Assessing adequacy of hemodialysis: Urea modeling

Abstract

A 73-year-old Asian-American woman with end-stage renal disease (ESRD) was evaluated for inordinately high urea distribution volumes (V) calculated on the basis of single-compartment modeling of data obtained from several hemodialyses (Table 1). The patient's renal failure and hypertension had been managed with hemodialysis and antihypertensive medications for 4 years. The cause of renal failure was type-Il diabetes mellitus, which also had resulted in retinopathy and poor vision; a brother and 3 sisters also had diabetes mellitus and hypertension. Two years previously she had had increasing angina that improved after coronary angioplasty. A chest radiograph showed cardiomegaly and aortic calcification. One year previously she had had persistent, non-healing ulcers on the plantar surface of the right foot that resolved following percutaneous angioplasty of the right femoral artery. During the month preceding evaluation, her average blood pressure was 161/83 mm Hg predialysis and 142/74 mm Hg postdialysis. At the time of evaluation, her physical examination was remarkable for a holosystolic murmur at the left sternal border that radiated to the axilla. She had an easily palpable thrill and a high-pitched bruit at the mid-portion of her left forearm loop Gore-Tex graft. Pedal pulses were barely palpable; no peripheral edema was present. Hemodialysis was prescribed for 3 hours thrice weekly with a high-flux polysulfone dialyzer (1.8 square meter surface area). Dialysate flow was set at 500 mI/mm and blood flow averaged 350 mI/mm; the expected urea clearance was 245 mI/mm at these flow rates. Heparin was limited to 750 units/hr infused intravenously during each hemodialysis, but administered no later than 30 minutes before the end of