Development of a needle dislodgement detection system and a vascular access flow rate measurement system using electrical impedance

• Published in: JOURNAL OF THE KYORIN MEDICAL SOCIETY Vol. 50; no. 4; pp. 157 - 167
• Main Authors: Suda, Kenji, Kashiwagi, Tomoka, Kikuta, Masahiro, Soejima, Akinori
• Format: Journal Article
• Language: Japanese
• Published: The Kyorin Medical Society 27.12.2019
• ISSN: 0368-5829; 1349-886X
• DOI: 10.11434/kyorinmed.50.157

During hemodialysis, needle dislodgement events cause serious medical accidents and occur with a high probability. 　In recent years, for the purpose of securing adequate dialysis, high-flow-rates and highly efficient hemodialysis are becoming standard strategies. Under these conditions, needle dislodgement accidents can cause even more serious medical accidents than usual. 　However, general dialysis monitoring devices do not have a dedicated alarm for needle dislodgement, and hence, it is possible for needle dislodgement to go unnoticed. 　In this study, we developed a needle dislodgement detection system using electrical impedance values and a vascular access flow rate measurement system that uses the principle of electrical impedance. The needle dislodgement detection system utilizes the electrical impedance created in the closed circuit of the patient’s blood and dialysis line and detects needle dislodgement by opening a closed circuit at the time of needle dislodgement. We also developed a vascular access flow rate measurement system using electrical impedance based on the fact that the electrical impedance of blood when isotonic saline is injected varies according to blood flow rate during hemodialysis. 　First, we developed the oscillator and detector and the adaptor with electrodes to power the hemodialysis line. Second, we created an artificial vascular access line (a tube imitating vascular access) through which bovine blood was circulated. 　In the test of the needle dislodgement detection system, when the needle was dislodged from the artificial vascular access line, the electrical impedance value was raised, which set off an alarm. In the test of the vascular access flow rate measurement system, the vascular access flow rate varied from 100 to 600 ml/min when the dialysis machine was set in hemodialysis mode, and the blood flow rate was set to 200 ml/min. Changes in the resistivity of the bovine blood when isotonic saline was injected from the returning blood line was measured using an electrode adaptor. The results showed a strong correlation with the set vascular access flow rate and measured vascular access flow rate, with an error rate of within 20%. 　Our system worked well in a near clinical setting, although the error rate of the vascular access flow rate was large. This could be because blood reduced the change in electrical impedance value. Hence, the electrical components of our system need improvement.