Varying Dialysate Bicarbonate Concentrations in Maintenance Hemodialysis Patients Affect Post-dialysis Alkalosis but not Pre-dialysis Acidosis

Association Between the Dialysate Bicarbonate and the Pre-dialysis Serum Bicarbonate Concentration in Maintenance Hemodialysis: A Retrospective Cohort Study

Background

It is unclear whether the use of higher dialysate bicarbonate concentrations is associated with clinically relevant changes in the pre-dialysis serum bicarbonate concentration.

Objective

The objective is to examine the association between the dialysate bicarbonate prescription and the pre-dialysis serum bicarbonate concentration.

Design

This is a retrospective cohort study.

Setting

The study was performed using linked administrative health care databases in Ontario, Canada.

Patients

Prevalent adults receiving maintenance in-center hemodialysis as of April 1, 2020 (n = 5414) were included.

Measurements

Patients were grouped into the following dialysate bicarbonate categories at the dialysis center-level: individualized (adjustment based on pre-dialysis serum bicarbonate concentration) or standardized (>90% of patients received the same dialysate bicarbonate concentration). The standardized category was stratified by concentration: 35, 36 to 37, and ≥38 mmol/L. The primary outcome was the mean outpatient pre-dialysis serum bicarbonate concentration at the patient level.

Methods

We examined the association between dialysate bicarbonate category and pre-dialysis serum bicarbonate using an adjusted linear mixed model.

Results

All dialysate bicarbonate categories had a mean pre-dialysis serum bicarbonate concentration within the normal range. In the individualized category, 91% achieved a pre-dialysis serum bicarbonate ≥22 mmol/L, compared to 87% in the standardized category. Patients in the standardized category tended to have a serum bicarbonate that was 0.25 (95% confidence interval [CI] = -0.93, 0.43) mmol/L lower than patients in the individualized category. Relative to patients in the 35 mmol/L category, patients in the 36 to 37 and ≥38 mmol/L categories tended to have a serum bicarbonate that was 0.70 (95% CI = -0.30, 1.70) mmol/L and 0.87 (95% CI = 0.14, 1.60) mmol/L higher, respectively. There was no effect modification by age, sex, or history of chronic lung disease.

Limitations

We could not directly confirm that all laboratory measurements were pre-dialysis. Data on prescribed dialysate bicarbonate concentrations for individual dialysis sessions were not available, which may have led to some misclassification, and adherence to a practice of individualization could not be measured. Residual confounding is possible.

Conclusions

We found no significant difference in the pre-dialysis serum bicarbonate concentration irrespective of whether an individualized or standardized dialysate bicarbonate was used. Dialysate bicarbonate concentrations ≥38 mmol/L (vs 35 mmol/L) may increase the pre-dialysis serum bicarbonate concentration by 0.9 mmol/L.

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.

A four-stream method for providing variable dialysis fluid bicarbonate concentrations for bicarbonate-based dialysis fluid delivery systems

BACKGROUND

Hemodialysis corrects metabolic acidosis by transferring bicarbonate or bicarbonate equivalents across the dialysis membrane from the dialysis fluid to the plasma. With the conventional three-stream bicarbonate-based dialysis fluid delivery system, a change in the bicarbonate concentration results in changes in the other electrolytes. In practice, the dialysis machine draws either a little less or more from the bicarbonate concentrate and a little more or less from the acid concentrate, respectively in a three-stream delivery system. The result not only changes the bicarbonate concentration of the final dialysis fluid but also causes a minor change in the other ingredients.

METHODS

We propose a four-stream bicarbonate-based dialysis fluid delivery system consisting of an acid concentrate, a base concentrate, a product water, and a new sodium chloride concentrate.

RESULTS

By adjusting the flow rate ratio between the sodium chloride and sodium bicarbonate concentrates, one can achieve the desired bicarbonate concentration in the dialysis fluid without changing the concentration of sodium or ingredients in the acid concentrate. The chloride concentration mirrors the change in bicarbonate but in the opposite direction.

CONCLUSION

A four-stream, bicarbonate-based dialysis fluid delivery system allows the bicarbonate concentration to be changed without changing the other constituents of the final dialysis fluid.

Case in Point: Correction of Dialysis-Induced Metabolic Alkalosis

Normal saline solution infusion with concurrent removal by ultrafiltration successfully corrected pretreatment metabolic alkalosis when other measures were inadequate for a patient on dialysis.

Acid-Base and Electrolyte Managements in Chronic Kidney Disease and End-Stage Renal Disease: Case-Based Discussion

Acid-base and electrolyte alterations are common in patients with chronic kidney disease (CKD) and end-stage kidney failure (ESRD). The alterations become more complex as CKD advances to ESRD, leading to morbidity and mortality. Three cases are presented illustrating some key prototypic features in CKD and ESRD. Each is accompanied by discussion of pathophysiology, diagnosis, and treatment options. Newer investigational results are integrated into the existing body of knowledge. Although rigorous assessment of various dialysis prescriptions is scanty, in its current state, instituting a well thought-out, multi-pronged management plan to minimize CKD/ESRD and dialysis-related electrolyte and acid-base disruptions is appropriate. There is a pressing need for prospective interventional trials in the future.

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.

Predialysis and Postdialysis pH and Bicarbonate and Risk of All-Cause and Cardiovascular Mortality in Long-term Hemodialysis Patients

BACKGROUND

To date, very few studies have been carried out on the associations of pre- and postdialysis acid-base parameters with mortality in hemodialysis patients.

STUDY DESIGN

An observational study including cross-sectional and 1-year analyses.

SETTING & PARTICIPANTS

Data from the renal registry of the Japanese Society of Dialysis Therapy (2008-2009), including 15,132 dialysis patients 16 years or older.

PREDICTOR

Predialysis pH<7.30, 7.30 to 7.34 (reference), 7.35 to 7.39, or ≥7.40 (1,550, 4,802, 6,023, and 2,757 patients, respectively); predialysis bicarbonate level < 18.0, 18.0 to 21.9 (reference), 22.0 to 25.9, or ≥26.0 mEq/L (2,724, 7,851, 4,023, and 534 patients, respectively); postdialysis pH<7.40, 7.40 to 7.44, 7.45 to 7.49 (reference), or ≥7.50 (2,114, 5,331, 4,975, and 2,712 patients, respectively); and postdialysis bicarbonate level < 24.0, 24.0 to 25.9, 26.0 to 27.9 (reference), or ≥28.0 mEq/L (5,087, 4,330, 3,451, and 2,264 patients, respectively).

OUTCOMES

All-cause and cardiovascular (CV) mortality during the 1-year follow-up.

MEASUREMENTS

HRs were estimated using unadjusted models and models adjusted for age, sex, dialysis vintage, history of CV disease, diabetes, weight gain ratio, body mass index, calcium-phosphorus product, serum albumin level, serum total cholesterol level, blood hemoglobin level, single-pool Kt/V, and normalized protein catabolic rate.

RESULTS

Of 15,132 patients, during follow-up, 1,042 died of all causes, including 408 CV deaths. In the adjusted analysis for all-cause mortality, HRs compared to the reference group were significantly higher in patients with predialysis pH≥7.40 (HR, 1.36; 95% CI, 1.13-1.65) and postdialysis pH<7.40 (HR, 1.22; 95% CI, 1.00-1.49). Predialysis pH≥7.40 was also associated with higher risk of CV mortality (HR, 1.34; 95% CI, 1.01-1.79). No association of pre- or postdialysis bicarbonate level with all-cause and CV mortality was observed.

LIMITATIONS

Single measurements of acid-base parameters, short duration of follow-up, small number of CV deaths.

CONCLUSIONS

Predialysis pH≥7.40 was associated with significantly elevated risk of all-cause and CV mortality. However, pre- and postdialysis bicarbonate levels were not associated with all-cause and CV mortality. Predialysis pH may be the most appropriate reference for accurate correction of metabolic acidosis in dialysis patients.

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.

Differential effects of phosphate binders on pre-dialysis serum bicarbonate in end-stage kidney disease patients on maintenance haemodialysis

Background

Phosphate binders’ constituents have alkalotic or acidotic properties and may contribute to acid base balance in haemodialysis patients. This study aimed to investigate the differential effects of phosphate binders on pre-dialysis serum bicarbonate in End Stage Kidney Disease patients on maintenance haemodialysis.

Methods

Stable out-patients having satellite haemodialysis for at least 3 months were retrospectively studied for 18 months, excluding those with other medical causes for metabolic acidosis. Blood results were censored for inpatient episodes, at the time of death, renal transplant or dialysis modality change. Multivariable multilevel mixed-effects linear regression was used and five groups of phosphate binders were compared: Group A(Calcium (Ca) and/or Aluminium (Al) binders); B(Sevelamer hydrochloride (SH) alone); C(lanthanum carbonate (LC) alone); D(SH and Ca/Al), E(LC and Ca/Al).

Results

Of 320 patients, 292 were eligible for analysis with a mean follow-up of 15.54 (standard deviation, SD 3.98) months. Similar mean pre-dialysis serum levels of bicarbonate were observed at all 6 month-interval analyses. At 18^th months, observed mean serum bicarbonate levels in mmol/L were Group B: 21.58 (SD 2.82, P<0.001), C: 23.29 (SD 2.80, P=0.02), D: 21.56 (SD 3.00, P<0.001), and E: 21.29 (SD 3.62, P=0.92) compared with Group A: 22.98 (SD 2.77). Mean serum bicarbonate was related to total SH dose in mmol/L: 22.34 (SD 2.56) for SH <2.5 g/day, 21.61 (SD 2.62) for SH 2.5-4.8 g/day, 21.04 (SD 3.31) for SH >4.8 g/day compared with 22.85 (SD 2.91) for non-users; P-trend<0.001.

Conclusions

Phosphate binders’ constituents may contribute to/protect against a predisposition to pre-dialysis metabolic acidosis. This may be dose dependant in patients taking Sevelamer Hydrochloride.