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.

Reliability of the fluid balance in neonates

“…This study shows that keeping a fluid balance on a neonatal high‐care ward shows poor agreement with daily changes in body weight, with more than 40% of the comparisons showing clinically relevant differences. Our findings confirm earlier reports in adults showing poor agreement of fluid balance with changes in body weight (4,5,13), central venous monitoring (14) or bioelectrical impedance measurements (15).…”

Possibilities for predictive measurement of the transthoracic impedance in defibrillation

“…An in-house developed instrument for bioimpedance spectroscopy in the frequency range of 500 Hz to 300 kHz and impedance range of 0 -1000 O [12] was used. In this application the transthoracic impedance modulus was measured at ve frequencies, 10, 20, 50, 100 and 300 kHz, by the two-electrode con guration.…”

Monitoring of fluctuating airway obstruction and episodes of coughing by thoracic electrical impedance

“…The impedance range is 0 to 127.5X and the operating current peak-topeak amplitude is 2 mA. The maximum allowable current source load can reach 3 kX ( abou t 1.5 kX per injecting electrode) , with a supply voltage of 6 6 V. The use of a differential voltage-to-current converter results in a considerable reduction of the in uence of parasitic impedances in the patient -instrument connection circuit ( electrode -skin impedances, cable and stray capacitances, current generator output and ampli er input impedances) [7,8]. The output impedance of the current source and the input impedance of the ampli er exceed 5 MX .…”

“…The current injecting electrodes are located along the axillary line about 5 cm under the ax illae and the voltage take-off electrodes are placed alongside at about 1.5 cm medially. The large size of the electrodes, combin ed with the high impedance differential voltage-to-current converter and ampli er allow for considerable suppression of motion artefacts [1,7]. The strongest ones, provoked by arm movements, body position and posture can reach 3 -5% of Z0.…”