Development of a conductometric biocompatible sensor for detecting ischemia

Insufficient blood supply to the organs is the major cause of morbidity and mortality worldwide. This condition must be detected early to avoid irreversible loss of function and tissue death as occurs with for instance myocardial infarction, stroke and many other diseases. It has been shown that CO₂ tension in tissue is a valid variable for detecting insufficient blood supply in any organ, yet there exists no commercially available sensor capable of performing this measurement continuously, selectively and in real-time. In this paper we present a sensor prototype for measuring tissue tension of CO₂ (PCO₂) based on a conductometric principle. It has a diameter of 1mm, and is made purely of biocompatible materials. The sensor has been produced by injection moulding, laser patterning, electroplating and manual assembly. Its challenges of drift and long-time survivability are discussed. We will also discuss optimisation of electrode polarisation and stray capacitance of miniaturised electrodes, challenges that are relevant also for a larger span of miniaturised devices. We describe different in vivo experiments where the sensor has shown a lack of blood supply in several types of tissues with high sensitivity and specificity. It is expected that this approach will help to save the lives of patients and in the future become part of the standard of organ monitoring.