Continuous tissue pH measurement in critically ill adults with a miniaturised glass electrode

A continuously reading subcutaneous pH electrode has been developed which gives relatively stable readings when applied to any well perfused part of the body. The results obtained with this electrode have been compared with the actual pH of the arterial blood measured by conventional methods. Thirty patients were studied and one hundred and sixty three observations were made. The correlation coefficient (r) between tissue pH (pHt) and arterial pH (pHa) was 0.76 (P less than 0.01). The response time of the electrode in vitro was less than one minute and, in vivo, stabilization of the recording occurred in less than three minutes. It was found that the discrepancy between pHa and pHt gave a good indication of the adequacy of tissue perfusion.