British journal of obstetrics and gynaecology
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The influence of the location of the sensor on reflectance pulse oximetry during fetal monitoring in labour was investigated using the newborn infant as a model. ⋯ Assuming that the arterial blood oxygen saturation did not change substantially, our findings indicate that in reflectance pulse oximetry there is no unique relation between R/IR and arterial oxygen saturation. The differences in reflectance pulse oximetry at the various sites are explained by differences in optical properties (scattering and absorption) of the tissue underneath the sensor. These will affect the red and infrared light reaching the detectors in a different way, and consequently R/IR changes. Because during intrapartum monitoring exact positioning of the sensor on the fetal head is usually impossible, the accuracy of fetal reflectance pulse oximetry is impaired.