Tc-99m-DTPA--a new test substance for detoxification devices.

Tc99m 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 CP 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 CP vs. time, the estimation of CP (QB), CP(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.