The effect of meconium on neonatal and fetal reflectance pulse oximetry.

Reflectance probes are being developed for neonatal use and obstetricians are beginning to use reflectance pulse oximetry to monitor the fetus. When a reflectance probe was used to monitor the arterial oxygen saturation of a baby whose skin was stained with meconium an artificially low result was obtained. This is because meconium absorbs more red than infra-red light and acts as a red light filter between the vascular bed and the probe. This effect may be reproduced by interposing a red filter between a reflectance pulse oximetry probe and the skin. Obstetricians who use a pulse oximeter to assess the fetus through intact membranes will record an erroneously low result if they are stained with meconium. Similarly neonatologists should avoid placing a reflectance pulse oximetry probe on babies skin which is stained with meconium.