Serum potassium and cause-specific mortality in a large peritoneal dialysis cohort

Abstract

Background and objectives: Unlike hemodialysis (HD), peritoneal dialysis (PD) is a continuous therapy and does not induce myocardial stunning. Yet, the death risk in HD and PD patients is similar. This study tested the hypothesis that serum potassium abnormalities contribute more to the death risk in PD patients than in HD patients.

Design, setting, participants, & measurements: Data from patients treated in DaVita facilities between July 1, 2001 and June 30, 2006 (n=10,468 PD patients; n=111,651 HD patients) were used to determine association of serum potassium with mortality.

Results: PD patients were significantly more likely to have serum potassium < 4 mEq/L, with an adjusted odds ratio of 3.30 (95% confidence interval [95% CI], 3.05, 3.56). There was a U-shaped relationship between time-averaged serum potassium and all-cause and cardiovascular mortality of PD patients, with adjusted hazards ratios of 1.51 for all-cause mortality for potassium < 3.5 mEq/L (95% CI, 1.29, 1.76) and 1.52 for potassium ≥ 5.5 mEq/L (95% CI, 1.32, 1.75). The population-attributable risks for all-cause mortality for serum potassium < 4.0 and ≥ 5.5 mEq/L were 3.6% and 1.9%, respectively, in PD patients, and 0.8% and 1.5%, respectively, in HD patients.

Conclusions: Abnormalities in serum potassium contribute disproportionately to the high death risk in PD patients. This may, in part, account for the equivalent cardiac risk seen with the two therapies.

Figure 1.

Distribution of serum potassium levels in patients treated with PD (n=10,468) and HD (n=111,651). The data reflect the average of all measurements made during the first 3 months of entry into study cohort. PD, peritoneal dialysis; HD, hemodialysis.

Figure 2.

Association of time-averaged serum potassium concentration with mortality in patients undergoing PD (n=10,454). (A) All-cause mortality, (B) cardiovascular mortality, and (C) and infection-related mortality. Reference group: PD patients with time-averaged serum potassium levels between 4.0 and <4.5 mEq/L. Error bars represent 95% confidence intervals. PD, peritoneal dialysis.

Figure 3.

Association of serum potassium, use as a time-varying covariate, with mortality in patients undergoing peritoneal dialysis (n=10,454). Error bars represent 95% confidence intervals.

Figure 4.

Association of time-averaged serum potassium concentration with outcomes in patients undergoing PD (n=10,454) and HD (n=111,434). (A) All-cause mortality, (B) cardiovascular mortality, and (C) infection-related mortality. Reference group: hemodialysis patients with serum potassium levels between 4.0 and <4.5 mEq/L. PD, peritoneal dialysis; HD, hemodialysis.