A Study of Micro-shock Hazard in EMIS-Based pH Sensor During Fetal Acidosis Assessment

Fetal acidosis assessment is crucial during labor. Diagnosis of fetal acidosis will help to strengthen decision for c-section delivery in fetal with oxygen deficiency where pH ≤ 7.20 or SpO2 ≤ 35%. This can be determined using electromagnetic induction spectroscopy technique (EMIS) where it has a bright future to be implemented as a non-invasive fetal monitoring device for fetal acidosis assessment. The development of EMIS pH sensor is important in order to replace the existing invasive fetal blood sampling (FBS) which introduced hazards to the fetus. However, there is still lack of research associated with this application. Here, we present the simulation study of micro-shock in EMIS pH sensor using COMSOL Multiphysics. In EMIS application, the excitation current must be enough to induce current in low conductivity fetal scalp, at the same time harmless to the fetus. Therefore, a transmitter coil with current value of 1 and 10 μA and frequency 1–10 MHz has been tested on 8 cm spherical fetal head model at 6 different depths. The result shows at 6–10 MHz, the induced current density in the fetal scalp is always higher compared to the excitation current. While micro-shock could occur with excitation of 10 μA, 10 MHz at Point 2 located 2 mm below the fetal scalp surface. Hence, 1 μA was selected as the best excitation current with excitation frequency range 1–5 MHz. It has produced μV range induced voltage at the receiver which can be further converted to pH values.