Intrapartum fetal pulse oximetry: Past, present, and future,☆☆,

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Abstract

Oxygen saturation monitoring (pulse oximetry) has markedly improved medical care in many fields, including anesthesiology, critical care, and newborn intensive care. In obstetrics, fetal heart rate monitoring remains the standard for intrapartum assessment of fetal well-being. Fetal heart rate monitoring is sensitive but nonspecific for detecting fetal compromise. Additional clinical information is needed to discern those fetuses not at risk for development of intrapartum acidosis to avoid unnecessary intervention. Fetal oxygen saturation monitoring is a new technique currently under development. This article reviews the evolution of intrapartum fetal oxygen saturation monitoring and proposes directions for future investigation. (Am J Obstet Gynecol 1996;175:1-9.)

Section snippets

BRIEF HISTORY OF PULSE OXIMETRY

Pulse oximetry, simply stated, measures the ratio of oxyhemoglobin concentration (O2Hb) to the sum of oxyhemoglobin and reduced hemoglobin (Hb) in blood.

With this formula only hemoglobin forms capable of reversibly binding oxygen are measured; dysfunctional forms such as carboxyhemoglobin and methemoglobin are not included in the calculation. In most clinical circumstances these dysfunctional forms of hemoglobin constitute an insignificantly small proportion of total hemoglobin.

Oximetry was

DEVELOPMENT OF FETAL PULSE OXIMETRY: CORRELATION IN ANIMALS

Because access to the human fetal preductal arterial circulation is not feasible, attempts have been made to calibrate fetal pulse oximeters with the use of laboratory animals. Table I summarizes such published studies. Fetal Sao2 is varied by controlling maternal Fio2 or uterine blood flow. Linear regression and correlation analysis is usually used to evaluate the relationship between Sao2 and Spo2, with limits of agreement defined by some measure (standard deviation or standard error)

DEVELOPMENT OF FETAL PULSE OXIMETRY: HUMAN SUBJECTS

Pulse oximeters designed for use in the child after birth or in the adult are of the transmission type, where light-emitting diodes shine light through a tissue bed; a photodetector on the opposite side of the tissue bed detects light not absorbed by the tissues. The fetus in utero does not have an exposed area that would allow placement of a transmission sensor. Thus reflectance sensors have been designed, whereby the light-emitting diodes are located adjacent to the photodetector (Fig. 2).

FUTURE DIRECTION OF INTRAPARTUM FETAL PULSE OXIMETRY

Ideally, fetal pulse oximeters should be calibrated in human fetuses by simultaneous measurement of Spo2 and preductal Sao2. However, access to the fetal preductal circulation in utero during labor is not feasible. Calibration studies on adult human subjects with Spo2 values < 60% are not practical because of safety and ethical issues. Studies have been performed to correlate preductal Spo2 with umbilical cord blood Sao2; however, the preductal Sao2 theoretically lies somewhere between

COMMENT

Technical advances in acid-base monitoring have revolutionized the practice of medicine in fields such as anesthesia, critical care, and neonatal intensive care. Obstetricians have not seen many significant changes in intrapartum fetal assessment since the introduction of FHR monitoring and scalp blood gas analysis 30 years ago and strongly desire new technology to aid in fetal evaluation.

Intrapartum fetal oxygen saturation monitoring is an emerging research tool that has potential for clinical

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    From the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Utah School of Medicine,a and the Intermountain Health Care Perinatal Centers, LDS Hospital.b

    ☆☆

    Reprint requests: Gary A. Dildy, MD, Perinatal Center, Utah Valley Regional Medical Center, 1034 North 500 West, Provo, UT 84604.

    0002-9378/96 $5.00 + 0 6/1/69801

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