Postdialysis Hypokalemia and All-Cause Mortality in Patients Undergoing Maintenance Hemodialysis

Abstract

Background and objectives: Almost half of patients on dialysis demonstrate a postdialysis serum potassium ≤3.5 mEq/L. We aimed to examine the relationship between postdialysis potassium levels and all-cause mortality.

Design, setting, patients, & measurements: We conducted a cohort study of 3967 participants on maintenance hemodialysis from the Dialysis Outcomes and Practice Patterns Study in Japan (2009-2012 and 2012-2015). Postdialysis serum potassium was measured repeatedly at 4-month intervals and used as a time-varying variable. We estimated the hazard ratio of all-cause mortality rate using Cox hazard regression models, with and without adjusting for time-varying predialysis serum potassium. Models were adjusted for baseline characteristics and time-varying laboratory parameters. We also analyzed associations of combinations of pre- and postdialysis potassium with mortality.

Results: The age of participants at baseline was 65±12 years (mean±SD), 2552 (64%) were men, and 96% were treated with a dialysate potassium level of 2.0 to <2.5 mEq/L. The median follow-up period was 2.6 (interquartile range, 1.3-2.8) years. During the follow-up period, 562 (14%) of 3967 participants died, and the overall mortality rate was 6.7 per 100 person-years. Compared with postdialysis potassium of 3.0 to <3.5 mEq/L, the hazard ratios of postdialysis hypokalemia (<3.0 mEq/L) were 1.84 (95% confidence interval, 1.44 to 2.34) in the unadjusted model, 1.44 (95% confidence interval, 1.14 to 1.82) in the model without adjusting for predialysis serum potassium, and 1.10 (95% confidence interval, 0.84 to 1.44) in the model adjusted for predialysis serum potassium. The combination of pre- and postdialysis hypokalemia was associated with the highest mortality risk (hazard ratio, 1.72; 95% confidence interval, 1.35 to 2.19, reference; pre- and postdialysis nonhypokalemia).

Conclusions: Postdialysis hypokalemia was associated with mortality, but this association was not independent of predialysis potassium.

Keywords: Confidence Intervals; Dialysis Solutions; Follow-Up Studies; Japan-Dialysis Outcomes and Practice Patterns Study; Potassium; Proportional Hazards Models; chronic hemodialysis; electrolytes; end-stage renal disease; hypokalemia; mortality; post-dialysis; renal dialysis; serum potassium.

Graphical abstract

Figure 1.

Flowchart of eligible and ineligible participants. The numbers of potential and eligible patients in each phase are shown on the left side. The reasons for ineligibility and the number of ineligible participants are shown on the right side.

Figure 2.

Cumulative survival was lowest in the low postdialysis K group, and other three group showed the similar cumulative survival. The definition of each groups is as follows: low, baseline postdialysis K<3.0mEq/L; medium-low, baseline postdialysis K≥3.0 to 3.5mEq/L; medium-high, postdialysis K≥3.5 to 4.0 mEq/L; high, postdialysis K≥4.0 mEq/L.

Figure 3.

Hazard ratio increased depending on severity of hypokalemia, but the association was not statistically significant (95% confidence interval included 1.0). The thick black line shows the HR of all-cause mortality. The reference (HR=1) is 3.5 mEq/L. The gray area shows the 95% CI. The model was adjusted for baseline confounders of sex, age, body mass index, comorbidities, and medications, and time-varying confounders of serum albumin, C-reactive protein, normalized protein catabolic rate, dialysis vintage, single-pool Kt/V, dialysate bicarbonate, type of vascular access, and predialysis K.

Figure 4.

The pattern of association of postdialysis hypokalemia with mortality different by baseline predialysis potassium level, but this effect modification was not statistically significant (interaction P=0.09). The numbers of patients in the high, medium, and low predialysis K groups were 790, 1892, and 1280, respectively. Five patients were excluded from this analysis because their predialysis K level was missing. The reference (HR=1) was 3.5mEq/L. The definition of subgroups is as follows: low, <4.5 mEq/L; medium, 4.5 to <5.5 mEq/L; and high, ≥5.5 mEq/L.