An evaluation of the continuous tissue pH electrode (tpH) during labor in the human fetus.

The subcutaneous tissue pH (tpH) of 31 fetuses has been measured continuously during labor using the tissue electrode designed by Stamm and adapted for fetal use by ROCHE Medical and Laboratory Systems. There were seven failures, 16 reliable readings, and eight erratic and low readings. Comparison of the reliable tpH readings with scalp capillary blood pH showed a correlation coefficient of 0.64 (p less than 0.001). Comparison of the last intrapartum tissue pH value and cord arterial blood pH showed a correlation coefficient of 0.86 (p less than 0.001). Difficulty in application of the electrode to the fetal scalp appears to be the biggest problem and this is also responsible for unreliable readings. Technical improvements and a substantial increase in the number of the available electrodes and accessory instruments are necessary before this procedure becomes a routine clinical tool in the delivery suite.