Maternal oxygen administration and fetal well-being

LETTERS Maternal oxygen administration and fetal well-being To the Editors: The study of Thorp et al. (Thorp JA, Trobough T, Evans R, Hedrick J, Yeast JD. The effect of maternal oxygen administration during the second stage of labor on umbilical cord blood gas values: A randomized controlled prospective trial. AM J OBSTET GYNECOL 1995;172:465-74) is of interest to the Obstetric anesthesiologist. The article provides reassurance that short-term oxygen therapy may improve fetal outcome but suggests that prolonged exposure to oxygen may be associated with a deterioration in the fetal acid-base status. Unfortunately it is difficult from this study to assess the efficacy of the oxygen therapy provided by the mask to the parturient. We would not advocate measuring maternal Pao,, an uncomfortable procedure, but it is easy to record maternal saturation with a pulse oximeter. The only measure of maternal oxygenation recorded is maternal compliance in keeping the mask on, which is recorded only at 5-minute intervals. Additionally, “simple face masks” are not fixed performance devices; the concentration of oxygen delivered is affected by such variables as peak inspiratory flow and breathing pattern. Because of this, the differing forms of analgesia between the groups may be significant in determining the maternal Pao, achieved for the given fresh gas flow of 10 L/min. The two studies quoted to support the theory that maternal oxygen therapy has little beneficial effect are unfortunate choices because one demonstrates no benefit of oxygen therapy after hysterotomy, “probably because the feto-placental circulation is greatly disturbed,“’ and the second is a comparison of oxygenation with nasal prongs or face mask and no control group without oxygen was identified.” During cesarean section with the patient under general anesthesia, a situation where Fro, is well controlled and measured accurately, a maternal FIO, of 1.0 has been associated with improved fetal Pao, without an adverse effect on fetal PH.” In this study induction-to-delivery times were on average > 10 minutes and the inspired oxygen concentration was much higher than any of the mothers in the current study are likely to have received. It has also been demonstrated that 15 L of oxygen for 15 minutes during labor leads to improved fetal oxygenation as measured by infrared spectroscopy.’ In the current study the only statistically significant adverse effects on fetal acid-base status were noted between the control subgroup, with a second stage > 10 minutes, and the oxygen subgroup, with a second stage > 10 minutes (Fig. 2). This cutoff point was retrospectively made and we would welcome more information on these two subgroups to see whether they were comparable in other respects such as duration of second stage, oxytocin use, etc. It would be interesting to compare umbilical venous oxygen content in these two groups as a measure of adequacy of fetal oxygen delivery. In spite of these reservations and the questionable Q74

Snntnmher

1995

TO THE EDITORS

clinical significance of the observed changes in acidbase status, we feel that the effects of prolonged exposure of the fetus to oxygen should be explored further in a more controlled setting. T.J. Adams,

BM,

and

M. Joanne

Douglas,

MD

Dzuision of Obstetric Anaesthesia, British ColumbiaS Women’s Hospital and Health Care Society, 4490 Oak St., Vancower, British Columbia, Canada V6H 3V5 REFERENCES

Perreault C, Blaise GA, Meloche R. Maternal inspired oxygen concentration and fetal oxygenation during caesarean section. Can J Amesth 1992;39:155-7. Crosby ET, Halpern SH. Supplemental maternal oxygen therapy during caesarean section under epidural anaesthesia: a comparison of nasal prongs and face mask. Can J Anaesth 1992;39:313-6. Piggott SE, Bogod DG, Rosen M, Rees GAD, Harmer M. Isoflurane with either 100% oxygen or 50% nitrous oxide in oxygen for caesarean section. Br J Anaesth 1990;65: 325-9. Aldrich CJ, Wyatt JS, Spencer JAD, Reynolds EOR, Delpy DT. The effect of maternal oxygen administration on human fetal cerebral oxygenation measured during labour by near infra-red spectroscopy. Br J Obstet Gynaecol 1994; 101:509-13. 6/8/66770

Reply We appreciate the interest of Adams and Douglas in our research. It is unlikely that maternal oxygen saturation monitoring would have provided any useful information in our study. Most laboring pregnant women have high oxygen saturations, even on room air. Perhaps the most valuable addition to our study would have been a continuous fetal oxygen saturation monitor; however, this was not available. We used “simple face masks” because it is the standard clinical practice on labor and delivery at our institution (and most others that we are aware of). As we emphasized in our article, it is difficult if not impossible to compare previous studies because of the marked variance in the many important clinical variables. We agree that it is important for future studies to focus on the following questions regarding oxygen therapy during labor: Which fetuses (or fetal heart rate patterns) might benefit from it? What is the optimal method of administration? What is the optimal concentration? What is the optimal duration of therapy? To th,e Editors:

James Maternal-Fetal Road, Kansas

A.

Thorp,

MD,

Jane

iMedicine, Perinatal City, MO 64111

Hedrick, RN, MSN, and John D. Yeast, MD, MPH Consultants, 4400 Womall

6/8/66769

Estimation of Down syndrome risk in a donor egg pregnancy To th.e Editors: Our laboratory provides maternal serum screening for open neural tube disorders and Down syndrome. We were presented with a serum specimen American

Journal

of Obstetrics

and Gvnecoloav