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- Title
Radionuclide method for evaluating the performance of hemodialysis in vivo.
- Authors
Bihl, Geoffrey R.; Bird, Nicholas J.; Peters, Christina; Bradley, John R.; Peters, A. Michael
- Abstract
Radionuclide method for evaluating the performance of hemodialysis in vivo.Background.Specifications of dialyzer performance are generally based on in vitro measurements. There is, however, a shortage of data on dialyzer performance in vivo. The aim of this study was to use continuous measurement of technetium-99m-diethyltriaminepentaacetic acid (Tc-99m-DTPA) blood concentration as a means of continuously monitoring dialyzer function in vivo in patients undergoing routine hemodialysis.Methods.The study population comprised 15 patients (45 to 80 years old; 13 males). Tc-99m-DTPA was administered intravenously 90 minutes before obtaining a blood sample and starting dialysis. Blood Tc-99m-DTPA activity was continuously monitored by passing the line carrying blood from the patient to the dialyzer close to a scintillation probe mounted in a shielded housing. At the end of hemodialysis, lasting 180 to 300 minutes, chromium-51-ethylenediaminetetraacetic acid (Cr-51-EDTA) was given intravenously and a blood sample taken 90 minutes later. Baseline dialyzer blood flow (Qb) and dialysate flow (Qd) were 250 to 350 mL/min and 500 mL/min, respectively. The rate constant,α, of the decrease in blood Tc-99m-DTPA activity was used as the measure of moment-to-moment dialyzer function. Pre- and postdialysis extracellular fluid volumes were calculated from the blood Tc-99m-DTPA and Cr-51-EDTA concentrations (VDTPA and VEDTA) before and after dialysis. Tc-99m-DTPA clearance was measured as the product ofα and VDTPA. Dialyzer urea clearance was calculated from pre- and postdialysis urea nitrogen concentrations and the time of dialysis. The effects of brief changes in Qb and Qd on dialyzer function were assessed from the associated changes inα.Results.The Tc-99m-DTPA clearance profile was biexponential, becoming monoexponential about 1 hour after starting hemodialysis, withα remaining constant for as long as dialysis continued in five patients in whom Qb and Qd were left unaltered. Mean (SEM) plasma Tc-99m-DTPA clearance averaged over the entire period of dialysis in all 15 patients was 110 (3.1) mL/min. It correlated with urea clearance (r= 0.71) (P<0.01) which was 225 (9.5) mL/min based on a total body water of 2.5 that of VDTPA and 212 (13) mL/min scaled to 40 L/1.73 m2. Extracellular fluid volume decreased by 1.73 (0.74) l over dialysis, which was comparable to the change in weight[1.48 (0.57) kg]. The extraction fraction of Tc-99m-DTPA across the artificial kidney, directly measured from afferent and efferent blood samples under baseline Qb and Qd, was 0.5 (0.013). Average extraction fraction indirectly estimated from Tc-99m-DTPA blood clearance and Qb was 0.54 (0.019). These two measurements of extraction fraction correlated with each other under conditions of varying Qb and Qd (r= 0.74) (N= 27) (P<0.001). Changes inα resulting from changes in Qb and Qd were similar to changes predicted from computerized modeling. The ratio of mass transfer coefficients of urea and Tc-99m-DTPA with respect to the dialyzer, calculated as if they were permeability-surface area products, was 3.3, similar to the ratio, obtained from the literature, in continuous capillary endothelium.Conclusion. Tc-99m-DTPA is a useful agent for continuously monitoring dialyzer function in vivo and provides a platform for the use of other radio-pharmaceuticals of different molecular sizes that could be used in an analogous fashion.
- Subjects
HEMODIALYSIS; BLOOD filtration; ETHYLENEDIAMINETETRAACETIC acid; NITROGEN excretion; HEMODYNAMICS; BLOOD flow
- Publication
Kidney International, 2005, Vol 67, Issue 2, p721
- ISSN
0085-2538
- Publication type
Article
- DOI
10.1111/j.1523-1755.2005.67133.x