Pre- to post-dialysis potassium gradient and mortality in patients on hemodialysis: A propensity-matched analysis

Introduction: Pre- to post-dialysis potassium gradient (Delta K) has arrhythmogenic effects; however, its effect on mortality remains unclear. The relationship between Delta K and mortality was assessed. Methods: All patients undergoing hemodialysis in Beijing in 2014 were eligible for inclusion. The low (<= 1.2 mmol/L), median (1.2-1.8 mmol/L), and high (>1.8 mmol/L) Delta K groups were matched by sex, age, diabetes, and dialysis time for enrollmen. The primary and secondary outcomes were all-cause and cardiovascular death within the follow-up. Cox regression analysis was performed to evaluate the effect of Delta K on mortality. We also analyzed the associations of combinations of Delta K and pre-dialysis potassium with mortality. Results: We enrolled 2181 patients in three matched groups (n = 727 per group). The median follow-up was 72.0 (interquartile range, 53.7-72.0) months. All-cause mortality occurred in 215/727 (29.6%), 95/727 (13.1%), and 198/727 (27.2%) patients in the low-, median-, and high-Delta K groups, respectively. After adjusting for multiple factors, the median Delta K group had better survival than the low- (hazard ratio (HR), 1.91; 95% confidence interval [95% CI], 1.45-2.52; p < 0.001) and high-Delta K groups (HR, 2.17; 95% CI, 1.57-2.99; p < 0.001). Further analysis based on pre-dialysis potassium revealed that when maintaining a level of 4.5-5.5 mmol/L and Delta K of 1.2-1.8 mmol/L, patients had the lowest risk of mortality, whereas the highest risk was observed when pre-dialysis potassium was >5.5 mmol/L and Delta K was >1.8 mmol/L. Conclusion: Maintaining serum potassium within a appropriate range and reducing potassium fluctuations during dialysis may help to reduce the mortality risk of maintenance hemodialysis patients. These findings provide important data support for the quality control of hemodialysis.