Artifacts in fetal pulse oximetry: nonarterial pulsatile signals

We wished to investigate the effect of caput succedaneum on pulse oximetry readings.

Oxygen saturation was measured by reflection pulse oximetry on various sites of scalps of 18 healthy neonates. The pulse rate obtained from the oximeter was checked against the heart rate from the electrocardiogram to see whether they were in agreement and synchronized.

Nonsynchronized saturation values had a much wider range (30 to 97 vs 70 to 98) and a significantly lower mean (70 vs 84) than did synchronized values. Synchronized readings were obtainable in all 18 subjects over the temporal region but in only 39% of cases over the occipital region. Fourteen neonates had caput succedaneum, and in nine (61%) of these synchronized readings were not possible. It was noted that falsely low saturation values can be derived from pulsating waveforms, which have a slower rate than the electrocardiogram rate.

The observed low pulsation rate is either of venous origin or represents modulated transmission of arterial signal through an edematous or congested scalp. This artifact will result in nonarterial oxygen saturation readings, and its exclusion is of importance in the development of pulse oximetry for intrapartum monitoring of the fetus.