Could the Cerebral Oximetry be a Good Technology to Measure Placental Oxygenation?

There is general agreement among experts to recommend the use of phenylephrine as first line therapy for the treatment of arterial hypotension induced by spinal anaesthesia during caesarean delivery. In some studies, there are trends toward a lower PaO2 values in the umbilical cord venous blood when the mother receive this vasopressor. These findings may be a result of the vasoconstrictor effect of phenylephrine on utero-placental vessels, and a subsequent increased oxygen extraction by the fetus. The possibility to extract more oxygen would provide a certain "safety margin" in the event of compromised utero-placental blood flow during normal pregnancy. However, this "safety margin" should not be taken for granted in cases where signs of fetal distress are present, and this situation might influence the choice of vasopressors.

It is well establish on a physiological basis that during labour, utero-placental blood flow is lower during the contractions. This lower blood flow could result in a lower saturation value measured by the cerebral oximeter.

Twenty patients in labour will be included in this study. Patients will be recruited in obstetric clinic during pregnancy. Based on the second trimester ultrasound, patients with anterior placenta will be included.

During labour, once a functional epidural is in place, an Invos oximeter will be install. Two sensors will be applied on the abdomen (one above the placenta and the other above the myometrium at a place without placenta). Two sensors will also be applied on the extremities (forearm and leg).Saturation values and timing of the contractions will be recorded for sixty minutes. Half of the recording will be done with an oxygen mask. Vitals signs will also be registered every five minutes.