INTRAPARTUM MEASUREMENT OF FETAL PH

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Fetal scalp blood pH as measured during labor is an important variable in assessing potential fetal distress suggested by fetal heart rate monitoring and other clinical signs. Recently developed miniature metal-metal oxide and ion sensitive field effect transistor pH sensors will be incorporated into instrumentation for the intravaginal measurement of the pH of fetal scalp blood samples and the continuous measurement of fetal scalp tissue pH. In the former case, the miniature pH transducers will be placed on a probe similar in appearance to the blood collecting pipet currently used for taking fetal scalp blood samples, so that pH of the blood specimen can be measured immediately upon drawing the sample. The advantage of this technique is the avoidance of errors associated with samples transferred to pipets and transported to the pH instrument. The proposed technique, thus, provides a pH value more rapidly. The tissue pH sensors will be constructed in a structure similar in appearance to the presently used fetal scalp electrocardiographic electrodes. This will be applied in the same way that these clinically acceptable sensors are currently used and will provide continuous pH readings. Both types of sensors will be evaluated in the laboratory in inorganic buffer and tonometered blood. The scalp sample sensor will then be evaluated on capillary blood samples from adult volunteers and infants, while the tissue sensor will be evaluated on dogs. Samples from animals will be compared with central arterial and capillary samples analyzed using routine laboratory techniques. Samples from human subjects will be measured by conventionsl laboratory means as well as the newly developed sensors. Final evaluation of both sensors will be carried out on fetuses in whom scalp blood sampling and direct fetal heart rate monitoring is clinically indicated. These clinical studies will be carried out at the Perinatal Clinical Research Center at Cleveland Metropolitan General Hospital. This center is supported by a General Clinical Research Center grant from the NIH Division of Research Resources.