Correcting Acidosis during Hemodialysis: Current Limitations and a Potential Solution

Change in plasma electrolyte concentrations during hemodialysis following a controlled step-up in dialysate bicarbonate concentration

BACKGROUND

The concentration of bicarbonate in dialysis fluid (Dbic) that regulates acid-base balance in dialyzed patients is individually adjusted and may be modified during a hemodialysis session. We evaluated the impact of modifications of Dbic on plasma electrolytes.

METHODS

Two midweek hemodialysis sessions were monitored in 25 anuric, prevalent hemodialysis patients (67.9 ± 9.3 years old, 32% females). During the first session (treatment A) Dbic was constant at 33.6 ± 1.7 mmol/L, while for the second week (treatment B) it was on average 30.8 ± 2.3 mmol/L for the initial 2 h and 34.0 ± 2.5 mmol/L for the last 2 h.

RESULTS

During treatments A and B plasma bicarbonate (Pbic) increased during the sessions and was lower for treatment B than A at 60 and 120 min of dialysis. Plasma chloride decreased during treatments A and B and was significantly higher at 60 and 120 min of dialysis in treatment B than in treatment A. An increase of plasma calcium was observed during both treatments and it was higher for treatment B than A at 60 and 120 min. A similar profile of plasma sodium and potassium was observed during treatments A and B. The difference in Pbic correlated positively, whereas the differences in plasma chloride and calcium correlated negatively, with the difference in Dbic between treatments B and A.

CONCLUSION

Modifications of dialysate bicarbonate may influence the concentrations of some other electrolytes in plasma; for each percent of Dbic increase one may expect -0.27 and -0.16% change in plasma chloride and calcium, respectively.

Oral Sodium Bicarbonate vs. Use of Higher Dialysate Bicarbonate in Hemodialysis Patients With Metabolic Acidosis: A Randomized Controlled Trial

INTRODUCTION

The optimal strategy for correcting metabolic acidosis and maintaining acid-base balance in hemodialysis patients remains unclear. This study aimed to evaluate and compare the effects of oral bicarbonate administration vs. increased dialysate bicarbonate concentration on predialysis serum bicarbonate levels in hemodialysis patients with metabolic acidosis.

METHODS

This was a single-center, open-label, randomized controlled trial. Adult hemodialysis patients with metabolic acidosis (serum bicarbonate < 22 mmol/L) were randomly assigned in a 1:1:1 ratio to one of three treatment groups for 16 weeks: (1) standard dialysate (32 mM bicarbonate plus 3 mM acetate), (2) increased dialysate bicarbonate (34 mM bicarbonate plus 3 mM acetate), or (3) standard dialysate with daily oral sodium bicarbonate supplementation (0.3-0.5 mmol/kg). Of the 75 eligible participants, 66 completed the study. The primary outcome was the difference in predialysis serum bicarbonate levels between the groups at 16 weeks.

RESULTS

Baseline predialysis serum bicarbonate levels averaged approximately 19.5 mmol/L across all three groups. At 16 weeks, there was no statistically significant difference in predialysis serum bicarbonate levels among the groups (p = 0.701). The mean levels were 20.1 (SD 2.16) mmol/L in the standard dialysate group, 20.5 (SD 2.04) mmol/L in the increased dialysate bicarbonate group, and 20.8 (SD 2.61) mmol/L in the oral supplementation group. Compared to baseline, predialysis bicarbonate levels significantly increased within the increased dialysate bicarbonate group (p = 0.010) and the oral supplementation group (p = 0.021), but not in the control (standard dialysate, no oral supplementation) group.

CONCLUSION

Oral or dialytic bicarbonate supplementation at the doses used in this study demonstrated equivalent effects on predialysis serum bicarbonate concentrations in acidotic hemodialysis patients. However, the amount of supplemental bicarbonate administered via either route was insufficient to achieve the target correction of acidosis (e.g., predialysis serum bicarbonate ≥ 22 mmol/L).

Hemodialysis Procedures for Stable Incident and Prevalent Patients Optimize Hemodynamic Stability, Dialysis Dose, Electrolytes, and Fluid Balance

The demographic profile of patients transitioning from chronic kidney disease to kidney replacement therapy is changing, with a higher prevalence of aging patients with multiple comorbidities such as diabetes mellitus and heart failure. Cardiovascular disease remains the leading cause of mortality in this population, exacerbated by the cardiovascular stress imposed by the HD procedure. The first year after transitioning to hemodialysis is associated with increased risks of hospitalization and mortality, particularly within the first 90-120 days, with greater vulnerability observed among the elderly. Based on data from clinics in Fresenius Medical Care Europe, Middle East, and Africa NephroCare, this review aims to optimize hemodialysis procedures to reduce mortality risk in stable incident and prevalent patients. It addresses critical aspects such as treatment duration, frequency, choice of dialysis membrane, dialysate composition, blood and dialysate flow rates, electrolyte composition, temperature control, target weight management, dialysis adequacy, and additional protocols, with a focus on mitigating prevalent intradialytic complications, particularly intradialytic hypotension prevention.

Effect of time-dependent dialysate bicarbonate concentrations on acid-base and uremic solute kinetics during hemodialysis treatments

Recent studies have suggested benefits for time-dependent dialysate bicarbonate concentrations (Dbic) during hemodialysis (HD). In this clinical trial, we compared for the first time in the same HD patients the effects of time-dependent changes with constant Dbic on acid-base and uremic solute kinetics. Blood acid-base and uremic solute concentration were measured in twenty chronic HD patients during 4-h treatments with A) constant Dbic of 35 mmol/L; B) Dbic of 35 mmol/L then 30 mmol/L; and C) Dbic of 30 mmol/L then 35 mmol/L (change of Dbic after two hours during Treatments B and C). Arterial blood samples were obtained predialysis, every hour during HD and one hour after HD, during second and third treatments of the week with each Dbic concentration profile. Blood bicarbonate concentration (blood [HCO3]) during Treatment C was lower only during the first three HD hours than in Treatment A. Overall blood [HCO3] was reduced during Treatment B in comparison to Treatment A at each time points. We conclude that a single change Dbic in the middle of HD can alter the rate of change in blood [HCO3] and pH during HD; time-dependent Dbic had no influence on uremic solute kinetics.

Mathematical modelling of bicarbonate supplementation and acid-base chemistry in kidney failure patients on hemodialysis

Acid-base regulation by the kidneys is largely missing in end-stage renal disease patients undergoing hemodialysis (HD). Bicarbonate is added to the dialysis fluid during HD to replenish the buffers in the body and neutralize interdialytic acid accumulation. Predicting HD outcomes with mathematical models can help select the optimal patient-specific dialysate composition, but the kinetics of bicarbonate are difficult to quantify, because of the many factors involved in the regulation of the bicarbonate buffer in bodily fluids. We implemented a mathematical model of dissolved CO2 and bicarbonate transport that describes the changes in acid-base equilibrium induced by HD to assess the kinetics of bicarbonate, dissolved CO2, and other buffers not only in plasma but also in erythrocytes, interstitial fluid, and tissue cells; the model also includes respiratory control over the partial pressures of CO2 and oxygen. Clinical data were used to fit the model and identify missing parameters used in theoretical simulations. Our results demonstrate the feasibility of the model in describing the changes to acid-base homeostasis typical of HD, and highlight the importance of respiratory regulation during HD.

Acid-base balance in hemodialysis patients in everyday practice

Introduction

Abnormalities in blood bicarbonates (HCO₃^–) concentration are a common finding in patients with chronic kidney disease, especially at the end-stage renal failure. Initiating of hemodialysis does not completely solve this problem. The recommendations only formulate the target concentration of ≥22 mmol/L before hemodialysis but do not guide how to achieve it. The aim of the study was to assess the acid–base balance in everyday practice, the effect of hemodialysis session and possible correlations with clinical and biochemical parameters in stable hemodialysis patients.

Material and methods

We enrolled 75 stable hemodialysis patients (mean age 65.5 years, 34 women), from a single Department of Nephrology. We assessed blood pressure, and acid–base balance parameters before and after mid-week hemodialysis session.

Results

We found significant differences in pH, HCO₃^– pCO₂, lactate before and after HD session in whole group (p < 0.001; p < 0.001; p < 0.001; p = 0.001, respectively). Buffer bicarbonate concentration had only statistically significant effect on the bicarbonate concentration after dialysis (p < 0.001). Both pre-HD acid–base parameters and post-HD pH were independent from buffer bicarbonate content. We observed significant inverse correlations between change in the serum bicarbonates and only two parameters: pH and HCO₃^– before hemodialysis (p = 0.013; p < 0.001, respectively).

Conclusions

Despite the improvement in hemodialysis techniques, acid–base balance still remains a challenge. The individual selection of bicarbonate in bath, based on previous single tests, does not improve permanently the acid–base balance in the population of hemodialysis patients. New guidelines how to correct acid–base disorders in hemodialysis patients are needed to have less ‘acidotic’ patients before hemodialysis and less ‘alkalotic’ patients after the session.

Replenishing Alkali During Hemodialysis: Physiology-Based Approaches

The acid-base goal of intermittent hemodialysis is to replenish buffers consumed by endogenous acid production and expansion acidosis in the period between treatments. The amount of bicarbonate needed to achieve this goal has traditionally been determined empirically with a goal of obtaining a reasonable subsequent predialysis blood bicarbonate concentration ([HCO₃^-]). This approach has led to very disparate hemodialysis prescriptions around the world. The bath [HCO₃^-] usually chosen in the United States and Europe causes a rapid increase in blood [HCO₃^-] in the first 1-2 hours of treatment, with little change thereafter. New studies show that this abrupt increase in blood [HCO₃^-] elicits a buffer response that removes more bicarbonate from the extracellular compartment than is added in the second half of treatment, a futile and unnecessary event. We propose that changes in dialysis prescription be studied in an attempt to moderate the initial rate of increase in blood [HCO₃^-] and the magnitude of the body buffer response. These new approaches include either a much lower bath [HCO₃^-] coupled with an increase in the bath acetate concentration or a stepwise increase in the bath [HCO₃^-] during treatment. In a subset of patients with low endogenous acid production, we propose reducing the bath [HCO₃^-] as the sole intervention.

Choices in hemodialysis therapies: variants, personalized therapy and application of evidence-based medicine

The extent of removal of the uremic toxins in hemodialysis (HD) therapies depends primarily on the dialysis membrane characteristics and the solute transport mechanisms involved. While designation of ‘flux’ of membranes as well toxicity of compounds that need to be targeted for removal remain unresolved issues, the relative role, efficiency and utilization of solute removal principles to optimize HD treatment are better delineated. Through the combination and intensity of diffusive and convective removal forces, levels of concentrations of a broad spectrum of uremic toxins can be lowered significantly and successfully. Extended clinical experience as well as data from several clinical trials attest to the benefits of convection-based HD treatment modalities. However, the mode of delivery of HD can further enhance the effectiveness of therapies. Other than treatment time, frequency and location that offer clinical benefits and increase patient well-being, treatment- and patient-specific criteria may be tailored for the therapy delivered: electrolytic composition, dialysate buffer and concentration and choice of anticoagulating agent are crucial for dialysis tolerance and efficacy. Evidence-based medicine (EBM) relies on three tenets, i.e. clinical expertise (i.e. doctor), patient-centered values (i.e. patient) and relevant scientific evidence (i.e. science), that have deviated from their initial aim and summarized to scientific evidence, leading to tyranny of randomized controlled trials. One must recognize that practice patterns as shown by Dialysis Outcomes and Practice Patterns Study and personalization of HD care are the main driving force for improving outcomes. Based on a combination of the three pillars of EBM, and particularly on bedside patient–clinician interaction, we summarize what we have learned over the last 6 decades in terms of best practices to improve outcomes in HD patients. Management of initiation of dialysis, vascular access, preservation of kidney function, selection of biocompatible dialysers and use of dialysis fluids of high microbiological purity to restrict inflammation are just some of the approaches where clinical experience is vital in the absence of definitive scientific evidence. Further, HD adequacy needs to be considered as a broad and multitarget approach covering not just the dose of dialysis provided, but meeting individual patient needs (e.g. fluid volume, acid–base, blood pressure, bone disease metabolism control) through regular assessment—and adjustment—of a series of indicators of treatment efficiency. Finally, in whichever way new technologies (i.e. artificial intelligence, connected health) are embraced in the future to improve the delivery of dialysis, the human dimension of the patient–doctor interaction is irreplaceable. Kidney medicine should remain ‘an art’ and will never be just ‘a science’.

Hemodynamic and Laboratory Changes during Incremental Transition from Twice to Thrice-Weekly Hemodialysis

OBJECTIVE

Incremental hemodialysis (HD) is a strategy utilized to gradually intensify dialysis among patients with incident end-stage renal disease. However, there are scarce data about which patients' clinic status changes by increasing treatment frequency.

METHODS

We retrospectively examined statistically de-identified data from 569 patients who successfully transitioned from twice- to thrice-weekly HD (2007-2011) and compared the differences in monthly-averaged values of hemodynamic and laboratory indices during the 3 months before and after the transition with the values at 1 month prior to transition serving as the reference.

RESULTS

At 3 months after transitioning from twice- to thrice-weekly HD, ultrafiltration volume decreased by 0.5 (95% CI 0.3-0.6) L/session among 189 patients (33%) with weekly interdialytic weight gain (IDWG) ≥5.4 kg/week, and increased by 0.4 (95% CI 0.3-0.5) L/session among 186 patients (33%) with weekly IDWG <3.3 kg/week. Weekly IDWG consistently increased after the transition irrespective of baseline values (1.7 [95% CI 1.5-1.9] kg/week). Pre-HD systolic blood pressure (SBP) decreased by 12 (95% CI 9-14) mm Hg among 177 patients (31%) with baseline pre-HD SBP ≥160 mm Hg, which coincided with a decreasing trend in post-HD body weight (1.3 [95% CI 0.8-1.7] kg).

DISCUSSION

In conclusion, patients who increased HD frequency from twice to thrice weekly treatment experienced increased weekly IDWG and better pre-HD SBP control with lower post-HD body weight.

Acid-base alterations in ESRD and effects of hemodialysis

Acid-base alterations in patients with kidney failure and on hemodialysis (HD) treatment contribute to (1) intradialytic hypercapnia and hypoxia, (2) hemodynamic instability and cardiac arrhythmia, (3) systemic inflammation, and (4) a number of associated electrolyte alterations including potentiating effects of hypokalemia, hypocalcemia and, chronically, soft-tissue and vascular calcification, imparting poor prognosis and mortality. This paper discusses acid-base regulation and pathogenesis of dysregulation in patients with kidney failure. Major organ and systemic effects of acid-base perturbations with a specific focus on kidney failure patients on HD are emphasized, and potential mitigating strategies proposed. The high rate of HD-related complications, specifically those that can be accounted for by rapid and steep acid-base perturbations imposed by HD treatment, attests to the pressing need for investigations to establish a better dialysis regimen.

Bicarbonate Balance and Prescription in ESRD

The optimal approach to managing acid-base balance is less well defined for patients receiving hemodialysis than for those receiving peritoneal dialysis. Interventional studies in hemodialysis have been limited and inconsistent in their findings, whereas more compelling data are available from interventional studies in peritoneal dialysis. Both high and low serum bicarbonate levels associate with an increased risk of mortality in patients receiving hemodialysis, but high values are a marker for poor nutrition and comorbidity and are often highly variable from month to month. Measurement of pH would likely provide useful additional data. Concern has arisen regarding high-bicarbonate dialysate and dialysis-induced alkalemia, but whether these truly cause harm remains to be determined. The available evidence is insufficient for determining the optimal target for therapy at this time.

The choice of dialysate bicarbonate: do different concentrations make a difference?

Metabolic acidosis is a common complication of chronic kidney disease; it is typically caused by the accumulation of sulfate, phosphorus, and organic anions. Metabolic acidosis is correlated with several adverse outcomes, such as morbidity, hospitalization, and mortality. Thus, correction of metabolic acidosis is fundamental for the adequate management of many systemic complications of chronic kidney disease. In patients undergoing hemodialysis, acid-base homeostasis depends on many factors including the following: net acid production, amount of alkali given by the dialysate bath, duration of the interdialytic period, and residual diuresis, if any. Recent literature data suggest that the development of metabolic alkalosis after dialysis may contribute to adverse clinical outcomes. Our review is focused on the potential effects of different dialysate bicarbonate concentrations on hard outcomes such as mortality. Unfortunately, no randomized studies exist about this issue. Acid-base equilibrium is a complex and vital system whose regulation is impaired in chronic kidney disease. We await further studies to assess the extent to which acid-base status is a major determinant of overall survival in patients undergoing hemodialysis. For the present, the clinician should understand that target values for predialysis serum bicarbonate concentration have been established primarily based on observational studies and expert opinion. Based on this, we should keep the predialysis serum bicarbonate level at least at 22 mmol/l. Furthermore, a specific focus should be addressed by the attending nephrologist to the clinical and nutritional status of the major outliers on both the acid and alkaline sides of the curve.