Hematocrit measurement - a high precision on-line measurement system based on impedance spectroscopy for use in hemodialysis machines

Abstract

This paper presents a unique technical approach to measure the proportion of blood volume occupied by red blood cells, the hematocrit value (HCT) on-line and in-line. A practical method has been developed to measure without the need for extracting blood samples out of an existing extracorporeal blood circulation system. The new sensor is based on Impedance Spectroscopy and measures electrical properties of the blood at various frequencies. In order to achieve the required precision resolution the sensor geometry has been optimized by Finite Element Analysis. For sensor readout a digital measurement circuitry based on cheap standard components is developed and allows practical implementation of HCT-sensor devices for the first time. Special care has been taken in order to compensate for the temperature effects.