By Ahizechukwu C. Eke, MD, PhD, MPH
Associate Professor in Maternal Fetal Medicine, Division of Maternal Fetal Medicine, Department of Gynecology & Obstetrics, Johns Hopkins University School of Medicine, Baltimore
SYNOPSIS: This study demonstrated a statistically significant change in the use of supplemental oxygen therapy in women with category II fetal heart rate tracings in the absence of maternal hypoxia pre- and post-intervention, with no significant change in maternal or perinatal outcomes.
SOURCE: Burd JE, et al. Evaluation of an initiative to decrease the use of oxygen supplementation for category II fetal heart rate tracings. Obstet Gynecol 2021;138: 627-632.
Electronic fetal heart rate (eFHR) monitoring remains the most common obstetric procedure in the United States, with more than 80% of deliveries being monitored electronically.1 Despite its advantage in the reduction of neonatal seizures, the use of continuous eFHR monitoring has been associated with increased cesarean and assisted vaginal delivery rates with no parallel decrease in the rate of cerebral palsy.2 The inability to discern and respond to an abnormal eFHR tracing during labor is the most common cause of intrapartum stillbirths and can lead to medicolegal cases.3
In 2010, the American College of Obstetricians and Gynecologists (ACOG) developed a three-tiered classification of eFHR abnormalities and a system for interpreting these abnormalities, with category II tracings encompassing a miscellaneous group of FHR tracings that includes fetal tachycardia, marked variability, minimal variability, fetal bradycardia with variability, and no variability with absent recurrent decelerations.4 Category II eFHR tracings occur frequently and typically require frequent evaluation and correction by fetal resuscitation, including hydration, maternal repositioning, discontinuation of oxytocin and acute tocolysis (in cases of uterine hyperstimulation), and maternal supplemental oxygen administration. Despite the frequent use of maternal facial or intranasal oxygen as a method to improve fetal oxygenation in the setting of category II tracings, concerns exist of fetal cellular damage and generation of oxygen free radicals that potentially could harm the fetus.5 Because of these concerns, Thomas Jefferson University Hospital’s obstetrics and gynecology department implemented guidelines to discontinue oxygen supplementation in the setting of category II tracings in women with normal maternal oxygen saturation (≥ 95%). This study by Burd et al was undertaken to determine if healthcare providers were compliant with this guideline at Thomas Jefferson University Hospital.5
This is a quality improvement study implemented with the goal of changing the practice of routine oxygen supplementation for category II tracings on the labor and delivery unit of Thomas Jefferson University Hospital in Philadelphia. Two timeframes were studied: The first timeframe was pre-intervention (Jan. 1-March 20, 2020) and the second timeframe was post-intervention of the guideline (March 21-July 31, 2020). Inclusion criteria were women with a singleton pregnancy who presented for induction of labor or in spontaneous labor. Multiple pregnancies, pregnancies < 24 weeks’ gestation, intrauterine fetal death, fetal anomalies thought to be inconsistent with life, women with respiratory distress, and women who received oxygen supplementation for maternal desaturation ≤ 95% on room air were excluded. Patient demographics and intrapartum characteristics were collected during the study period.
The primary outcome was the number (percent) of women with normal oxygen saturation who received oxygen supplementation for category II tracings in labor before and after guideline implementation. Secondary outcome measures included the rate of cesarean delivery, both overall and for non-reassuring FHR tracings, operative deliveries (overall), operative deliveries for non-reassuring FHR tracings, frequency of Apgar scores < 7 at one and five minutes, neonatal intensive care unit admissions, and neonatal death.5
Of 1,653 women who delivered during the study period, 1,333 women met inclusion criteria (474 women in the pre-intervention group and 859 in the post-intervention group). Pre-intervention, supplemental oxygen was administered to 107 of 474 patients (22.6%). Post-intervention, oxygen was administered to five of 859 patients (0.6%); P < 0.001. Pre-intervention and post-intervention, there was no difference in any maternal or fetal outcomes.5 Neonatal deaths were secondary to perinatal infection (n = 1) and complications of placental abruption (n = 1). In multilinear regression for statistically significant demographic differences, the authors controlled for age only and for age and SARS-CoV-2-positive status, with maintenance of statistical non-significance in all secondary outcomes. All secondary outcomes were additionally calculated, excluding patients positive for SARS-CoV-2, with no statistically significant difference in maternal or fetal outcomes.
COMMENTARY
In this quality improvement study, implementation of a guideline to stop routine oxygen supplementation to normally oxygenated patients in labor was associated with excellent adherence and was not associated with an increase in adverse maternal or perinatal outcomes. Placental hypoperfusion during labor can trigger a fetal deceleration.6 In the presence of fetal hypoxia, fetal baroreceptors stimulate the parasympathetic system via vagal stimulation of the atrioventricular sinoatrial node, leading to slowing of the fetal heart rate, decreasing oxygen concentrations, and activation of chemoreceptors to further stimulate vagal/parasympathetic activity to slow the heart rate further.6,7 If the duration of the fetal deceleration is transient, the fetus is able to replenish its oxygen supply quickly. However, if decelerations are associated with marked variability, minimal variability, or no variability with absent recurrent decelerations, the tracing qualifies as category II, and requires intrauterine fetal resuscitation.
Intrauterine fetal resuscitation in the setting of a category II eFHR tracing involves hydration, maternal repositioning, discontinuation of oxytocin and acute tocolysis (in cases of uterine hyperstimulation), and maternal supplemental oxygen administration. The use of maternal oxygen as a fetal resuscitative measure (in the absence of maternal hypoxia or as pre-oxygenation prior to general anesthesia) is controversial. Studies have demonstrated that fetal compromise seen in abnormal eFHR tracings is seldom the result of maternal hypoxemia, but usually is secondary to the interference of normal utero-placental transfer of oxygen from decreased blood flow from uterine contractions on the placental circulation, placental separation/abruption, or cord compression.8,9
In addition, data demonstrate that, except when fetal hypoxia is secondary to maternal hypoxia, maternal oxygen supplementation causes an increase in free radical formation, with the potential risk of increased reperfusion and cell damage in animals and in humans.10-12 These possibilities raise concern for the routine use of maternal oxygen supplementation in the setting of category II eFHR tracings in the absence of maternal hypoxia. Although the United Kingdom’s National Institute for Health and Care Excellence guidelines recommend that maternal facial oxygen therapy should not be used for intrauterine fetal resuscitation because it may harm the baby but can be used for maternal indications, such as hypoxia or as part of preoxygenation before a potential anesthetic, ACOG supports the use of supplemental oxygen in laboring patients in the setting of category II tracings irrespective of maternal hypoxic status.
REFERENCES
- Ananth CV, et al. Electronic fetal monitoring in the United States: Temporal trends and adverse perinatal outcomes. Obstet Gynecol 2013;121:927-933.
- Alfirevic Z, et al. Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour. Cochrane Database Syst Rev 2017;2:CD006066.
- Mullins E, et al. Is continuous electronic fetal monitoring useful for all women in labour? BMJ 2017;359:j5423.
- American College of Obstetricians and Gynecologists. Practice bulletin no. 116: Management of intrapartum fetal heart rate tracings. Obstet Gynecol 2010;116:1232-1240.
- Burd JE, et al. Evaluation of an initiative to decrease the use of oxygen supplementation for category II fetal heart rate tracings. Obstet Gynecol 2021;138:627-632.
- Lear CA, et al. The myths and physiology surrounding intrapartum decelerations: The critical role of the peripheral chemoreflex. J Physiol 2016;594:4711-4725.
- Heuser CC. Physiology of fetal heart rate monitoring. Clin Obstet Gynecol 2020;63:607-615.
- Wilkening RB, et al. Fetal oxygen uptake, oxygenation, and acid-base balance as a function of uterine blood flow. Am J Physiol 1983;244:H749-755.
- Hamel MS, et al. Oxygen for intrauterine resuscitation: Of unproved benefit and potentially harmful. Am J Obstet Gynecol 2014;211:124-127.
- Kjellmer I, et al. Extracellular increase of hypoxanthine and xanthine in the cortex and basal ganglia of fetal lambs during hypoxia-ischemia. Brain Res 1989;478:241-247.
- Yamada T, et al. Effects of maternal oxygen supplementation on fetal oxygenation and lipid peroxidation following a single umbilical cord occlusion in fetal goats. J Nippon Med Sch 2003;70:165-171.
- Thorp JA, et al. Routine umbilical cord blood gas determinations? Am J Obstet Gynecol 1989;161:600-605.
This study demonstrated a statistically significant change in the use of supplemental oxygen therapy in women with category II fetal heart rate tracings in the absence of maternal hypoxia pre- and post-intervention, with no significant change in maternal or perinatal outcomes.
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