Fetal oximetry and acidosis

Abstract

Fetal pulse oximetry allows oxygen saturation to be monitored during labour (1,3,4). We have found (3) that a prolonged drop in baseline saturation is associated with acidosis and fetal distress. This could be explained by the Bohr shift, i.e. a right shift of the oxygen dissociation curve resulting in a lower saturation level even when the oxygen tension is maintained at normal levels (Fig. 1). We set out to quantify in vitro the effect that pH can have on oxygen saturation levels in fetal blood and to analyse the implications of such changes for intrapartum monitoring with pulse oximetry.