New radioactive tracer method for automatic continuous monitoring of the rate of hemodialysis

The progress of hemodialysis is monitored by selecting a glomerular substance, such as DTPA, that is removed by the artificial kidney at a realistic rate and labelling it with a radioisotope, preferably Tc99m, that gives a low patient radiation dose and is easy to measure. The Tc99m-DTPA is injected intravenously and allowed to equilibrate in the patient. Hemodialysis is then started with a conventional dialyzer. The isotope concentration is measured with a simple scintillation counter, 3 or 4 turns of the bloodfilled plastic tubing between the patient and dialyzer being wrapped around the detector crystal. The counting rate is a measure of the fraction of Tc99m-DTPA remaining in the patient. The drop in counting rate due to the radioactive decay of the isotope is automatically compensated by a novel ratemeter whose sensitivity increases with time at the appropriate exponential rate. Its output indicator is set to 100% at the start of dialysis and decreases as the isotope is removed, being about 35% after 6 hours. By watching the meter the dialysis may be terminated at any desired level. Thirteen patients have been studied with good results. This technique is simple to use and presents no contamination or radiation hazard to the patient. It has potential clinical application for hospital and home dialysis of patients with chronic kidney failure.