Monitoring relative fluid balance alterations in haemodialysis of diabetic patients by electrical impedance

Abstract

Measurements of total-body electrical impedance in the frequency range between 200 Hz and 300 kHz were performed on 37 diabetic patients undergoing chronic haemodialysis. Special attention was paid to the instrument design, where a self-balancing differential current source was used, reducing considerably the common-mode voltage at the amplifier input. The patient-instrument interface includes screened leads, separately driven by unity-gain buffers. The measurement error was < 1% for the impedance within the range of 20 to 1000 omega and < 0.3 degree (mean) for the phase angle. Impedance/phase and ultrafiltration measurements were carried out throughout the entire procedure. Total and extracellular water were computed and compared with extracted fluid volumes. The trends of change of the extracellular and intracellular fluid volumes during and immediately after dialysis corresponded to the respective clinical condition of the patients and enabled us to divide them into four groups. This approach is a step toward continuous monitoring and adaptive treatment, tailored to the individual patient needs.