Effect of location of the sensor on reflectance pulse oximetry

Abstract

Objective 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.Methods Seven healthy infants were studied between 19 and 48 hours after term delivery. Recordings of reflectance pulse oximetry were obtained from eight different sites on the infant's head. The relative changes in red to infrared light (WIR) were determined. In pulse oximetry WIR values are converted to arterial oxygen values by means of an empirically derived calibration curve.Results Significantly lower R/IR values were found at the forehead compared with the fontanelle, the parietal and occipital position, and the temporal area. Conversion to oxygen saturation values revealed a difference of up to 13.4% in oxygen saturation between the forehead and the occipital area.Conclusion 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 WIR 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 WIR 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.

Pilot investigation of anterior fontanelle photoplethysmographic signals and their suitability in estimating arterial oxygen saturation

“…Contrary to what has been reported previously [9], PPGs from the fontanelle for this pilot study were of reasonable quality to estimate SpO 2 . This warrants further trials and different setups to ascertain the optimal positioning of the sensor.…”

“…When the fontanelle is mentioned [9] the work done has been solely focused on ascertaining at what locations of the neonatal scalp would be best suited for intrapartum monitoring, that is monitoring the unborn foetus during labour, using the neonate as a direct analogue model. This study commented that although AF signals were present they suffered from an artefact that they attributed to the pulsations visibly present on the AF, and were therefore unsuitable for SpO 2 monitoring.…”

Photoplethysmographic and SpO<inf>2</inf> readings from the neonatal anterior fontanelle: A case Study

“…An earlier study looked at obtaining PPGs from the scalp of the neonate [6], and included the AF as a study site; however the results were inconclusive as they could not determine whether the PPG signals received were from the scalp or from deeper underlying tissues. It was concluded that pulsations from the sagittal sinus may have been a source of error that influenced the signals received from the scalp at the AF.…”

Development of an optoelectronic sensor for the investigation of photoplethysmographic signals from the anterior fontanel of the newborn

“…An earlier study looked at obtaining PPGs from the scalp of the neonate [6], and included the AF as a study site; however the results were inconclusive as they could not determine whether the signals received were from the scalp or from deeper underlying tissues. It was concluded that pulsations from the sagittal sinus may have been a source of error that influenced the signals received from the scalp at the AF.…”