Application of catheter-tip i.s.f.e.t. for continuous in vivo measurement

A catheter-tip pH sensor was developed for possible clinical and biomedical application, using an ion-sensitive field-effect transistor (i.s.f.e.t.). Its signal drift in buffer solutions during continuous measurement was less than 3 mV in 24 h (equivalent to about 0·05 pH in 24 h). The electric insulation was perfect when soaked in buffer solutions for more than 3 months. A continuous in vivo pH measurement was successfully achieved in nonheparinised arterial blood of a japanese monkey. There was no significant sign of clot formation for 8 hours. It revealed quick responses to respiratory acidosis and alkalosis, and the observed pH values were in accordance with those confirmed by a blood pH analyser. Also, a catheter-tip pCO₂ sensor was prepared, using the catheter-tip pH i.s.f.e.t. The response time was 2 min for a 90% change in CO₂ tension. The muscle pCO₂ monitoring tested with it indicated a similar result to those with medical mass spectrometer.