Tc-99m-DTPA - a new Test Substance for Detoxification Devices

Tc^99m labeled diethylenetriaminepentaacetic acid (Tc-99m-DTPA) is an appropriate in vivo test solute for all extracorporeal detoxification procedures. The molecular weight of the Tc-99m-DTPA complex is within the biologically relevant middle molecular range of 400 to 700 daltons. Tc-99m-DTPA is distributed in the extracellular space in the same way as inulin. Regarding its localization in the gel filtration spectra and plasma clearance, Tc-99m-DTPA corresponds to middle molecule peak 2.

The evaluation of elimination rate and plasma clearance C_P of Tc-99m-DTPA is possible by measuring the pulse rates before and after the detoxification device. Taking into account the corrections for Ht and UFR, the Tc-99m-DTPA plasma clearances were calculated for different dialyzers, high flux dialyzers, hemofilters and a hemoperfusion device.

The continuous measurement of pulse rates and the use of a UFR-controller (A2008) allow an exact tracking of C_P vs. time, the estimation of C_P(Q_B), C_P(UFR) and of the sieving coefficient. Examples are given for these cases.

It was shown that an increase in plasma clearance to more than about 100 ml/min does not greatly increase the Tc-99m-DTPA elimination rate.