Determination of the electrical conductivity of biological fluids using glucose sensors

Objective: New insulin analogues used to treat patients with diabetes must be tested in clinical clamp studies. Automated clamp devices could reduce the costs of these labour- intensive manual clamps. Intravenous microdialysis (ivMD) has become an attractive approach for continuous glucose monitoring (CGM); however, fluctuations in recovery limit its usefulness. It has been shown in previous studies that such fluctuations in glucose recovery can be partly compensated by using the Ionic Reference Technique (IRT). Our objective was to investigate whether CGM using ivMD can be improved by measuring the conductivity online, over the sensor electrodes, enabling the IRT.

Methods: The CGM comprises the CMA64 ivMD, Dexcom STS 7, flow through cell and Gamry potentiostat. The system was first in vitro characterized and then tested in a clinical study in 5 diabetic volunteers over 24h. An antithrombotic drug was used to minimise clotting of the MD membranes. Blood glucose was clamped to four target levels for 6 hours. Dialysate was analysed offline and online for glucose and ions and rated applying a regression analysis.

Results: Measurement of glucose and conductivity could be established in vitro in a reliable and reproducible manner. In contrast, data of in vivo investigations showed a weak correlation for glucose signals obtained with the online sensor and no correlation for the conductivity measurement.

Conclusion: We showed that online glucose- and conductivity measurement can be established using the same sensor electrodes to enable the application of the IRT. Nevertheless, the system needs substantial improvement to be ready for in vivo use.