THE EFFECT ON FETAL ARTERIOLAR OXYGEN-SATURATION RESULTING FROM GIVING OXYGEN TO THE MOTHER MEASURED BY PULSE OXIMETRY

Objective To determine if pulse oximetry could detect any changes in f etal arteriolar oxygen saturation resulting from maternal administrati on of oxygen. Design A prospective study comparing study comparing the fetal pulse oximetry reading before and after giving 27% and 100% oxy gen to the mother. The data were collected using an experimental pulse oximeter and a sensor specifically adapted to cope with the problems of fetal pulse oximetry. Setting Labour ward, St. James's University H ospital, Leeds University, UK. Subjects Twelve fetuses presenting by t he vertex in normal uncomplicated labour. Main outcome measures The ch ange in fetal arteriolar oxygen saturation recorded by the pulse oxime ter in response to oxygen administration to the mother. Results Twenty -seven percent oxygen increased the average fetal arteriolar oxygen sa turation by 7.5%, the effect being reversed when the oxygen was withdr awn. One hundred percent oxygen increased fetal arteriolar oxygen satu ration by 11% and when the oxygen was withdrawn oxygen saturation drop ped by 10%. One hundred percent inspired maternal oxygen was more effe ctive than 27%. The gradient of the fetal oxygen regression slope is s teeper with 100% oxygen than 27% and it is steeper when oxygen is give n compared to when it is withdrawn. This suggests that the fetus respo nds to the new placental oxygen gradient by accepting oxygen more rapi dly than it gives it up. Using a quadratic regression model, it took 9 min for fetal oxygen saturation to reach its maximum value after givi ng the mother oxygen. Conclusion This study confirms that a pulse oxim eter is able to measure an increase in fetal arteriolar oxygen saturat ion when oxygen is administered to the mother.