Serum Potassium and the Long Interdialytic Interval: Minding the Gap

Potassium homeostasis and therapeutic intervention with sodium zirconium cyclosilicate: A model-informed drug development case study

Potassium (K+ ) is the main intracellular cation in the body. Elevated K+ levels (hyperkalemia) increase the risk of life-threatening arrhythmias and sudden cardiac death. However, the details of K+ homeostasis and the effects of orally administered K+ binders, such as sodium zirconium cyclosilicate (SZC), on K+ redistribution and excretion in patients remain incompletely understood. We built a fit-for-purpose systems pharmacology model to describe K+ homeostasis in hyperkalemic subjects and capture serum K+ (sK+ ) dynamics in response to acute and chronic administration of SZC. The resulting model describes K+ distribution in the gastrointestinal (GI) tract, blood, and extracellular and intracellular spaces of tissue, renal clearance of K+ , and K+ -SZC binding and excretion in the GI tract. The model, which was fit to time-course sK+ data for individual patients from two clinical trials, accounts for bolus delivery of K+ in meals and oral doses of SZC. The virtual population of patients derived from fitting the model to these trials was then modified to predict the SZC dose-response and inform clinical trial design in two new applications: emergency lowering of sK+ in severe hyperkalemia and prevention of hyperkalemia between dialysis sessions in patients with end-stage chronic kidney disease. In both cases, the model provided novel and useful insight that was borne out by the now completed clinical trials, providing a concrete case study of fit-for-purpose, model-informed drug development after initial approval of a drug.

Racial Disparities in End-Stage Kidney Disease Outcomes among Asians and Native Hawaiians and Other Pacific Islanders across Geographic Residence

INTRODUCTION

While Asian and Native Hawaiian and other Pacific Islander (NHOPI) patients have a high prevalence of kidney disease risk factors, there are sparse data examining their end-stage kidney disease (ESKD) outcomes. As Hawaii has high representation of Asian and NHOPI individuals, we compared their ESKD outcomes based on residence in the mainland USA versus Hawaii/Pacific Islands (PIs).

MATERIALS AND METHODS

Using United States Renal Data System data, we examined the impact of geographic residence in the mainland versus Hawaii/PIs on race-mortality associations among incident ESKD patients transitioning to dialysis over January 1, 2000-December 31, 2016 using Cox regression. We examined likelihood of post-dialysis kidney transplantation using Cox models and cumulative incidence curves.

RESULTS

Compared with White patients in the mainland, Asian and NHOPI patients in the mainland had lower mortality: adjusted HRs (95% CIs) 0.67 (0.66-0.67) and 0.72 (0.70-0.73), respectively. When examining Asian and NHOPI patients in Hawaii/PIs, survival benefit was attenuated in Asian and diminished to the null in NHOPI patients (ref: mainland White patients). Cumulative incidence curves comparing Asian, NHOPI, and White patients showed Asian and NHOPI patients in the mainland had the highest likelihood of transplantation, whereas NHOPI and Asian patients in Hawaii/PIs had the lowest likelihood.

CONCLUSION

In the mainland, Asian and NHOPI patients had lower mortality versus White patients, whereas in Hawaii/PIs, this survival benefit was diminished in Asian and mitigated in NHOPI patients. NHOPI and Asian patients in Hawaii/PIs had less transplantation versus those in the mainland. Further research is needed to uncover factors contributing to differential ESKD outcomes among Asian and NHOPI patients across geographic residence.

Digital health technology to support care and improve outcomes of chronic kidney disease patients: as a case illustration, the Withings toolkit health sensing tools

Cardiovascular disease (CVD) is a major burden in dialysis-dependent chronic kidney disease (CKD5D) patients. Several factors contribute to this vulnerability including traditional risk factors such as age, gender, life style and comorbidities, and non-traditional ones as part of dialysis-induced systemic stress. In this context, it appears of utmost importance to bring a closer attention to CVD monitoring in caring for CKD5D patients to ensure early and appropriate intervention for improving their outcomes. Interestingly, new home-used, self-operated, connected medical devices offer convenient and new tools for monitoring in a fully automated and ambulatory mode CKD5D patients during the interdialytic period. Sensoring devices are installed with WiFi or Bluetooth. Some devices are also available in a cellular version such as the Withings Remote Patient Monitoring (RPM) solution. These devices analyze the data and upload the results to Withings HDS (Hybrid data security) platform servers. Data visualization can be viewed by the patient using the Withings Health Mate application on a smartphone, or with a web interface. Health Care Professionals (HCP) can also visualize patient data via the Withings web-based RPM interface. In this narrative essay, we analyze the clinical potential of pervasive wearable sensors for monitoring ambulatory dialysis patients and provide an assessment of such toolkit digital medical health devices currently available on the market. These devices offer a fully automated, unobtrusive and remote monitoring of main vital functions in ambulatory subjects. These unique features provide a multidimensional assessment of ambulatory CKD5D patients covering most physiologic functionalities, detecting unexpected disorders (i.e., volume overload, arrhythmias, sleep disorders) and allowing physicians to judge patient's response to treatment and recommendations. In the future, the wider availability of such pervasive health sensing and digital technology to monitor patients at an affordable cost price will improve the personalized management of CKD5D patients, so potentially resulting in improvements in patient quality of life and survival.

Associations of Serum and Dialysate Potassium Concentrations With Incident Atrial Fibrillation in a Cohort Study of Older US Persons Initiating Hemodialysis for Kidney Failure

Introduction

Atrial fibrillation (AF) disproportionally affects persons on maintenance hemodialysis (HD). Associations of serum and dialysate potassium concentrations [K⁺] with AF incidence are poorly understood.

Methods

We conducted a cohort study using Medicare claims merged with clinical data from a dialysis provider to determine whether serum-[K⁺] and/or dialysate-[K⁺] independently associated with AF incidence. Persons insured by fee-for-service Medicare aged ≥67 years at dialysis initiation and free from diagnosed AF prior to day 120 of dialysis were eligible. Serum-[K⁺] and dialysate-[K⁺] were assessed in 30-day intervals and patients were followed-up with for AF incidence in subsequent 30-day intervals.

Results

During 2006 to 2011, 15,190 persons (mean age = 76.3 years) initiating HD had no prior AF diagnosis. Mean serum-[K⁺] was 4.5 mEq/l; dialysate-[K⁺] was 3 mEq/l in 34% and 2 mEq/l in 52% of patients. Followed-up over 21,907 person-years, 2869 persons had incident AF (incidence/100 person-years, 13.1 [95% confidence interval [CI], 12.6-13.6]). The multivariable-adjusted association of serum-[K⁺] with incident AF was J-shaped as follows: relative to a serum-[K⁺] of 4.5 mEq/l, lower serum-[K⁺] associated with increased AF risk, whereas confidence bands for higher serum-[K⁺] indicated no association. Dialysis against a dialysate-[K+] of 3 mEq/l versus 2 mEq/l independently associated with a 14% (95% CI, 5%-24%) lower incidence of AF. No effect modification between serum-[K⁺] and dialysate-[K⁺] was detected (P = 0.34).

Conclusion

Lower serum-[K⁺] was independently associated with incident AF whereas elevated serum-[K+] was not. The findings support adoption of dialysate solutions with a dialysate-[K⁺] of 3 mEq/l, regardless of patients' serum-[K+], and elimination of lower dialysate-[K+] solutions from practice. Clinical trials randomizing patients to different dialysate-[K⁺] are warranted to establish causality.

Association Between Preoperative Hemodialysis Timing and Postoperative Mortality in Patients With End-stage Kidney Disease

Importance

For patients with end-stage kidney disease treated with hemodialysis, the optimal timing of hemodialysis prior to elective surgical procedures is unknown.

Objective

To assess whether a longer interval between hemodialysis and subsequent surgery is associated with higher postoperative mortality in patients with end-stage kidney disease treated with hemodialysis.

Design, Setting, and Participants

Retrospective cohort study of 1 147 846 procedures among 346 828 Medicare beneficiaries with end-stage kidney disease treated with hemodialysis who underwent surgical procedures between January 1, 2011, and September 30, 2018. Follow-up ended on December 31, 2018.

Exposures

One-, two-, or three-day intervals between the most recent hemodialysis treatment and the surgical procedure. Hemodialysis on the day of the surgical procedure vs no hemodialysis on the day of the surgical procedure.

Main Outcomes and Measures

The primary outcome was 90-day postoperative mortality. The relationship between the dialysis-to-procedure interval and the primary outcome was modeled using a Cox proportional hazards model.

Results

Of the 1 147 846 surgical procedures among 346 828 patients (median age, 65 years [IQR, 56-73 years]; 495 126 procedures [43.1%] in female patients), 750 163 (65.4%) were performed when the last hemodialysis session occurred 1 day prior to surgery, 285 939 (24.9%) when the last hemodialysis session occurred 2 days prior to surgery, and 111 744 (9.7%) when the last hemodialysis session occurred 3 days prior to surgery. Hemodialysis was also performed on the day of surgery for 193 277 procedures (16.8%). Ninety-day postoperative mortality occurred after 34 944 procedures (3.0%). Longer intervals between the last hemodialysis session and surgery were significantly associated with higher risk of 90-day mortality in a dose-dependent manner (2 days vs 1 day: absolute risk, 4.7% vs 4.2%, absolute risk difference, 0.6% [95% CI, 0.4% to 0.8%], adjusted hazard ratio [HR], 1.14 [95% CI, 1.10 to 1.18]; 3 days vs 1 day: absolute risk, 5.2% vs 4.2%, absolute risk difference, 1.0% [95% CI, 0.8% to 1.2%], adjusted HR, 1.25 [95% CI, 1.19 to 1.31]; and 3 days vs 2 days: absolute risk, 5.2% vs 4.7%, absolute risk difference, 0.4% [95% CI, 0.2% to 0.6%], adjusted HR, 1.09 [95% CI, 1.04 to 1.13]). Undergoing hemodialysis on the same day as surgery was associated with a significantly lower hazard of mortality vs no same-day hemodialysis (absolute risk, 4.0% for same-day hemodialysis vs 4.5% for no same-day hemodialysis; absolute risk difference, -0.5% [95% CI, -0.7% to -0.3%]; adjusted HR, 0.88 [95% CI, 0.84-0.91]). In the analyses that evaluated the interaction between the hemodialysis-to-procedure interval and same-day hemodialysis, undergoing hemodialysis on the day of the procedure significantly attenuated the risk associated with a longer hemodialysis-to-procedure interval (P<.001 for interaction).

Conclusions and Relevance

Among Medicare beneficiaries with end-stage kidney disease, longer intervals between hemodialysis and surgery were significantly associated with higher risk of postoperative mortality, mainly among those who did not receive hemodialysis on the day of surgery. However, the magnitude of the absolute risk differences was small, and the findings are susceptible to residual confounding.

The effect of hyperkalemia and long inter-dialytic interval on morbidity and mortality in patients receiving hemodialysis: a systematic review

BACKGROUND

Patients with chronic kidney disease, especially those receiving hemodialysis (HD), are at risk of hyperkalemia (HK). This systematic review aimed to evaluate the prevalence of HK in patients with renal disease receiving HD and collate evidence on the effect of HK and differing HD patterns (i.e., long vs. short inter-dialytic intervals [LIDI and SIDI, respectively] in a thrice weekly schedule) on mortality.

METHODS

Comprehensive searches were conducted across six databases and selected conference proceedings by two independent reviewers up to September 2020. A hundred and two studies reporting frequency of HK, mortality, or cardiovascular (CV) outcomes in adult patients with acute, chronic or end-stage renal disease in receipt of HD were included. Narrative synthesis of results was undertaken with key findings presented in tables and figures.

RESULTS

Median prevalence of HK in patients with renal disease receiving HD was 21.6% and increased in patients receiving concomitant medications - mainly renin-angiotensin-aldosterone system inhibitors and potassium-sparing diuretics. Associations between elevated potassium levels and increased risk of both all-cause and CV mortality in the HD population were consistent across the included studies. In addition, there was a rise in all-cause and CV mortality on the day following LIDI compared with the day after the two SIDIs in patients on HD.

CONCLUSIONS

Evidence identified in this systematic review indicates a relationship between HK and LIDI with mortality in patients with renal disease receiving HD, emphasizing the need for effective monitoring and management to control potassium levels both in emergency and chronic HD settings.

Dietary Potassium Intake and Mortality in a Prospective Hemodialysis Cohort

OBJECTIVES

Among hemodialysis patients, clinical practice guidelines recommend dietary potassium restriction given concerns about potential hyperkalemia leading to malignant arrhythmias and mortality. However, there are sparse data informing recommendations for dietary potassium intake in this population. We thus sought to examine the relationship between dietary potassium intake and death risk in a prospective cohort of hemodialysis patients.

DESIGN AND METHODS

Among 415 hemodialysis patients from the prospective "Malnutrition, Diet, and Racial Disparities in Chronic Kidney Disease" cohort recruited across 16 outpatient dialysis clinics, information regarding dietary potassium intake was obtained using Food Frequency Questionnaires administered over October 2011 to March 2015. We first examined associations of baseline dietary potassium intake categorized as tertiles with mortality risk using Cox regression. We then examined clinical characteristics associated with low dietary potassium intake (defined as the lowest tertile) using logistic regression.

RESULTS

In expanded case-mix Cox analyses, patients whose dietary potassium intake was in the lowest tertile had higher mortality (ref: highest tertile) (adjusted hazard ratio 1.74, 95% confidence interval 1.14-2.66). These associations had even greater magnitude of risk following adjustment for laboratory and nutritional covariates (adjusted hazard ratio 2.65, 95% confidence interval 1.40-5.04). In expanded case-mix restricted cubic spline analyses, there was a monotonic increase in mortality risk with incrementally lower dietary potassium intake. In expanded case-mix logistic regression models, female sex; higher serum bicarbonate; and lower dietary energy, protein, and fiber intake were associated with low dietary potassium intake.

CONCLUSIONS

In a prospective cohort of hemodialysis patients, lower dietary potassium intake was associated with higher mortality risk. These findings suggest that excessive dietary potassium restriction may be deleterious in hemodialysis patients, and further studies are needed to determine the optimal dietary potassium intake in this population.

Hyperkalemia: pathophysiology, risk factors and consequences

There have been significant recent advances in our understanding of the mechanisms that maintain potassium homoeostasis and the clinical consequences of hyperkalemia. In this article we discuss these advances within a concise review of the pathophysiology, risk factors and consequences of hyperkalemia. We highlight aspects that are of particular relevance for clinical practice. Hyperkalemia occurs when renal potassium excretion is limited by reductions in glomerular filtration rate, tubular flow, distal sodium delivery or the expression of aldosterone-sensitive ion transporters in the distal nephron. Accordingly, the major risk factors for hyperkalemia are renal failure, diabetes mellitus, adrenal disease and the use of angiotensin-converting enzyme inhibitors, angiotensin receptor blockers or potassium-sparing diuretics. Hyperkalemia is associated with an increased risk of death, and this is only in part explicable by hyperkalemia-induced cardiac arrhythmia. In addition to its well-established effects on cardiac excitability, hyperkalemia could also contribute to peripheral neuropathy and cause renal tubular acidosis. Hyperkalemia-or the fear of hyperkalemia-contributes to the underprescription of potentially beneficial medications, particularly in heart failure. The newer potassium binders could play a role in attempts to minimize reduced prescribing of renin-angiotensin inhibitors and mineraolocorticoid antagonists in this context.

Dialysis Prescription and Sudden Death

In the United States, end-stage renal disease patients receiving hemodialysis have an exceedingly high risk of sudden cardiac death (SCD), accounting for 29% of death events, likely relating to their uremic milieu, recurring exposure to fluid and electrolyte fluxes, and underlying cardiovascular pathology. Furthermore, epidemiologic studies have shown that SCD events, as well as mortality and hospitalizations, occur most frequently on the first dialysis day after the long interdialytic gap, suggesting that abrupt fluctuations in the accumulation and removal of electrolytes, fluid, and uremic toxins over the dialysis cycle may be contributory. Some population-based observational studies have suggested that lower dialysate potassium concentrations appear to be associated with a heightened risk of postdialysis cardiac arrest in hemodialysis patients, although the optimal serum-to-dialysate potassium gradient remains unclear. Some observational studies have suggested that low dialysate calcium concentrations and high serum-to-dialysate calcium gradients may predispose patients to SCD. There is ongoing controversy about an association between higher dialysate bicarbonate concentrations and higher risk of cardiac arrest, likely owing to confounding by indication. Some observational studies also have shown that large interdialytic weight gains, fluid retention, and high ultrafiltration rates are linked with higher risk of SCD and mortality. However, there remains considerable controversy regarding the pros and cons of designating a specific upper ultrafiltration limit with extended treatment times as a clinical practice measure, and further studies are needed to define the optimal tools, metrics, targets, and implementation measures for volume control in the hemodialysis population. In this review, we highlight the epidemiology and pathophysiology of how specific aspects of the hemodialysis procedure may relate to the risk of SCD, as well as preventative strategies and future research directions that can address this risk.

Dialysate Potassium and Mortality in a Prospective Hemodialysis Cohort

BACKGROUND

Studies examining the association of dialysate potassium concentration and mortality in hemodialysis patients show conflicting findings. We hypothesized that low dialysate potassium concentrations are associated with higher mortality, particularly in patients with high pre-dialysis serum potassium concentrations.

METHODS

We evaluated 624 hemodialysis patients from the prospective Malnutrition, Diet, and Racial Disparities in Kidney Disease study recruited from 16 outpatient dialysis facilities over 2011-2015 who underwent protocolized collection of dialysis treatment characteristics every 6 months. We examined the association of dialysate potassium concentration, categorized as 1, 2, and 3 mEq/L, with all-cause mortality risk in the -overall cohort, and stratified by pre-dialysis serum potassium (< 5 vs. ≥5 mEq/L) using case-mix adjusted Cox models.

RESULTS

In baseline analyses, dialysate potassium concentrations of 1 mEq/L were associated with higher mortality, whereas concentrations of 3 mEq/L were associated with similar mortality in the overall cohort (reference: 2 mEq/L): adjusted hazard ratios (aHRs; 95% CI) 1.70 (1.01-2.88) and 0.95 (0.64-1.39), respectively. In analyses stratified by serum potassium, baseline dialysate potassium concentrations of 1 mEq/L were associated with higher mortality in patients with serum potassium ≥5 mEq/L but not in those with serum potassium < 5 mEq/L: aHRs (95% CI) 2.87 (1.51-5.46) and 0.74 (0.27-2.07), respectively (p interaction = 0.04). These findings were robust with incremental adjustment for serum potassium, potassium-binding resins, and potassium-modifying medications.

CONCLUSION

Low (1 mEq/L) dialysate potassium -concentrations were associated with higher mortality, particularly in hemodialysis patients with high pre-dialysis serum potassium. Further studies are needed to identify therapeutic strategies that mitigate inter-dialytic serum potassium accumulation and subsequent high dialysate serum potassium gradients in this population.