Continuous in vivo monitoring in diabetes: the subcutaneous glucose concentration

The most advanced glucose sensors are measuring amperometrically the hydrogen peroxide generated in a stoichiometric relation to the prevailing glucose concentration during glucose oxidase-mediated glucose oxidation. They proved useful in commercially available glucose analysers and in experimental subcutaneous (sc) monitoring. Here it is shown (a) that under steady state conditions the s.c glucose concentration is nearly identical to that in blood, (b) that sc. inserted glucose electrodes do mirror the intracorporal glucose concentration both under hypo-, normo-, and hyperglycaemic conditions with a clinically relevant accuracy, (c) that automated feedback control of intracorporal glucose concentration is possible applying the output of sc. glucose sensor as an input to the computer that controls the insulin pump, and (d) that stable function of sc. sensor may be accomplished over intervals up to one day; in some cases applications over up to ten days have been reported. The underlying problem consists in an insufficient functional biostability which is a function of biocompatibility and size of the sensor, of its sterility, and of the permanent skin penetration. The latter is still required to get the device in place, to keep it in function, and to make use of the data under any condition. At this time, sc. glucose electrodes to be employed as hypoglycaemia-warning systems over one day are considered clinically important and technically achievable.