Intrapartum fetal pulse oximetry: present and future.

Pulse oximetry is widely used to monitor the patient's well-being in anesthetic and neonatal practice. As a result of recent technologic and theoretical advances, it has emerged as a clinical tool in intrapartum fetal monitoring. Oximeters record both pulse rate and arterial oxygen saturation of the fetus and they may be adapted to derive an estimate of peripheral perfusion. Reflectance oximetry is more accurate than transmission oximetry in intrapartum fetal management. This method uses the pulsatile changes of red and infrared light reflected from tissue to estimate arterial oxygenation. Pulse oximetry is cheap, non-invasive, simple to operate, relatively accurate and has a fast response time. Factors adversely affecting the accuracy of the pulse oximeter output include transducer displacement, peripheral vasoconstriction, hypotension, anemia, presence of intravascular dyes, meconium staining, fetal hair and scalp edema. Fetal pulse oximetry is limited by a wide normal range and inadequate calibration. The amniochorionic membranes however do not affect oximetry readings so that this method may be applied before rupture of the membranes, i.e. before labor. Once successfully developed, fetal pulse oximetry could potentially be used in combination with other monitoring techniques to reduce instrumental and operative interventions during labor and improve perinatal outcome.