LAUSR

Potassium (K) is mostly an intracellular ion, with a complex homeostasis that is deeply modified in ESRD patients undergoing hemodialysis (HD). Several factors (diet, insulin, acid-base balance, aldosterone, etc) may contribute to determine the level of serum extracellular K, but it is not clear which factor contributes the most. We aimed to evaluate the importance of several factors in inducing hyperkalemia in HD patients. Chronic tri-weekly HD patients were evaluated. Patients on diuretics or on potassium binders were excluded. For every patient we recorded age, sex, Kt/V and we measured the post-HD kalemia on the day before the long interHD interval. On the day after the long interHD interval we evaluated: pre-HD K, glucose, creatinine, aldosterone, LDH, CPK, arterial blood gases, ECG, overhydration by bioelectrical impedance analysis, body weight increase after the long interHD interval and daily urinary output. K amount introduced by diet was calculated by a dietitian from each patient’s daily food diary. Treatment with ARB, ACE-inhibitors, beta-blockers, insulin or heparin was recorded. Data are presented as mean±SD for each variable analyzed. Correlations between the serum K values and change in serum K (delta K) and the other patient medical data were determined through the two-tailed Pearson’s test or Spearman test according to data distribution. We enrolled 56 patients (male 53.6%), aged 72±13, with a mean Kt/V 1.44±0.25. Mean post-HD kalemia was 3.65±0.4 mmol/L, mean pre-HD kalemia was 5.23±0.72 mmol/L, with a mean delta 1.58±0.64 mmol/L. Medium pH was 7.37±0.01, with serum bicarbonate 20.15±4.0 mmol/L. Overhydration estimated by bioelectrical impedance analysis was 2.3±0.6 L, while mean daily intake of K was 1697.13±711.13 mg. We found a strong positive correlation between delta K and pre-HD kalemia (r=0.79, p<0.0001). Surprisingly, a positive correlation was found between delta K and serum bicarbonate (r=0.27, p=0.04), while no correlations were present between delta K, mean pre-HD kalemia and dietary intake of K (p=ns). No difference in delta K was found between anuric and not anuric patients. No other statistically significant differences were found. Potassium homeostasis is markedly altered in ESRD and several factors contribute to determine the serum K values. In this study we found that delta potassium correlates to pre-HD kalemia. We did not study the temporal kinetic of K increase, but it is reasonable to infer that a significant post-HD rebound may contribute to increase kalemia, as dietary intake of K was not found to correlate to delta K or to serum K after the long interdialytic interval. The positive correlation between delta K and serum bicarbonate is unexpected and difficult to explain. However, since we did not measure serum bicarbonate post-HD, we may speculate that patients with high delta K and serum bicarbonate might have even higher levels of bicarbonate after HD. In conclusion, our study shows that none of the examined factors prevales in determining high serum potassium in HD patients.