This study is the first to examine serum potassium levels in patients on maintenance hemodialysis in China using the new diagnostic criterion for hyperkalemia. Our results show that the incidence of hyperkalemia in these patients is 38.81%, suggesting that hyperkalemia is still a very common complication and requires attention. A French multi-center study showed that 57.6% of similar patients relapsed within 1 month, and 73.2% would relapse within 3 months, leading to an increase in the number of individuals requiring dialysis. Because hyperkalemia can induce arrhythmias and even lead to sudden death,6 it is critical to prevent the occurrence of hyperkalemia. The present study shows that high systolic blood pressure, decreased residual urine volume, high pre-dialysis blood urea nitrogen, low pre-dialysis CO2 binding capacity, and the use of ACEi/ARB drugs are independent risk factors for hyperkalemia.
Under normal circumstances, potassium is mainly excreted through urine. In the present study, the residual urine volume of patients in the hyperkalemia group was significantly reduced. Because residual urine volume is an independent risk factor for the development of hyperkalemia, its protection will help prevent this complication.7 Moreover, the distribution of blood potassium in and out of cells is significantly related to the acid–base balance of the extracellular fluid. In patients on hemodialysis, metabolic acidosis often occurs owing to disordered excretion of organic acids. In such cases the patient's CO2CP will drop significantly and, through the H-K ion exchange on the cell membrane, extracellular potassium ion levels will increase, resulting in hyperkalemia. This study also shows that a decreasing CO2CP is an independent risk factor for hyperkalemia. Therefore it is important to monitor acidosis strictly, thereby avoiding the occurrence of hyperkalemia.8,9
Blood urea nitrogen is often related to metabolism and diet. High blood urea nitrogen often means that patients are in a high metabolic state or eat more nitrogen-containing foods. Our research shows that blood urea nitrogen is positively correlated with blood potassium and is an independent risk factor, suggesting that high metabolism and an excessive intake of nitrogen-containing foods may be important contributors to the development of hyperkalemia.10,11
Our study also shows that patients with hyperkalemia have significantly higher systolic and diastolic blood pressures than those without hyperkalemia; the usage rate of ACEIs/ARBs was also significantly greater among such patients, making this an additional independent risk factor.11,12 The usage rate of ACEIs/ARBs in patients on hemodialysis is very high. About 45.58% of our patients overall were being treated with these drugs, whereas among those with hyperkalemia, this rate reached the significantly higher level of 52.00%. Therefore serum potassium in patients using ACEIs/ARBs should be especially closely monitored. Many studies have suggested that even though the use of ACEIs/ARBs in patients with renal insufficiency will lead to the occurrence of hyperkalemia, they have clear protective effects on the heart and kidney; thus, their discontinuation can accelerate the loss of renal function and increase the incidence of cardiovascular events.13,14 In this regard, there are guidelines suggesting that, for hyperkalemic patients who are concurrently taking ACEIs/ARBs, oral potassium-lowering drugs can be used to maintain normokalemia.9,15
Our research also shows that some patients on hemodialysis still have hypokalemia, and hypokalemia also affects the long-term prognosis of patients on hemodialysis. Therefore, serum potassium must be closely monitored.
Our study has some limitations. First, it is a cross-sectional survey, and the relationship between serum potassium and long-term prognosis cannot be determined. Further follow-up of each patient's prognosis will be needed. Second, we did not count the interval between a patient's blood draw and his or her previous dialysis, and the length of the dialysis interval is also a factor that affects the level of serum potassium.
Our study shows that the incidence of hyperkalemia is still very high in the area of Foshan City, China, even when 5.0 mmol/L is used as the diagnostic standard. It is, therefore, necessary to emphasize measures that will strengthen the control of serum potassium. We found that the independent risk factors affecting the development of hyperkalemia include systolic blood pressure, residual urine volume, pre-dialysis blood urea nitrogen, pre-dialysis CO2 binding capacity, and the use of ACEIs/ARBs. Thus, these risk factors must be closely monitored.