Microfabricated needle-type sensors for in-vivo continuous monitoring of blood gas levels

In order to facilitate in vivo continuous monitoring of blood gas levels, very thin disposable pO₂, pCO₂, and pH sensors which can be incorporated in a syringe needle or a catheter were microfabricated The most critical part of the sensor was a Ag/AgCl reference electrode with a pinhole structure. Because of the structure and a novel operational mode, reproducible responses were realized for the respective sensors. Performance characterization revealed clear responses and linear calibration plots in the ranges of partial pressure or pH of physiological levels. The sensors were tolerant to ethylene oxide sterilization. The pO₂ sensor was tested by inserting it in the femoral artery of an anesthetized dog. The output of the sensor faithfully followed the changes in the pO₂ level.