A Differential Transformer for Noninvasive Continuous Sodium Monitoring During Dialysis Treatment

During dialysis treatment with individual sodium profiles, in which the dialysate sodium concentration is changed over time and consequently the blood sodium concentration, continuous monitoring of the sodium blood concentration is important. The current practice is to analyze blood samples in the laboratory or using a blood gas analyzer. This way, quasi-continuous monitoring requires a considerable amount of personnel effort and costs. Moreover, the results are just available with a time delay. In this paper, we present a low-cost PCB differential transformer for continuous and contactless monitoring of the sodium concentration in blood during dialysis treatment. The PCB differential transformer monitors the conductivity of blood as a measure of the sodium concentration. This is a reasonable approach since the conductivity of blood is mainly defined by the sodium concentration under physiological conditions. In preclinical experiments, we show that the sodium concentration in blood can be measured by this approach with a maximum relative error of 2.7 % referenced to a commercially available blood gas analyzer.