Refining the Model of Urea Kinetics: Compartment Effects

A 70‐year‐old female with chronic congestive heart failure requires maintenance hemodialysis because of end‐stage diabetic nephropathy. She is dialyzed on Monday, Wednesday, and Friday for 2 hours using a dialyzer with an average urea clearance of 250 ml/min. Dry weight is 50 kg. Predialysis blood urea nitrogen (BUN) on Wednesday is 50 mg/dl; postdialysis BUN is 15 mg/dl. A single‐compartment, variable‐volume model of urea kinetics revealed the following: 1.5 hours of dialysis are sufficient to maintain Kt/V at 1.1/dialysis; protein catabolism is 0.92 g/kg/day; her volume of urea distribution is 43% of body weight. Provided the blood access device and dialysis equipment are functioning properly and the blood specimens are drawn and measured correctly, are the model predictions valid?