Serum Potassium Levels and Mortality in Hemodialysis Patients: A Retrospective Cohort Study

Abstract

Background: Hyperkalemia is common in patients receiving maintenance hemodialysis. However, few studies have examined the association between serum potassium level and mortality. Methods: This study used annual cohorts of hemodialysis patients during 2007-2010. To determine hyperkalemia prevalence, monthly hyperkalemia was defined as serum potassium level ≥5.5 mEq/l; prevalence was calculated as a ratio of hyperkalemia episodes to follow-up time, reported separately by long and short interdialytic interval. To determine the impact of hyperkalemia on mortality, patients in the 2010 cohort were followed from first potassium measurement until death or a censoring event; hyperkalemia was defined, sequentially, by potassium levels 5.5-6.0 mEq/l at 0.1 mEq/l intervals. Time-dependent Cox proportional hazards modeling was used to estimate the association between hyperkalemia and mortality. Results: The 4 annual cohorts ranged from 28,774 to 36,888 patients. Mean age was approximately 63 years, about 56% were men, 51% were white and 44% had end-stage renal disease caused by diabetes. Hyperkalemia prevalence was consistently estimated at 16.3-16.8 events per 100 patient-months. Prevalence on the day after the long interdialytic interval was 2.0-2.4 times as high as on the day after the short interval. Hyperkalemia, when defined as serum potassium ≥5.7 mEq/l, was associated with all-cause mortality (adjusted hazards ratio (AHR) 1.13, 95% CI 1.01-1.28, p = 0.037, vs. <5.7 mEq/l) after adjustment. AHRs increased progressively as the hyperkalemia threshold increased, reaching 1.37 (95% CI 1.16-1.62, p < 0.0001) for ≥6.0 mEq/l. Conclusions: The long interdialytic interval was associated with increased likelihood of hyperkalemia. Hyperkalemia was associated with all-cause mortality beginning at serum potassium ≥5.7 mEq/l; mortality risk estimates increased ordinally through ≥6.0 mEq/l, suggesting a threshold at which serum potassium becomes substantially more dangerous.

Metabolic and volume status evaluation of hemodialysis patients with and without residual renal function in the long interdialytic interval

“…It is important to emphasize two factors that demonstrate the great vulnerability of patients without RRF during the LII. The first is related to the fact that the morbimortality associated with hyperkalemia in patients on HD is even more significant when potassium values are above 6 mEq/L, which occurred in 83% of patients without RRF in our study 24,25 . The second was the large variation of serum potassium levels in these patients throughout the LII, since, although starting from values similar to those of patients with RRF at the beginning of the interval, they reached significantly higher values at the end, which exposed them to a higher electrolyte gradient during HD session and increased the risk of adverse events 9 .…”

“…One of the possible explanations for this is that these data, unlike ours, were not obtained exclusively after the LII, when serum potassium levels are generally higher than in the middle of the week. In this regard, Yusuf et al 24 found a 2 to 2.4-fold higher prevalence of hyperkalemia after the LII when compared to the short interval, in a cohort of American dialysis patients between 2007 and 2010. However, in the data obtained from DOPPS (Dialysis Outcomes and Practice Patterns Study, which assessed data from 20 countries between 1996 and 2015), the difference between serum potassium levels obtained after the long and short interdialytic interval ranged from only 0.01 mEq/L in China to 0.19 mEq/L in Germany 25 .…”

Elevated baseline potassium level within reference range is associated with worse clinical outcomes in hospitalised patients

“…Few previous studies have considered the impact of elevated serum K + level, with most of them focussing on the relationship between serum K + levels and adverse prognosis in patients with cardiovascular or chronic kidney diseases 8, 11, 12, 21–23 . Among these studies, there were evidences showing the clinical significance of elevated serum K + levels, i.e., >4.7 mmol/L or >4.0 mmol/L, for worse patient prognosis 9, 10, 19 .…”

“…This electrolyte imbalance is prevalent in patients with cardiovascular disease or impaired kidney function 3, 4 , and the recent use of several medications related to serum potassium (K + ) levels has further increased its incidence 5–7 . Moreover, hyperkalaemia is associated with worse prognosis and can induce critical arrhythmia 8–12 . Hence, management of this electrolyte imbalance has been suggested in clinical guidelines and is widely practised 13–15 .…”

Briefly Noted

“…An analysis of two large dialysis data bases found that hyperkalemia (≥5.5 mEq/l) was found about 17 times per 100 patient‐months and was 2.0–2.4 times more likely after the long versus short interdialytic interval .…”