Fluid Overload in Dialysis Patients

Park, Min Sun; Lee, Eun Ah

Abstract

End-stage renal disease(ESRD) is the fatal retention of non-volatile, metabolic waste products, salt, and water due to extensive loss of functioning nephrons. Renal replacement therapy is primarily aimed to remove retained waste products and fluid. Adequacy of dialysis is the dose of dialysis below which one observes a significant worsening of morbidity and mortality. Urea kinetic modeling, Kt/Vurea, etc. is regarded as a quantitative guideline of dialysis adequacy in both hemodialysis(HD) and peritoneal dialysis(PD). Water is one of the most important uremic toxin retained in ESRD patients. The importance of fluid overload on morbidity and/or mortality in dialysis patients is yet to be evaluated. Recent technology of HD provides adequate Kt/ Vurea for relatively short dialysis time and higher patient survival. Blood pressure control and extracellular fluid(ECF) volume are closely related with dialysis time in HD patients. Short dialysis time, 3-4 hours per session may not enough to control blood pressure. Hypertension is an important risk factor of survival in dialysis patients. Fluid overload is the most important factor of hypertension in dialysis patients. Patients with uncontrolled hypertension have higher mortality rate despite similar Kt/Vurea compared with patients with good blood pressure control. A longer dialysis time improves ECF volume and blood pressure control and decreases cardiovascular mortality. Continuous ambulatory peritoneal dialysis(CAPD) is a slow continuous therapy and is believed to maintain better control of ECF volume and blood pressure compared with hemodialysis. ECF volume and blood pressure controls are improved after initiation of CAPD, however, return to pre-CAPD levels after a few years of CAPD when residual renal function disappears. Patients transferred to hernodialysis from CAPD lose around 4kg of body weight for a few months on HD. Approximately 25% of CAPD patients are clinically fluid overloaded. Increased peritoneal permeability is an independent risk factor for patient and technique survivals in CAPD patients. Fluid overload in CAPD patients with increased peritoneal pernability is believed to be an important underlying mechanism of increased mortality and technique failure in this group. In conclusion, fluid overload is an important risk factor of mortality in dialysis patients. Sufficient dialysis time resulting good controls of ECF volume and blood pressure in hemodialysis patients and individualized dialysis prescription according to the peritoneal permeability in CAPD patients are vital to provide adequate dialysis and to decrease cardiovas-cular mortality.