CI, 1.09-1.22). Results were similar after adjustment for serum urea nitrogen level and exclusion of patients with diabetes, hypertension, or estimated glomerular filtration rates < 60 mL/min/1.73 m².

Limitations

Arterial pH measurements were unavailable.

Conclusions

Higher BMI is independently associated with progressively greater risk for developing low serum bicarbonate levels, indicating likely metabolic acidosis. Further research should explore the causes of low bicarbonate levels in patients with overweight and obesity.

Relationship between mortality and use of sodium bicarbonate at the time of dialysis initiation: a prospective observational study

Background

Patients with chronic kidney disease often experience metabolic acidosis. Whether oral sodium bicarbonate can reduce mortality in patients with metabolic acidosis has been debated for years. Hence, this study was conducted to evaluate the utility of sodium bicarbonate in patients who will undergo dialysis therapy. In this study, we investigated the effect of oral sodium bicarbonate therapy on mortality in patients with end-stage kidney disease (ESKD) initiated on dialysis therapy.

Methods

We conducted an observational study of patients when they started dialysis therapy. There were 17 centres participating in the Aichi Cohort Study of Prognosis in Patients Newly Initiated into Dialysis. Data were available on patients’ sex, age, use of sodium bicarbonate, drug history, medical history, vital data, and laboratory data. We investigated whether patients on oral sodium bicarbonate for more than three months before dialysis initiation had a better prognosis than those without sodium bicarbonate therapy. The primary outcome was defined as all-cause mortality.

Results

The study included 1524 patients with chronic kidney disease who initiated dialysis between October 2011 and September 2013. Among them, 1030 were men and 492 women, with a mean age of 67.5 ± 13.1 years. Of these, 677 used sodium bicarbonate and 845 did not; 13.6% of the patients in the former group and 21.2% of those in the latter group died by March 2015 (p <  0.001). Even after adjusting for various factors, the use of sodium bicarbonate independently reduced mortality (p <  0.001).

Conclusions

The use of oral sodium bicarbonate at the time of dialysis initiation significantly reduced all-cause mortality in patients undergoing dialysis therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02330-0.