Fundamental basis of tissue pH measurement

The first tissue pH electrode is described and illustrated and notable features are commented on. Calibration procedure is discussed particularly concerning the need for temperature control. Experience with early examples of the tissue electrode is described and its performance with an independent pH monitoring and recording system assessed. Attention is drawn to the fact that the electrode tip is immersed in a tissue fluid of uncertain composition and that the buffer power of the fluid must be of importance with regard to the reaction of the electrode to an acid-base disturbance. Acid-base status in man is still best described by the Henderson-Hasselbalch relationship and several features of this relationship are neglected by obstetricians intent on measuring only fetal pH. The need for careful animal experiments to determine the fundamental behaviour of the tissue pH electrode is emphasised.