Combination of microdialysis and glucose sensor for continuous on line measurement of the subcutaneous glucose concentration: theory and practical application.

The microdialysis technique can be used to get dialysates of the subcutaneous tissue, which can be continuously measured by an amperometric glucose sensor. In order to get further insight into the microdialysis procedure, we used a steady-state theory for microdialysis to predict the recovery of glucose in the dialysate and compared the results to experimental data obtained by a combination of the microdialysis technique with continuous amperometric glucose sensing. The recovery of glucose obtained in vitro for two different microdialysis probes was close to the theoretical predictions. When quantifying the predictions of the model with regard to the spatial concentration profile in the subcutaneous tissue, it appeared, that the presence of the microdialysis probe depressed the concentration of glucose for 0.2 mm from the probe surface. In a 24 hour in vivo experiment, there were less fluctuations in the sensor signal when the patient was lying in bed compared to the time, when the patient could move freely. In conclusion, the combination of microdialysis and glucose sensor seems to be a promising approach to a continuously functioning glucose sensing system. However, the microdialysis procedure itself disturbs the surrounding of the probe leading to a concentration gradient of glucose. This might explain some differences between the course of blood glucose and the course of subcutaneous glucose, measured by the combination of microdialysis and an amperometric glucose sensor. Further developments of such systems should aim at implanting microdialysis devices which have a minimal influence upon the tissue metabolism.