Effects of correction of metabolic acidosis on blood urea and bone metabolism in patients with mild to moderate chronic kidney disease: a prospective randomized single blind controlled trial

Efficacy and safety of oral sodium bicarbonate in kidney-transplant recipients and non-transplant patients with chronic kidney disease: a systematic review and meta-analysis

Introduction

We investigated the efficacy and safety of oral sodium bicarbonate in kidney-transplant recipients and non-transplant patients with chronic kidney disease (CKD), which are currently unclear.

Methods

PubMed, Cochrane Library, Embase, and Web of Science were searched for randomized controlled trials investigating the efficacy and safety of sodium bicarbonate versus placebo or standard treatment in kidney-transplant and non-transplant patients with CKD.

Results

Sixteen studies of kidney-transplant recipients (two studies, 280 patients) and non-transplant patients with CKD (14 studies, 1,380 patients) were included. With non-transplant patients, sodium bicarbonate slowed kidney-function declines (standardized mean difference [SMD]: 0.49, 95% confidence interval [CI]: 0.14-0.85, p = 0.006) within ≥12 months (SMD: 0.75 [95% CI: 0.12-1.38], p = 0.02), baseline-serum bicarbonate <22 mmol/L (SMD: 0.41 [95% CI: 0.19-0.64], p = 0.0004) and increased serum-bicarbonate levels (mean difference [MD]: 2.35 [95% CI: 1.40-3.30], p < 0.00001). In kidney-transplant recipients, sodium bicarbonate did not preserve graft function (SMD: -0.07 [95% CI: -0.30-0.16], p = 0.56) but increased blood pH levels (MD: 0.02 [95% CI: 0.00-0.04], p = 0.02). No significant adverse events occurred in the kidney-transplant or non-transplant patients (risk ratio [RR]: 0.89, [95% CI: 0.47-1.67], p = 0.72; and RR 1.30 [95% CI: 0.84-2.00], p = 0.24, respectively). However, oral sodium bicarbonate correlated with increased diastolic pressure and worsened hypertension and edema (MD: 2.21 [95% CI: 0.67-3.75], p = 0.005; RR: 1.44 [95% CI: 1.11-1.88], p = 0.007; and RR: 1.28 [95% CI: 1.00-1.63], p = 0.05, respectively).

Discussion

Oral sodium bicarbonate may slow kidney-function decline in non-transplant patients with CKD taking sodium bicarbonate supplementation for ≥12 months or a baseline serum bicarbonate level of <22 mmol/L, without preserving graft function in kidney-transplant recipients. Sodium bicarbonate may increase diastolic pressure, and elevate a higher incidence of worsening hypertension and edema.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42023413929.

Sodium Bicarbonate Treatment and Clinical Outcomes in Chronic Kidney Disease with Metabolic Acidosis: A Meta-Analysis

Key Points

Sodium bicarbonate for patients with CKD and metabolic acidosis leads to a significant improvement in kidney function. Treatment with sodium bicarbonate increases in mid-arm muscle circumference, indicating a positive effect on enhancing muscle mass. Sodium bicarbonate supplementation is associated with a higher risk of elevated systolic BP, marking a potential side effect.

Background

In patients with CKD, impaired kidney acid excretion leads to the onset of metabolic acidosis (MA). However, the evidence is not yet conclusive regarding the effects of sodium bicarbonate in treating CKD with MA.

Methods

Databases with PubMed, Embase, and the Cochrane Library were used to search for randomized controlled trials (RCTs) from the inception until November 11, 2023, to identify RCTs investigating the effect of sodium bicarbonate in participants with CKD and MA. The primary outcome was the change in eGFR. Secondary outcomes included hospitalization rates, change in systolic BP, all-cause mortality, and mid-arm muscle circumference. A random-effects model was applied for analysis, and subgroup, sensitivity analyses were also performed.

Results

Fourteen RCTs comprising 2037 patients demonstrated that sodium bicarbonate supplementation significantly improved eGFR (standardized mean difference [SMD], 0.33; 95% confidence interval [CI], 0.03 to 0.63; P = 0.03). The group receiving sodium bicarbonate had a lower hospitalization rate (odds ratio, 0.37; 95% CI, 0.25 to 0.55; P < 0.001). Higher mid-arm muscle circumference was observed with sodium bicarbonate treatment compared with those without (SMD, 0.23; 95% CI, 0.08 to 0.38; P = 0.003, I2<0.001). However, higher risk of elevated systolic BP was found with sodium bicarbonate treatment (SMD, 0.10; 95% CI, 0.01 to 0.20; P = 0.03). No significant difference in all-cause mortality was noted.

Conclusions

In patients with CKD and MA, sodium bicarbonate supplementation may provide potential benefits in preventing the deterioration of kidney function and increasing muscle mass. However, treatment may be associated with higher BP. Owing to the risk of bias stemming from the absence of double-blinded designs and inconsistencies in control group definitions across the studies, further research is crucial to verify these findings.

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.

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.

Effects of correcting metabolic acidosis on muscle mass and functionality in chronic kidney disease: a systematic review and meta-analysis

Metabolic acidosis unfavourably influences the nutritional status of patients with non-dialysis dependent chronic kidney disease (CKD) including the loss of muscle mass and functionality, but the benefits of correction are uncertain. We investigated the effects of correcting metabolic acidosis on nutritional status in patients with CKD in a systematic review and meta-analysis. A search was conducted in MEDLINE and the Cochrane Library from inception to June 2023. Study selection, bias assessment, and data extraction were independently performed by two reviewers. The Cochrane risk of bias tool was used to assess the quality of individual studies. We applied random effects meta-analysis to obtain pooled standardized mean difference (SMD) and 95% confidence intervals (CIs). We retrieved data from 12 intervention studies including 1995 patients, with a mean age of 63.7 ± 11.7 years, a mean estimated glomerular filtration rate of 29.8 ± 8.8 mL/min per 1.73 m2 , and 58% were male. Eleven studies performed an intervention with oral sodium bicarbonate compared with either placebo or with standard care and one study compared veverimer, an oral HCl-binding polymer, with placebo. The mean change in serum bicarbonate was +3.6 mEq/L in the intervention group and +0.4 mEq/L in the control group. Correcting metabolic acidosis significantly improved muscle mass assessed by mid-arm muscle circumference (SMD 0.35 [95% CI 0.16 to 0.54], P < 0.001) and functionality assessed with the sit-to-stand test (SMD -0.31 [95% CI -0.52 to 0.11], P = 0.003). We found no statistically significant effects on dietary protein intake, handgrip strength, serum albumin and prealbumin concentrations, and blood urea nitrogen. Correcting metabolic acidosis in patients with CKD improves muscle mass and physical function. Correction of metabolic acidosis should be considered as part of the nutritional care for patients with CKD.

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.

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.

Effect of Sodium Bicarbonate on Systolic Blood Pressure in CKD: A Systematic Review and Meta-Analysis

BACKGROUND

Individuals with CKD are at a higher risk of cardiovascular morbidity and mortality. Acidosis is positively correlated with CKD progression and elevated systolic BP. Sodium bicarbonate is an efficacious treatment of acidosis, although this may also increase systolic BP. In this systematic review and meta-analysis, we summarize the evidence evaluating systolic BP and antihypertensive medication change (which may indicate systolic BP change) in response to sodium bicarbonate therapy in individuals with CKD.

METHODS

Medical Literature Analysis and Retrieval System Online, Excerpta Medica database, Cumulative Index to Nursing and Allied Health Literature, Allied and Complementary Medicine Database, Cochrane Central Register of Controlled Trials, and World Health Organization (WHO) trials registry databases were searched for randomized control trials where sodium bicarbonate was compared with placebo/usual care in CKD stage G1-5 non-dialysis-dependent populations. Random effects meta-analyses were used to evaluate changes in systolic BP and BP-modifying drugs after sodium bicarbonate intervention.

RESULTS

Fourteen randomized control trials (2110 individuals, median follow-up 27 [interquartile range 97] weeks, mean age 60 [SD 10] years, mean systolic BP 136 [SD 17] mm Hg, mean eGFR 38 [SD 10] ml/min, mean serum bicarbonate 22 [SD 4] mmol/L) were eligible for inclusion. Meta-analysis suggested that sodium bicarbonate did not influence systolic BP in individuals with CKD stage G1-5. Results were consistent when stratifying by dose of sodium bicarbonate or duration of intervention. Similarly, there was no significant increase in the use of antihypertensive medication or diuretics in individuals taking sodium bicarbonate, whereas there was a greater decrease in antihypertensive medication use in individuals taking sodium bicarbonate compared with controls.

CONCLUSIONS

Our results suggest, with moderate certainty, that sodium bicarbonate supplementation does not adversely affect systolic BP in CKD or negatively influence antihypertensive medication requirements.

Clinical Consequences of Metabolic Acidosis-Muscle

Metabolic acidosis is common in people with chronic kidney disease and can contribute to functional decline, morbidity, and mortality. One avenue through which metabolic acidosis can result in these adverse clinical outcomes is by negatively impacting skeletal muscle; this can occur through several pathways. First, metabolic acidosis promotes protein degradation and impairs protein synthesis, which lead to muscle breakdown. Second, metabolic acidosis hinders mitochondrial function, which decreases oxidative phosphorylation and reduces energy production. Third, metabolic acidosis directly limits muscle contraction. The purpose of this review is to examine the specific mechanisms of each pathway through which metabolic acidosis affects muscle, the impact of metabolic acidosis on physical function, and the effect of treating metabolic acidosis on functional outcomes.

Effects of Oral Bicarbonate Supplementation on the Cardiovascular Risk Factors and Serum Nutritional Markers in Non-Dialysed Chronic Kidney Disease Patients

Background and Objectives: Kidneys play a key role in maintaining the acid−base balance. The aim of this study was to evaluate the effect of a 3-month oral sodium bicarbonate administration on arterial wall stiffness, arterial pressure and serum nutritional markers in non-dialysed patients with chronic kidney disease (CKD) stages 3−5 and metabolic acidosis. Methods: Eighteen CKD patients with eGFR < 45 mL/min/1.73 m2 and capillary blood bicarbonate (HCO3) < 22 mmol/L were enrolled in this single-centre, prospective study. Anthropometric parameters, pulse wave velocity, 24-h ambulatory blood pressure measurements, blood and urine parameters were assessed at the beginning and at the end of the study. The patients received supplementation with 2 g of sodium bicarbonate daily for three months. Results: A significant increase of pH: 7.32 ± 0.06 to 7.36 ± 0.06; p = 0.025, HCO3 from 18.7 mmol/L (17.7−21.3) to 22.2 mmol/L (20.2−23.9); p < 0.001 and a decrease in base excess from −6.0 ± 2.4 to −1.9 ± 3.1 mmol/L; p < 0.001 were found. An increase in serum total protein from 62.7 ± 6.9 to 65.8 ± 6.2; p < 0.013 and albumin from 37.3 ± 5.4 to 39.4 ± 4.8; p < 0.037 but, also, NT-pro-BNP (N-Terminal Pro-B-Type Natriuretic Peptide) from 794.7 (291.2−1819.0) to 1247.10 (384.7−4545.0); p < 0.006, CRP(C Reactive Protein) from 1.3 (0.7−2.9) to 2.8 (1.1−3.1); p < 0.025 and PTH (parathyroid hormone) from 21.5 ± 13.7 to 27.01 ± 16.3; p < 0.006 were observed, as well as an increase in erythrocyte count from 3.4 ± 0.6 to 3.6 ± 0.6; p < 0.004, haemoglobin from 10.2 ± 2.0 to 11.00 ± 1.7; p < 0.006 and haematocrit from 31.6 ± 6.00 to 33.6 ± 4.8; p < 0.009. The mean eGFR during sodium bicarbonate administration did not change significantly: There were no significant differences in pulse wave velocity or in the systolic and diastolic BP values. Conclusion: The administration of sodium bicarbonate in non-dialysed CKD patients in stages 3−5 improves the parameters of metabolic acidosis and serum nutritional markers; however, it does not affect the blood pressure and vascular stiffness.

Acute catabolic bone metabolism response to exercise in young and older adults: A narrative review

Exercise is recommended for cardiometabolic benefits and to preserve or improve bone health, especially for older adults at increased risk of fracture. However, exercise interventions have modest benefits on areal bone mineral density (aBMD), and exercise can lead to bone loss in young athletes under certain conditions. In this narrative review, we discuss evidence for a disruption in calcium homeostasis during exercise that may diminish the skeletal benefits of exercise. Topics include 1) a general overview of the effects of exercise on aBMD; 2) discussion of the exercise-induced disruption in calcium homeostasis; 3) factors that influence the magnitude of the exercise-induced disruption in calcium homeostasis, including age, sex, and exercise mode, intensity, and duration; 4) oral calcium supplementation to minimize the exercise-induced disruption in calcium homeostasis; and 5) potential for exercise-induced increase in parathyroid hormone to be both catabolic and anabolic to bone.

Muscle-bone axis in children with chronic kidney disease: current knowledge and future perspectives

Bone and muscle tissue are developed hand-in-hand during childhood and adolescence and interact through mechanical loads and biochemical pathways forming the musculoskeletal system. Chronic kidney disease (CKD) is widely considered as both a bone and muscle-weakening disease, eventually leading to frailty phenotype, with detrimental effects on overall morbidity. CKD also interferes in the biomechanical communication between two tissues. Pathogenetic mechanisms including systemic inflammation, anorexia, physical inactivity, vitamin D deficiency and secondary hyperparathyroidism, metabolic acidosis, impaired growth hormone/insulin growth factor 1 axis, insulin resistance, and activation of renin-angiotensin system are incriminated for longitudinal uncoordinated loss of bone mineral content, bone strength, muscle mass, and muscle strength, leading to mechanical impairment of the functional muscle-bone unit. At the same time, CKD may also interfere in the biochemical crosstalk between the two organs, through inhibiting or stimulating the expression of certain osteokines and myokines. This review focuses on presenting current knowledge, according to in vitro, in vivo, and clinical studies, concerning the pathogenetic pathways involved in the muscle-bone axis, and suggests approaches aimed at preventing bone loss and muscle wasting in the pediatric population. Novel therapeutic targets for preserving musculoskeletal health in the context of CKD are also discussed.

Physiologic Regulation of Systemic Klotho Levels by Renal CaSR Signaling in Response to CaSR Ligands and pH o

BACKGROUND

The kidney is the source of sKlotho and kidney-specific loss of Klotho leads to a phenotype resembling the premature multiorgan failure phenotype in Klotho-hypomorphic mice ( kl/kl mice). Klotho and the Ca-sensing receptor (CaSR) are highly expressed in the distal convoluted tubule (DCT). The physiologic mechanisms that regulate sKlotho levels are unknown.

METHODS

We measured sKlotho in WT and tubule-specific CaSR -/- (TS-CaSR -/- ) mice treated with calcimimetics, alkali, or acid, and Klotho shed from minced mouse kidneys, and from HEK-293 cells expressing the CaSR and Klotho, in response to calcimimetics, calcilytics, alkalotic and acidic pH, and ADAM protease inhibitors. The CaSR, Klotho, and ADAM10 were imaged in mouse kidneys and cell expression systems using confocal microscopy.

RESULTS

The CaSR, Klotho, and ADAM10 colocalize on the basolateral membrane of the DCT. Calcimimetics and HCO 3 increase serum sKlotho levels in WT but not in CaSR -/- mice, and acidic pH suppresses sKlotho levels in WT mice. In minced kidneys and cultured cells, CaSR activation with high Ca, calcimimetics, or alkali increase shed Klotho levels via ADAM10, as demonstrated using the ADAM10 inhibitor GI254023X and siRNA. In cultured cells, the CaSR, Klotho, and ADAM10 form cell surface aggregates that disperse after CaSR activation.

CONCLUSIONS

We identify a novel physiologic mechanism for regulation of sKlotho levels by the renal CaSR-ADAM10-Klotho pathway. We show that CaSR activators, including alkali, increase renal CaSR-stimulated Klotho shedding and predict that this mechanism is relevant to the effects of acidosis and alkali therapy on CKD progression.

A Systematic Review and Meta-Analysis on Effects of Bicarbonate Therapy on Kidney Outcomes

Aim

Preclinical studies suggest treatment of metabolic acidosis may slow chronic kidney disease (CKD) progression. This systematic review aimed to summarize evidence from randomized controlled trials (RCTs) concerning the benefits and risks of bicarbonate therapy on kidney outcomes.

Methods

Medline, EMBASE, and Cochrane databases were searched for RCTs with ≥3 months’ follow-up in patients with CKD (estimated glomerular filtration rate [eGFR] ≤60 ml/min per 1.73 m² and/or proteinuria) comparing the effects of sodium bicarbonate with placebo/no study medication on kidney outcomes. The primary outcome was change from baseline to last measurement in kidney function measured as either eGFR or creatinine clearance. Treatment effects were summarized using random-effects meta-analysis.

Results

Fifteen trials (2445 participants, median follow-up 12 months) were eligible for inclusion. Compared with placebo or no study medication, sodium bicarbonate retarded the decline in kidney function (standardized mean difference [SMD]: 0.26; 95% confidence interval [CI]: 0.13–0.40; I² = 50%, low certainty evidence), and reduced the risk of end-stage kidney failure (risk ratio [RR]: 0.53; 95% CI 0.32–0.89; I² = 69%, low certainty evidence). The effect of sodium bicarbonate on proteinuria (SMD: −0.09; 95% CI −0.27 to 0.09; I² = 28%, very low certainty evidence), systolic blood pressure (weighted mean difference [WMD]: −0.57 mm Hg; 95% CI −2.32 to 1.18; I² = 0%, low certainty evidence), all-cause death (RR: 0.81; 95% CI: 0.39–1.68; I² = 30%; very low certainty evidence) and edema (RR: 1.16; 95% CI: 0.90–1.50; I² = 28%; low certainty evidence) were uncertain.

Conclusion

Sodium bicarbonate may slow CKD progression. Adequately powered randomized trials are required to evaluate the benefits and risks of sodium bicarbonate in CKD.

Chronic Metabolic Acidosis in Chronic Kidney Disease

BACKGROUND

Metabolic acidosis may be diagnosed as chronic (cMA) if it persists for at least 5 days, although an exact definition has not been provided by any guidelines yet. The most common cause is CKD; numerous less-known diseases can also account for cMA.

SUMMARY

In recent years, CKD-associated cMA has been proposed to induce several clinical complications. The aim of the article was to assess the current clinical evidence for complications and the respective management of CKD-associated cMA. In summary, cMA in CKD most likely promotes protein degradation and loss of bone mineral density. It aggravates CKD progression as indicated by experimental and (partly) clinical data. Therefore, cMA control must be recommended. Besides oral bicarbonate, dietary interventions potentially offer an alternative. Veverimer is a future option for cMA control; further systematic data are needed.

CONCLUSIONS

The most common cause of cMA is CKD. CKD-associated cMA most likely induces a negative protein balance; the exact role on bone metabolism remains uncertain. It presumably aggravates CKD progression. cMA control is recommendable; the serum bicarbonate target level should range around 24 mEq/L. Veverimer may be established as future option for cMA control; further systematic data are needed.

Complications of metabolic acidosis and alkalinizing therapy in chronic kidney disease patients: a clinician-directed organ-specific primer

Chronic kidney disease is prevalent, affecting more than one in ten adults. In this population, metabolic acidosis is considered a key underlying pathophysiological feature, tying together bone mineral disorders, sarcopenia, insulin resistance, vascular calcification, pro-inflammatory and pro-thrombotic states. This review aims to address the paucity of literature on alkalinizing agents, a promising treatment option that has known adverse effects.

Sodium bicarbonate to improve physical function in patients over 60 years with advanced chronic kidney disease: the BiCARB RCT

BACKGROUND

Advanced chronic kidney disease is common in older people and is frequently accompanied by metabolic acidosis. Oral sodium bicarbonate is used to treat this acidosis, but evidence is lacking on whether or not this provides a net gain in health or quality of life for older people.

OBJECTIVES

The objectives were to determine whether or not oral bicarbonate therapy improves physical function, quality of life, markers of renal function, bone turnover and vascular health compared with placebo in older people with chronic kidney disease and mild acidosis; to assess the safety of oral bicarbonate; and to establish whether or not oral bicarbonate therapy is cost-effective in this setting.

DESIGN

A parallel-group, double-blind, placebo-controlled randomised trial.

SETTING

The setting was nephrology and geriatric medicine outpatient departments in 27 UK hospitals.

PARTICIPANTS

Participants were adults aged ≥ 60 years with advanced chronic kidney disease (glomerular filtration rate category 4 or 5, not on dialysis) with a serum bicarbonate concentration of < 22 mmol/l.

INTERVENTIONS

Eligible participants were randomised 1 : 1 to oral sodium bicarbonate or matching placebo. Dosing started at 500 mg three times daily, increasing to 1 g three times daily if the serum bicarbonate concentration was < 22 mmol/l at 3 months.

MAIN OUTCOME MEASURES

The primary outcome was the between-group difference in the Short Physical Performance Battery score at 12 months, adjusted for baseline. Other outcome measures included generic and disease-specific health-related quality of life, anthropometry, 6-minute walk speed, grip strength, renal function, markers of bone turnover, blood pressure and brain natriuretic peptide. All adverse events were recorded, including commencement of renal replacement therapy. For the health economic analysis, the incremental cost per quality-adjusted life-year was the main outcome.

RESULTS

In total, 300 participants were randomised, 152 to bicarbonate and 148 to placebo. The mean age of participants was 74 years and 86 (29%) were female. Adherence to study medication was 73% in both groups. A total of 220 (73%) participants were assessed at the 12-month visit. No significant treatment effect was evident for the primary outcome of the between-group difference in the Short Physical Performance Battery score at 12 months (-0.4 points, 95% confidence interval -0.9 to 0.1 points; p = 0.15). No significant treatment benefit was seen for any of the secondary outcomes. Adverse events were more frequent in the bicarbonate arm (457 vs. 400). Time to commencement of renal replacement therapy was similar in both groups (hazard ratio 1.22, 95% confidence interval 0.74 to 2.02; p = 0.43). Health economic analysis showed higher costs and lower quality of life in the bicarbonate arm at 1 year, with additional costs of £564 (95% confidence interval £88 to £1154) and a quality-adjusted life-year difference of -0.05 (95% confidence interval -0.08 to -0.01); placebo dominated bicarbonate under all sensitivity analyses for incremental cost-effectiveness.

LIMITATIONS

The trial population was predominantly white and male, limiting generalisability. The increment in serum bicarbonate concentrations achieved was small and a benefit from larger doses of bicarbonate cannot be excluded.

CONCLUSIONS

Oral sodium bicarbonate did not improve a range of health measures in people aged ≥ 60 years with chronic kidney disease category 4 or 5 and mild acidosis, and is unlikely to be cost-effective for use in the NHS in this patient group. Once other current trials of bicarbonate therapy in chronic kidney disease are complete, an individual participant meta-analysis would be helpful to determine which subgroups, if any, are more likely to benefit and which treatment regimens are more beneficial.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN09486651 and EudraCT 2011-005271-16. The systematic review is registered as PROSPERO CRD42018112908.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 24, No. 27. See the NIHR Journals Library website for further project information.

Effects of Treatment of Metabolic Acidosis in CKD: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVES

Metabolic acidosis is associated with progression of CKD and has significant adverse effects on muscle and bone. A systematic review and meta-analysis was conducted to evaluate the benefits and risks of metabolic acidosis treatment with oral alkali supplementation or a reduction of dietary acid intake in those with CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

MEDLINE, Embase, and Cochrane CENTRAL were searched for relevant trials in patients with stage 3-5 CKD and metabolic acidosis (<22 mEq/L) or low-normal serum bicarbonate (22-24 mEq/L). Data were pooled in a meta-analysis with results expressed as weighted mean difference for continuous outcomes and relative risk for categorical outcomes with 95% confidence intervals (95% CIs), using a random effects model. Study quality and strength of evidence were assessed using Cochrane risk of bias and the Grading of Recommendations Assessment, Development and Evaluation criteria.

RESULTS

Fourteen clinical trials were included (n=1394 participants). Treatment of metabolic acidosis with oral alkali supplementation or a reduction of dietary acid intake increased serum bicarbonate levels (14 studies, 1378 patients, mean difference 3.33 mEq/L, 95% CI, 2.37 to 4.29) and resulted in a slower decline in eGFR (13 studies, 1329 patients, mean difference -3.28 ml/min per 1.73 m2, 95% CI, -4.42 to -2.14; moderate certainty) and a reduction in urinary albumin excretion (very-low certainty), along with a reduction in the risk of progression to ESKD (relative risk, 0.32; 95% CI, 0.18 to 0.56; low certainty). Oral alkali supplementation was associated with worsening hypertension or the requirement for increased antihypertensive therapy (very-low certainty).

CONCLUSIONS

Low-to-moderate certainty evidence suggest that oral alkali supplementation or a reduction in dietary acid intake may slow the rate of kidney function decline and potentially reduce the risk of ESKD in patients with CKD and metabolic acidosis.

Impact of Recent Clinical Trials on Nephrology Practice: Are We in a Stagnant Era?

BACKGROUND

Although renal replacement therapy prevents death from uremia, survival among patients with acute and chronic kidney diseases (CKD) remains an imperative concern. The expected life span of US dialysis patients 60-64 years of age is approximately 4.5 years; this is similar to that of patients with lung cancer. Despite substantial progress in many medical specialties over the past decades (e.g., notable reductions in myocardial infarction, stroke, and mortality rates in the general population), survival among dialysis patients has not improved significantly over the same period. A few decades ago, HIV infection and AIDS were pretty much a death sentence. Because of progress in HIV treatment, now it can be controlled with a daily pill, and ongoing research is pushing treatment even further and controls the virus with longer-acting treatment. A cure is no longer impossible for HIV and other viral infections such as hepatitis B and C and many malignancies, but so far there is no cure for CKD.

SUMMARY

Billions of dollars have been spent on kidney disease research in the past decades, with no tangible progress in clinical practice. The challenges of improving the quantity and quality of trials in nephrology are enormous. The number of randomized controlled trials (RCTs) published in nephrology is lower than that in other medical subspecialties, and most of the big RCTs in nephrology yield negative results. Nephrology studies evaluating hard clinical endpoints or surrogate endpoints are scarce.

KEY MESSAGE

Herein we discuss the slow progress in nephrology research that has impacted clinical practice over the last couple of decades and highlight the major obstacles, challenges, and potential solutions.

Aiming for the optimal bicarbonate prescription for maintenance hemodialysis therapy in end-stage renal disease

INTRODUCTION

Acidemia and alkalemia, as a result of gradual depletion of the body's buffers followed by rapid repletion during hemodialysis (HD), are linked to adverse consequences. We examined the acid-base status with dialysis bath of higher bicarbonate (HC03^- ) concentration or standard HC03^- bath plus oral HC03^- supplementation.

METHODS

A total of 60 stable HD patients (pts) were evaluated according to their pre-dialysis acid-base status both before the first and the second session of the week dialyzed against standard base dialysate of 35 mmol/L. Those who presented predialysis HC03^- <22 mmol/L (25 pts) were assigned to dialysis against bath of increased HC03^- levels (37 mmol/L) for 2 weeks (period A) and subsequently to dialysis with the standard dialysate bath plus daily oral sodium bicarbonate at a dose of 5 g/day for 2 weeks (period B). Pre and post-dialysis acid-base status at each study period and relevant laboratory tests were recorded.

FINDINGS

Pre-dialysis acid-base values were similar between the first and the second dialysis session. Twenty-five points had pre-dialysis pH <7.35, while 42 (the younger ones) presented pre-dialysis HC03^- <22 mmol/L. After dialysis session 18 pts had pH >7.45. Comparing the two study periods, interdialytic weight was similar, pre-dialysis HC03^- levels were improved with oral bicarbonate, while post-dialysis HC03^- were higher during period A. Three pts could not tolerate the symptoms of alkalemia during period A.

DISCUSSION

The impact of conventional HC03^- concentrations of 35 mmol/L results in a considerable degree of pre-dialysis acidemia. Increasing the HC03^- in bath results in more prominent post-dialysis alkalemia, however, it is not sufficient to maintain acid-base status during the interdialytic period. Oral bicarbonate supplement at a dose of 5 g/day (divided in three daily doses) results in a more balanced acid-base status, avoiding post-dialysis alkalemia.

Oral Bicarbonate Therapy in Non-Haemodialysis Dependent Chronic Kidney Disease Patients: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Metabolic acidosis is a common complication in chronic kidney disease (CKD) patients, and is associated with an accelerated decline in renal function. Oral bicarbonate therapy has been used to counteract metabolic acidosis in CKD for decades. However, until recently, there have been very few intervention studies testing the effectiveness of bicarbonate therapy at improving metabolic acidosis or its consequences in patients with CKD. In this systematic review and meta-analysis, we aimed to examine the outcomes of all published randomised controlled trials (RCTs) that investigated the effect of oral bicarbonate therapy in adults with CKD. Ovid MEDLINE^®, EMBASE^® and Cochrane Library were searched in mid-October 2018 for English literature, with no restrictions applied to the publication status or date. Seven RCTs that recruited 815 participants met our inclusion criteria after full text review. Oral bicarbonate supplementation resulted in a slightly higher estimated glomerular filtration rate (eGFR) (mean difference 3.1 mL/min per 1.73 m²; 95% CI 1.3–4.9) and serum bicarbonate levels (mean difference 3.4 mmol/L; 95% CI 1.9–4.9) at the end of follow-up (three months to five years) compared to those given placebo or conventional CKD treatment. When limited to studies reporting outcomes at one year, the positive effect of oral bicarbonate therapy on eGFR was attenuated. There were no significant treatment effects in other parameters such as systolic blood pressure (BP) and weight. These findings should be interpreted with caution and further trial evidence is needed to establish the net overall benefit or harm of oral bicarbonate therapy in CKD.

Chronic Kidney Disease and Dietary Measures to Improve Outcomes

Chronic kidney disease is an ongoing deterioration of renal function that often progresses to end-stage renal disease. Management goals in children include slowing disease progression, prevention and treatment of complications, and optimizing growth, development, and quality of life. Nutritional management is critically important to achieve these goals. Control of blood pressure, proteinuria, and metabolic acidosis with dietary and pharmacologic measures may slow progression of chronic kidney disease. Although significant progress in management has been made, further research is required to resolve many outstanding controversies. We review recent developments in pediatric chronic kidney disease, focusing on dietary measures to improve outcomes.

Tolerance to Sodium in Patients With CKD-Induced Metabolic Acidosis: Does the Accompanying Anion Matter?

Patients with chronic kidney disease (CKD) continue to produce endogenous acids but have a reduction in net acid excretion, resulting in a primary decrease in serum bicarbonate concentration, which is termed chronic metabolic acidosis. Recent prospective studies, along with retrospective cohort analyses, demonstrate a higher risk for CKD progression with untreated metabolic acidosis. To normalize serum bicarbonate levels, acidemic patients are often treated with sodium bicarbonate (NaHCO₃) or sodium citrate, which have been shown to slow the progression of CKD. However, studies using this approach have routinely excluded patients with common sodium-sensitive comorbid conditions, such as poorly controlled hypertension, congestive heart failure, volume overload, or edema. This article examines the effect of the anion that accompanies sodium delivered with these therapies. Do the negative effects on blood pressure (BP) and sodium retention, as measured by an increase in edema, weight gain, and congestive heart failure, observed with oral administration of sodium chloride (NaCl) differ when a similar amount of sodium is given with bicarbonate or citrate in this patient population? A review of the literature suggests that NaHCO₃ does not increase BP or sodium retention when administered to patients with CKD during a concurrent severe NaCl dietary restriction (∼10 mEq/d). However, this degree of NaCl restriction is feasible only under strict control in clinical research environments. In contrast, when NaHCO₃ is given to patients without severe dietary NaCl restriction, there is an increase in BP and sodium retention. Thus, unless patients with CKD can tolerate a diet virtually devoid of NaCl, additional sodium, regardless of the accompanying anion, appears to increase BP and sodium retention.

Oral alkali therapy and the management of metabolic acidosis of chronic kidney disease: A narrative literature review

Chronic metabolic acidosis is a common complication seen in advanced chronic kidney disease (CKD). There is currently no consensus on its management in the Republic of Ireland. Recent trials have suggested that appropriate active management of metabolic acidosis through oral alkali therapy and modified diet can have a deterring impact on CKD progression. The potential benefits of treatment include preservation of bone health and improvement in muscle function; however, present data is limited. This review highlights the current evidence, available primarily from randomised control trials (RCTs) over the last decade, in managing the metabolic acidosis of CKD and outlines ongoing RCTs that are promising. An economic perspective is also briefly discussed to support decision-making.

Metabolic Acidosis and Subclinical Metabolic Acidosis in CKD

Metabolic acidosis is not uncommon in CKD and is linked with bone demineralization, muscle catabolism, and higher risks of CKD progression and mortality. Clinical practice guidelines recommend maintaining serum total CO₂ at ≥22 mEq/L to help prevent these complications. Although a definitive trial testing whether correcting metabolic acidosis improves clinical outcomes has not been conducted, results from small, single-center studies support this notion. Furthermore, biologic plausibility supports the notion that a subset of patients with CKD have acid-mediated organ injury despite having a normal serum total CO₂ and might benefit from oral alkali before overt acidosis develops. Identifying these individuals with subclinical metabolic acidosis is challenging, but recent results suggest that urinary acid excretion measurements may be helpful. The dose of alkali to provide in this setting is unknown as well. The review discusses these topics and the prevalence and risk factors of metabolic acidosis, mechanisms of acid-mediated organ injury, results from interventional studies, and potential harms of alkali therapy in CKD.

Management of the Metabolic Acidosis of Chronic Kidney Disease

Subjects with CKD and reduced glomerular filtration rate are at risk for chronic metabolic acidosis, and CKD is its most common cause. Untreated metabolic acidosis, even in its mildest forms, is associated with increased mortality and morbidity and should therefore be treated. If reduced glomerular filtration rate or the tubule abnormality causing chronic metabolic acidosis cannot be corrected, it is typically treated with dietary acid (H⁺) reduction using Na⁺-based alkali, usually NaHCO₃. Dietary H⁺ reduction can also be accomplished with the addition of base-producing foods such as fruits and vegetables and limiting intake of H⁺-producing foods like animal-sourced protein. The optimal dose of Na⁺-based alkali that prevents the untoward effects of metabolic acidosis while minimizing adverse effects and the appropriate combination of this traditional therapy with dietary strategies remain to be determined by ongoing studies. Recent emerging evidence supports a phenomenon of H⁺ retention, which precedes the development of metabolic acidosis by plasma acid-base parameters, but further studies will be needed to determine how best to identify patients with this phenomenon and whether they too should be treated with dietary H⁺ reduction.

Bicarbonate Concentration, Acid-Base Status, and Mortality in the Health, Aging, and Body Composition Study

BACKGROUND AND OBJECTIVES

Low serum bicarbonate associates with mortality in CKD. This study investigated the associations of bicarbonate and acid-base status with mortality in healthy older individuals.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We analyzed data from the Health, Aging, and Body Composition Study, a prospective study of well functioning black and white adults ages 70-79 years old from 1997. Participants with arterialized venous blood gas measurements (n=2287) were grouped into <23.0 mEq/L (low), 23.0-27.9 mEq/L (reference group), and ≥28.0 mEq/L (high) bicarbonate categories and according to acid-base status. Survival data were collected through February of 2014. Mortality hazard ratios (HRs; 95% confidence intervals [95% CIs]) in the low and high bicarbonate groups compared with the reference group were determined using Cox models adjusted for demographics, eGFR, albuminuria, chronic obstructive pulmonary disease, smoking, and systemic pH. Similarly adjusted Cox models were performed according to acid-base status.

RESULTS

The mean age was 76 years, 51% were women, and 38% were black. Mean pH was 7.41, mean bicarbonate was 25.1 mEq/L, 11% had low bicarbonate, and 10% had high bicarbonate. Mean eGFR was 82.1 ml/min per 1.73 m(2), and 12% had CKD. Over a mean follow-up of 10.3 years, 1326 (58%) participants died. Compared with the reference group, the mortality HRs were 1.24 (95% CI, 1.02 to 1.49) in the low bicarbonate and 1.03 (95% CI, 0.84 to 1.26) in the high bicarbonate categories. Compared with the normal acid-base group, the mortality HRs were 1.17 (95% CI, 0.94 to 1.47) for metabolic acidosis, 1.21 (95% CI, 1.01 to 1.46) for respiratory alkalosis, and 1.35 (95% CI, 1.08 to 1.69) for metabolic alkalosis categories. Respiratory acidosis did not associate with mortality.

CONCLUSIONS

In generally healthy older individuals, low serum bicarbonate associated with higher mortality independent of systemic pH and potential confounders. This association seemed to be present regardless of whether the cause of low bicarbonate was metabolic acidosis or respiratory alkalosis. Metabolic alkalosis also associated with higher mortality.

Low Serum Bicarbonate Predicts Residual Renal Function Loss in Peritoneal Dialysis Patients

Low residual renal function (RRF) and serum bicarbonate are associated with adverse outcomes in peritoneal dialysis (PD) patients. However, a relationship between the 2 has not yet been determined in these patients. Therefore, this study aimed to investigate whether low serum bicarbonate has a deteriorating effect on RRF in PD patients.This prospective observational study included a total of 405 incident patients who started PD between January 2000 and December 2005. We determined risk factors for complete loss of RRF using competing risk methods and evaluated the effects of time-averaged serum bicarbonate (TA-Bic) on the decline of RRF over the first 3 years of dialysis treatment using generalized linear mixed models.During the first 3 years of dialysis, 95 (23.5%) patients became anuric. The mean time until patients became anuric was 20.8 ± 9.0 months. After adjusting for multiple potentially confounding covariates, an increase in TA-Bic level was associated with a significantly decreased risk of loss of RRF (hazard ratio per 1 mEq/L increase, 0.84; 0.75-0.93; P = 0.002), and in comparison to TA-Bic ≥ 24 mEq/L, TA-Bic < 24 mEq/L conferred a 2.62-fold higher risk of becoming anuric. Furthermore, the rate of RRF decline estimated by generalized linear mixed models was significantly greater in patients with TA-Bic < 24 mEq/L compared with those with TA-Bic ≥ 24 mEq/L (-0.16 vs -0.11 mL/min/mo/1.73 m, P < 0.001).In this study, a clear association was found between low serum bicarbonate and loss of RRF in PD patients. Nevertheless, whether correction of metabolic acidosis for this indication provides additional protection for preserving RRF in these patients is unknown. Future interventional studies should more appropriately address this question.

Bicarbonate Therapy in End-Stage Renal Disease: Current Practice Trends and Implications

Management of metabolic acidosis covers the entire spectrum from oral bicarbonate therapy and dietary modifications in chronic kidney disease to delivery of high doses of bicarbonate-based dialysate during maintenance haemodialysis (MHD). Due to the gradual depletion of the body's buffers and rapid repletion during MHD, many potential problems arise as a result of our current treatment paradigms. Several studies have given rise to conflicting data about the adverse effects of our current practice patterns in MHD. In this review, we will describe the pathophysiology and consequences of metabolic acidosis and its therapy in CKD and ESRD, and discuss current evidence supporting a more individualized approach for bicarbonate therapy in MHD.

The effect of sodium bicarbonate on cytokine secretion in CKD patients with metabolic acidosis

The incidence of acidosis increases with the progression of chronic kidney disease (CKD). Correction of acidosis by sodium bicarbonate may slow CKD deterioration. Inflammation, which is common in CKD, may be related to acidosis. Whether the slower rate of GFR decline following the correction of acidosis is related to changes in inflammatory markers is unknown. The current study examined whether correcting CKD-acidosis affected inflammatory cytokines secretion. Thirteen patients with CKD 4-5 and acidosis were tested for cytokines secretion from peripheral-blood mononuclear cells at baseline and after one month of oral sodium bicarbonate. Following treatment with sodium bicarbonate there was no change in weight, blood pressure, serum creatinine, albumin, sodium, calcium, phosphate, PTH, hemoglobin and CRP. Serum urea decreased (134±10-116±8 mg/dl, P=0.002), potassium decreased (5.1±0.4-4.8±0.1 mequiv./l, P=0.064), pH increased (7.29±0.01-7.33±0.01, P=0.008), and serum bicarbonate increased (18.6±0.4 mequiv./l to 21.3±0.3 mequiv./l, P=0.001). The secretion of the anti-inflammatory cytokine IL-10 decreased (2.75±0.25 ng/ml to 2.29±0.21 ng/ml, P=0.041). There was no significant change in the secretion of the other pro-inflammatory and anti-inflammatory cytokines, including IL-1β, IL-2, IL-6, TNFα, IFNγ, IL-1ra. Thus, correcting acidosis in CKD with bicarbonate decreases IL-10 secretion. Its significance needs to be further investigated.

Effect of bicarbonate supplementation on renal function and nutritional indices in predialysis advanced chronic kidney disease

Current practice guidelines recommend alkali therapy in patients with chronic kidney disease (CKD) and metabolic acidosis to prevent complications. This study aims to investigate the effect of oral sodium bicarbonate supplementation on the progression of renal function and nutritional indices in patients with predialysis advanced CKD. Forty patients with predialysis stage 5 CKD(estimated glomerular filtration rate, eGFR <15mL/min per 1.73m²) and 40 patients with stage 4 CKD (eGFR 15 to 30mL/min per 1.73m²) who had a total CO₂ less than 22mEq/L were assigned into the bicarbonate treatment group or control group for 12 months. In stage 4 CKD, there were significant differences in the changes of eGFR during the study between the treatment group and the control group (-2.30±4.49 versus -6.58±6.32mL/min/1.73m², p<0.05). However, in stage 5 CKD, there were no significant differences in the change of eGFR during the study between the two groups (-2.10±2.06 versus -3.23±1.95mL/min/1.73 m²).There were no significant differences in the changes of nutritional indices such as albumin, prealbumin, transferrin, total lymphocyte count (TLC), and Ondodera's prognostic nutritional index (OPNI) during the study between the two groups. In stage 5 CKD, there were significant differences in the changes of TLC and OPNI between the two groups.

In conclusion, our results demonstrate that bicarbonate supplementation slows the rate of decline of renal function in stage 4 CKD and improves nutritional indices in stage 5 CKD. Alkali therapy in advanced CKD may have beneficial effect on renal function and malnutrition.

Optimization of Bone Health in Children before and after Renal Transplantation: Current Perspectives and Future Directions

The accrual of healthy bone during the critical period of childhood and adolescence sets the stage for lifelong skeletal health. However, in children with chronic kidney disease (CKD), disturbances in mineral metabolism and endocrine homeostasis begin early on, leading to alterations in bone turnover, mineralization, and volume, and impairing growth. Risk factors for CKD-mineral and bone disorder (CKD-MBD) include nutritional vitamin D deficiency, secondary hyperparathyroidism, increased fibroblast growth factor 23 (FGF-23), altered growth hormone and insulin-like growth factor-1 axis, delayed puberty, malnutrition, and metabolic acidosis. After kidney transplantation, nutritional vitamin D deficiency, persistent hyperparathyroidism, tertiary FGF-23 excess, hypophosphatemia, hypomagnesemia, immunosuppressive therapy, and alteration of sex hormones continue to impair bone health and growth. As function of the renal allograft declines over time, CKD-MBD associated changes are reactivated, further impairing bone health. Strategies to optimize bone health post-transplant include healthy diet, weight-bearing exercise, correction of vitamin D deficiency and acidosis, electrolyte abnormalities, steroid avoidance, and consideration of recombinant human growth hormone therapy. Other drug therapies have been used in adult transplant recipients, but there is insufficient evidence for use in the pediatric population at the present time. Future therapies to be explored include anti-FGF-23 antibodies, FGF-23 receptor blockers, and treatments targeting the colonic microbiota by reduction of generation of bacterial toxins and adsorption of toxic end products that affect bone mineralization.

Association between serum pregnancy-associated plasma protein-A and bicarbonate in hemodialysis patients

BACKGROUND

Acidosis is associated with protein-energy malnutrition, inflammation, and bone disease, and low bicarbonate levels have been implicated in higher mortality rates in chronic kidney disease. Recently, the concentration of serum pregnancy-associated plasma protein-A (PAPP-A) has become accepted as a prognostic marker in hemodialysis patients. This study determined the relationship between PAPP-A and bicarbonate levels in these patients.

METHODS

The study enrolled 65 hemodialysis patients (41 males, 24 females) and 26 control subjects (11 males, 15 females). Serum PAPP-A, intact parathormone (iPTH), calcium, phosphorus (P), and bicarbonate levels were measured. Correlations between PAPP-A and bicarbonate, iPTH, calcium, and phosphorus were evaluated.

RESULTS

Median PAPP-A levels were significantly higher in hemodialysis patients [15.1 (<0.03-158.8) ng/ml] than in control subjects [6.6 (<0.03-16.4) ng/ml] (P < 0.05). There were statistically significant correlations between serum PAPP-A and bicarbonate, iPTH, and P in hemodialysis patients but not in control subjects.

CONCLUSION

Elevation of serum PAPP-A has been found in hemodialysis patients and its significant correlation with bicarbonate suggests that it may be a prognostic factor.

Mineral and bone disorders in chronic kidney disease: new insights into mechanism and management

Chronic kidney disease (CKD) is now recognized as a major public health issue. One consequence of this condition is disturbance of mineral and bone homeostasis. Bone disease (renal osteodystrophy) as a consequence of CKD has long been recognized. However, it is now appreciated that the mineral and bone disturbances of CKD (and perhaps treatment of them) lead to vascular calcification, which is a cause of significant morbidity. In recognition of the widespread nature of the condition, the term CKD-mineral bone disorder (CKD-MBD) is now in general use to describe the biochemical, skeletal and vascular changes that occur in CKD. The pathogenesis of CKD-MBD is incompletely understood but has recently been redefined with the emergence of fibroblast growth factor 23 (FGF-23) as a major influence on control of vitamin D and parathyroid hormone. This review describes the classification of CKD and current understanding of the mechanisms underlying CKD-MBD (incorporating FGF-23). It describes and evaluates the means of identifying CKD-MBD in the clinical setting and the interventions available for treatment. It then reviews current clinical guidelines for the use of biochemical markers in clinical decision-making. In acknowledgement of the paucity of evidence upon which these guidelines are based, areas where clinical research might be directed in the future will be identified.

Short- and long-term effects of alkali therapy in chronic kidney disease: a systematic review

BACKGROUND

Clinical practice guidelines recommend alkali therapy in patients with non-dialysis-dependent chronic kidney disease (CKD) and metabolic acidosis to prevent complications from metabolic acidosis. We systematically reviewed the effect of sodium bicarbonate on benefits and harms in patients with CKD.

METHODS

We searched for randomized controlled trials in MEDLINE (through July 2011), Cochrane Central Register of Controlled Trials, ClinicalTrials.gov, and scientific abstracts. We included trials that compared sodium bicarbonate to standard-of-care therapy or placebo that reported on kidney-related outcomes. We performed random-effects model meta-analyses to compute net changes (for continuous variables) and risk ratios (for binary variables).

RESULTS

Two short-term (≤ 7 days) crossover trials and 4 long-term (≥ 2 months) parallel-design randomized controlled trials met eligibility (312 patients). All 6 trials prescribed sodium bicarbonate in the alkali-treated group. In the long-term studies, alkali therapy was associated with a net decrease in serum creatinine (-0.07 mg/dl, 95% CI -0.09, -0.05; p < 0.001; I(2) = 0), a net improvement in GFR (3.2 ml/min/1.73 m(2), 95% CI 1.6, 4.7; p < 0.001; I(2) = 0), and a lower incidence of dialysis initiation (risk ratio 0.21, 95% CI 0.08, 0.54; p = 0.001; I(2) = 0). No benefit was observed on the serum creatinine or GFR in short-term studies. Alkali therapy was not associated with a higher likelihood of initiating or escalating anti-hypertensive medications.

CONCLUSIONS

Alkali therapy is associated with an improvement in kidney function, which may afford a long-term benefit in slowing the progression of CKD. However, differences in study protocols and small sample sizes preclude definitive conclusions.

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

Recent studies suggest that correcting low serum bicarbonate levels may reduce the progression of kidney disease; however, few patients with chronic kidney disease have low serum bicarbonate. Therefore, we examined whether higher levels of serum bicarbonate within the normal range (20-30 mmol/l) were associated with better kidney outcomes in the African American Study of Kidney Disease and Hypertension (AASK) trial. At baseline and during follow-up of 1094 patients, the glomerular filtration rates (GFR) were measured by iothalamate clearances and events were adjudicated by the outcomes committee. Mean baseline serum bicarbonate, measured GFR, and proteinuria were 25.1 mmol/l, 46 ml/min per 1.73 m(2), and 326 mg/g of creatinine, respectively. Each 1 mmol/l increase in serum bicarbonate within the normal range was associated with reduced risk of death, dialysis, or GFR event and with dialysis or GFR event (hazard ratios of 0.942 and 0.932, respectively) in separate multivariable Cox regression models that included errors-in-variables calibration. Cubic spline regression showed that the lowest risk of GFR event or dialysis was found at serum bicarbonate levels near 28-30 mmol/l. Thus, our study suggests that serum bicarbonate is an independent predictor of CKD progression. Whether increasing serum bicarbonate into the high-normal range will improve kidney outcomes during interventional studies will need to be considered.

Relationship between bone mineral density and biochemical markers of bone turnover in hemodialysis patients

End-stage renal disease is closely associated with changes in bone and mineral metabolism. In recent times, osteoporosis has become important among hemodialysis (HD) patients. In this study, the investigators sought to evaluate the relationship between bone mineral density (BMD) and biochemical markers of bone turnover among HD patients. A total of 70 uremic patients on a maintenance HD program for at least 1 y were enrolled in the study. All patients were treated with conventional bicarbonated HD for 5 h through the use of low-flux hollow-fiber dialyzers. Bone densitometry was measured by dual energy x-ray absorptiometry in the lumbar spine (LS) and the femoral neck (FN). BMD was classified according to World Health Organization criteria on the basis of BMD T scores. Biochemical bone turnover markers such as calcium, phosphorus, ionized calcium, intact parathyroid hormone, alkaline phosphatase, plasma bicarbonate, blood pH, serum albumin, and hematocrit levels were measured before the HD session in the morning. Male patients (n=37; 52.9%; mean age, 46.2+/-17.0 y) were assigned to a single study group, and female patients (n=33; 47.1%; mean age, 44.0+/-13.1 y) to another. Mean duration of HD treatment was 33.7+/-28.5 mo in females and 33.0+/-26.0 mo in males. Among all patients, BMD T scores in the osteopenia/osteoporosis range were observed at the LS in 58 patients (82.8%) and at the FN in 45 patients (64.3%). According to BMD measurements in FN T score, 10% of patients (n=7) were osteoporotic, 54.3% (n=38), osteopenic, and 35.7% (n=25), normal. On the other hand, in LS T score, the results were 47.1% (n=33) osteoporotic, 35.7% (n=25), osteopenic, and 17.1% (n=12), normal. No statistically significant association was found in osteopenia/osteoporosis between sexes according to FN and LS T score (P=.542, P=.267, respectively). No significant relationship was noted between BMD and biochemical markers of bone turnover. A positive correlation was found between FN T scores of BMD and age (r=.413, P=.000). BMD T scores within the range of scores for osteopenia/osteoporosis were observed in 78.5% of patients at the LS and in 58.5% of patients at the FN. The investigators concluded that no correlation could be found between markers of bone turnover and bone mass measurements in both skeletal regions. LS T score results were worse than FN T score results. Elevated alkaline phosphastase levels combined with high intact parathyroid hormone levels are predictive of renal osteodystrophy but not of adynamic bone disease/osteoporosis.

Correction of chronic metabolic acidosis for chronic kidney disease patients

BACKGROUND

Metabolic acidosis is a feature of chronic kidney disease (CKD) due to the reduced capacity of the kidney to synthesise ammonia and excrete hydrogen ions. It has adverse consequences on protein and muscle metabolism, bone turnover and the development of renal osteodystrophy. Metabolic acidosis may be corrected by oral bicarbonate supplementation or in dialysis patients by increasing the bicarbonate concentration in dialysate fluid.

OBJECTIVES

To examine the benefits and harms of treating metabolic acidosis in patients with CKD, both prior to reaching end-stage renal disease (ESRD) or whilst on renal replacement therapy (RRT), with sodium bicarbonate or increasing the bicarbonate concentration of dialysate.

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library, issue 4 2005), Cochrane Renal Group's specialised register (October 2005), MEDLINE (1966 - October 2005) and EMBASE (1980 - October 2005).

SELECTION CRITERIA

Randomised controlled trials (RCTs), crossover RCTs and quasi-RCTs investigating the correction of chronic metabolic acidosis in adults or children with CKD.

DATA COLLECTION AND ANALYSIS

Outcomes were analysed using relative risk (RR) and weighted mean difference (MD) for continuous measures.

MAIN RESULTS

We identified three trials in adult dialysis patients (n = 117). There were insufficient data for most outcomes for meta-analysis. In all three trials acidosis improved in the intervention group though there was variation in achieved bicarbonate level. There was no evidence of effect on blood pressure or sodium levels. Some measures of nutritional status/protein metabolism (e.g. SGA, NP NA) were significantly improved by correction in the one trial that looked in these in detail. There was heterogeneity of the effect on serum albumin in two trials. Serum PTH fell significantly in the two trials that estimated this, there was no significant effect on calcium or phosphate though both fell after correction. Complex bone markers were assessed in one study, with some evidence for a reduction in bone turnover in those with initial high bone turnover and an increase in low turnover patients. The studies were underpowered to assess clinical outcomes, in the one study that did there was some evidence for a reduction in hospitalisation after correction.

AUTHORS' CONCLUSIONS

The evidence for the benefits and risks of correcting metabolic acidosis is very limited with no RCTs in pre-ESRD patients, none in children, and only three small trials in dialysis patients. These trials suggest there may be some beneficial effects on both protein and bone metabolism but the trials were underpowered to provide robust evidence.