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Abstract: 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 005 pH in 24 h). The electric insulation was perfect when soaked in buffer solutions for more than 3 months. A continuousin 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.

Abstract: A system for the online, simultaneous and intermittent analysis of blood pH, pCO2 pO2 using two-way cyclic pumping of lactate Ringer as a baseline solution is described. The multi-gas sensor is composed of a pH-ISFET with a temperature sensor, a pH-ISFET-based pCO2 sensor and a Clark-type pO2 sensor, bundled in an epoxy rod, and held in place in a flow cell which is directly connectable to an indwelling cannula. The system is controlled by a microcomputer, which supervises pump operation, temperature-compensation of sensor outputs, one-point calibration using sampled blood analysis, and provides graphical display of monitored results. Results of arterial blood-gas monitoring for mongrel dogs are presented which demonstrate the reliability of the present system over extended periods.