Urea kinetic modeling at high urea clearances: implications for clinical practice.
The original description of urea kinetic modeling in hemodialysis was based on a single pool of fluid equal to total body water. This assumption is valid only if the rate of transport between compartments is sufficiently rapid compared with the rate of urea removed by hemodialysis. We have reexamined the issue of urea compartmentation using 10 patients with initial BUN values ranging from 28 to 101 mg/dL who were studied while on high flux hemodiafiltration. Sampling was carried out at times as short as 1 minute after the beginning of the treatment. In 4 patients, samples were also drawn after the dialysis ended. The measured BUN values were used to fit a two-compartment, variable-volume kinetic model. The mean urea diffusive clearance of the dialyzer during the treatment was 503 mL/minute, and the bidirectional urea clearance between compartments was 1,282 mL/minute. The percentage of total body water in the rapidly exchangeable compartment was 35.4%. Comparison with a one-compartment, variable-volume model showed a statistically better fit for all patients with the more complex model. In the 4 patients studied in the postdialysis period, the rebound in BUN ranged from 22% to 24%. These studies show that, at high urea clearances, the urea distribution space and, therefore, dialysis modeling requires two compartments. These results explain the majority of the rebound in urea concentration observed 30 to 60 minutes following the discontinuation of the dialysis treatment and point out an improved strategy for monitoring the efficiency of the treatment delivered to the patient.
Abramson
F
F
Department of Pharmacology, George Washington University Medical Center, Washington, DC 20037, USA.
Gibson
S
S
Barlee
V
V
Bosch
J P
JP
D001806:Blood Urea Nitrogen; D001835:Body Weight; D003201:Computers; D017583:Hemodiafiltration; D006801:Humans; D007676:Kidney Failure, Chronic / Q000378:metabolism* / Q000628:therapy; D007700:Kinetics; D008954:Models, Biological; D014508:Urea / Q000378:metabolism*
D014508:Urea