Continuous oxygen monitoring in subcutaneous adipose tissue using microdialysis

A measurement system, consisting of an optochemical glass capillary oxygen sensor, an optoelectronic measuring unit and a microdialysis catheter (CMA 60) for the extraction of the biological fluid from the subcutaneous adipose tissue of critically ill patients is reported. The capillary sensor is based on the oxygen sensitive dye platinum (II) meso-tetra(pentafluorophenyl) porphyrin (Pt-TFPP) incorporated in a polystyrene matrix. The measuring system has been tested in vitro and in vivo. In particular in vitro long-term stability of the sensor has been investigated in different measurement media (elomel, 5% mannitol, Ringer, dialysed blood). The influence of different flow rates from 0.1 up to 7.0 μl min−1 on the sensor response as well as the oxygen recovery rate are discussed. The presented measurement system allows the measurement of oxygen in biological fluid in the range from 0 to 300 mmHg, with a resolution better than 1 mmHg and high accuracy (better than ±1 mmHg absolute). Finally, the suitability of the described measurement system for the continuous oxygen monitoring in subcutaneous adipose tissue has been proved in in vivo investigations performed on test animals.