The Effect of Maternal Oxygen Administration on Fetal Pulse Oximetry During Labor in Fetuses with Nonreassuring Fetal Heart Rate Patterns

Abstract & Commentary

By John C. Hobbins, MD, Professor and Chief of Obstetrics, University of Colorado Health Sciences Center, Denver. Dr. Hobbins reports no financial relationship relevant to this field of study.
This article originally appeared in the November 2006 issue of OB/GYN Clinical Alert. It was edited by Leon Speroff, MD, and peer reviewed by Catherine LeClair, MD. Dr. Speroff is Professor of Obstetrics and Gynecology, Oregon Health and Science University, Portland, and Dr. LeClair is Assistant Professor, Department of OB/GYN, Oregon Health and Science University. Dr. Speroff is a consultant for Barr Laboratories, and does research for Wyeth. Dr. LeClair reports no financial relationship relevant to this field of study.

Synopsis: The administration of supplemental oxygen to laboring patients with nonreassuring fetal heart rate patterns increases fetal oxygen saturation substantially and significantly. Fetuses with the lowest initial oxygen saturations appear to increase the most.

Source: Haydon ML, et al. The effect of maternal oxygen administration on fetal pulse oximetry during labor in fetuses with nonreassuring fetal heart rate patterns. Am J Obstet Gynecol. 2006;195:735-738.

For years clinicians have been administering oxygen by mask to patients with worrisome fetal heart rate patterns. Yet, a Cochrane database review has questioned this practice because of the lack of solid date to demonstrate its benefit.1

A group from University of California-Irvine set out to see if oxygen by mask could boost the fetal oxygen saturation in those fetuses that might actually need extra oxygen—those with nonreassuring fetal heart rate patterns in labor. Twenty-four women in labor were recruited to participate in the study. Each had fetuses who demonstrated combinations of decreased beat-to-beat variability with tachycardia and/or late decelerations. After baseline values at room air were obtained, the patients were given 40% by simple face mask and later (after a washout time of 30 minutes), 100% fraction of inspired oxygen (FIO2) by nonrebreathing mask. The fetal oxygen saturation was determined continuously by a pulse oximeter applied to the fetal cheek.

The study resulted in the following findings:

  • In those with normal O2 saturation (>50%), there was little change after maternal oxygen administration.
  • In those fetuses with low values initially there was, on average, a 5% increase in baseline O2 saturation with 40% FIO2 and a 6.5% rise with 100% FIO2.
  • The nine fetuses with the lowest baseline O2 saturation (< 40%) had the largest rise, 7.0% with 40% administered FIO2 and 12.6% after 100% FIO2.

Commentary

This study only concentrated on the population of fetuses who might need O2 the most—those with evidence of non-reassuring fetal heart rate tracings, many of whom had low O2 saturation. To me, here was a clear demonstration that O2 by mask can work in raising the O2 saturation in fetuses showing evidence of "fetal distress"—now a term that is no longer politically correct. However, we need to be very selective in using O2 by mask. First, it is confusing and downright annoying for a patient that wants to, and needs to, move around and even ambulate. Second, it is anxiety provoking in many already fearful patients by indirectly indicating their fetuses may be in trouble.

Unfortunately, while we continue to interdict patients from having food or drink in labor, we liberally hand out O2 masks to anyone in labor who looks at us cross-eyed. Also, O2 saturation monitoring investigation has shown that patients whose fetuses demonstrate moderate to severe variable decelerations, a very common occurrence that triggers O2 by mask in virtually every hospital in the country, will have no drop in their O2 saturation during these episodes.

O2 saturation monitors have fallen out of favor because studies involving large numbers have not demonstrated an improved benefit in outcome when it is used. However, here is an example of how investigation that would not be otherwise possible has demonstrated something that many have wondered about for years: Does maternal O2 delivery by mask really improve O2 saturation in the fetus? This study says "yes" but only in those who might really need it.

Now, whether this translates out into an improved outcome may have to await further study. However, let's narrow down its use to only those at highest risk for fetal compromise and leave the others alone.

Reference

1. Fawole B, Hofmeyr GJ. Maternal oxygen administration for fetal distress. Cochrane Database Syst Rev. 2003;(4):CD000136.