A study of variable decelerations in association with other heart rate patterns during monitored labor

A randomized controlled trial studying the effect of maternal hyperoxygenation on fetal heart rate in suspected fetal distress

OBJECTIVE

To investigate the effect of maternal hyperoxygenation on fetal heart rate (FHR) when applied for suspected fetal distress during the second stage of term labor.

APPROACH

A single-center randomized controlled trial was conducted in a tertiary care hospital in The Netherlands. Participants were included during the second stage of labor in case of an intermediary or abnormal FHR pattern. Patients were randomized to receive either 100% oxygen at 10 l/min until delivery, or conventional care without additional oxygen. The primary outcome was the change in FHR pattern before and after the onset of the study, measured as the change in depth and duration of FHR decelerations. Secondary outcome measures were features based on phase-rectified signal averaging (PRSA), baseline assignability, and deceleration characteristics of the FHR pattern.

MAIN RESULTS

Between March 2016 and April 2018, 117 women were included. The FHR pattern could be analyzed for 71 participants, the other 46 women delivered before the end of the post time-frame. A 2.3% reduction in depth and duration of FHR decelerations was found after maternal hyperoxygenation, compared to a 10% increase in the control group (p = 0.24). Maternal hyperoxygenation had a significantly positive effect on PRSA metrics, with a decrease in PRSA-acceleration capacity (p = 0.03) and PRSA-deceleration capacity (p = 0.02) in the intervention group compared to the control group.

SIGNIFICANCE

The difference in depth and duration of decelerations after the start of the study was not significantly different between both study groups. A statistically significant positive effect on PRSA-deceleration capacity and PRSA-acceleration capacity was found after maternal hyperoxygenation, which might be associated with a positive effect on neonatal outcome.

A prospective cohort study of fetal heart rate monitoring: deceleration area is predictive of fetal acidemia

BACKGROUND

Intrapartum electronic fetal monitoring is the most commonly used tool in obstetrics in the United States; however, which electronic fetal monitoring patterns predict acidemia remains unclear.

OBJECTIVE

This study was designed to describe the frequency of patterns seen in labor using modern nomenclature, and to test the hypothesis that visually interpreted patterns are associated with acidemia and morbidities in term infants. We further identified patterns prior to delivery, alone or in combination, predictive of acidemia and neonatal morbidity.

STUDY DESIGN

This was a prospective cohort study of 8580 women from 2010 through 2015. Patients were all consecutive women laboring at ≥37 weeks' gestation with a singleton cephalic fetus. Electronic fetal monitoring patterns during the 120 minutes prior to delivery were interpreted in 10-minute epochs. Interpretation included the category system and individual electronic fetal monitoring patterns per the Eunice Kennedy Shriver National Institute of Child Health and Human Development criteria as well as novel patterns. The primary outcome was fetal acidemia (umbilical artery pH ≤7.10); neonatal morbidities were also assessed. Final regression models for acidemia adjusted for nulliparity, pregestational diabetes, and advanced maternal age. Area under the receiver operating characteristic curves were used to assess the test characteristics of individual models for acidemia and neonatal morbidity.

RESULTS

Of 8580 women, 149 (1.7%) delivered acidemic infants. Composite neonatal morbidity was diagnosed in 757 (8.8%) neonates within the total cohort. Persistent category I, and 10-minute period of category III, were significantly associated with normal pH and acidemia, respectively. Total deceleration area was most discriminative of acidemia (area under the receiver operating characteristic curves, 0.76; 95% confidence interval, 0.72-0.80), and deceleration area with any 10 minutes of tachycardia had the greatest discriminative ability for neonatal morbidity (area under the receiver operating characteristic curves, 0.77; 95% confidence interval, 0.75-0.79). Once the threshold of deceleration area is reached the number of cesareans needed-to-be performed to potentially prevent 1 case of acidemia and morbidity is 5 and 6, respectively.

CONCLUSION

Deceleration area is the most predictive electronic fetal monitoring pattern for acidemia, and combined with tachycardia for significant risk of morbidity, from the electronic fetal monitoring patterns studied. It is important to acknowledge that this study was performed in patients delivering ≥37 weeks, which may limit the generalizability to preterm populations. We also did not use computerized analysis of the electronic fetal monitoring patterns because human visual interpretation was the basis for the Eunice Kennedy Shriver National Institute of Child Health and Human Development categories, and importantly, it is how electronic fetal monitoring is used clinically.

Intrauterine resuscitation during the second stage of term labour by maternal hyperoxygenation versus conventional care: study protocol for a randomised controlled trial (INTEREST O2)

BACKGROUND

Perinatal asphyxia is, even in developed countries, one the major causes of neonatal morbidity and mortality. Therefore, if foetal distress during labour is suspected, one should try to restore foetal oxygen levels or aim for immediate delivery. However, studies on the effect of intrauterine resuscitation during labour are scarce. We designed a randomised controlled trial to investigate the effect of maternal hyperoxygenation on the foetal condition. In this study, maternal hyperoxygenation is induced for the treatment of foetal distress during the second stage of term labour.

METHODS/DESIGN

This study is a single-centre randomised controlled trial being performed in a tertiary hospital in The Netherlands. From among cases of a suboptimal or abnormal foetal heart rate pattern during the second stage of term labour, a total of 116 patients will be randomised to the control group, where normal care is provided, or to the intervention group, where before normal care 100% oxygen is supplied to the mother by a non-rebreathing mask until delivery. The primary outcome is change in foetal heart rate pattern. Secondary outcomes are Apgar score, mode of delivery, admission to the neonatal intensive care unit and maternal side effects. In addition, blood gas values and malondialdehyde are determined in umbilical cord blood.

DISCUSSION

This study will be the first randomised controlled trial to investigate the effect of maternal hyperoxygenation for foetal distress during labour. This intervention should be recommended only as a treatment for intrapartum foetal distress, when improvement of the foetal condition is likely and outweighs maternal and neonatal side effects.

TRIAL REGISTRATION

EudraCT, 2015-001654-15; registered on 3 April 2015. Dutch Trial Register, NTR5461; registered on 20 October 2015.

Accelerated acidosis in response to variable fetal heart rate decelerations in chronically hypoxic ovine fetuses

BACKGROUND

Due to limitations of technology, clinicians are typically unable to determine if human fetuses are normoxic or moderately, chronically hypoxic. Risk factors for chronic hypoxia include fetal growth restriction, which is associated with an increased incidence of oligohydramnios and thus a risk for umbilical cord occlusion (UCO) and variable fetal heart rate (FHR) decelerations. At delivery, fetal growth restriction infants (<3rd percentile) have nearly twice the incidence of low Apgar scores and umbilical pH <7.0. Despite the risks of oligohydramnios and intermittent UCO, there is little understanding of the acid/base responses rates of chronically hypoxic fetuses to variable FHR decelerations as might occur during human labor.

OBJECTIVE

We sought to compare the increase in base deficit (BD) among chronically hypoxic as compared to normoxic ovine fetuses in response to simulated mild, moderate, and severe variable FHR decelerations.

STUDY DESIGN

Near-term ovine fetuses were chronically prepared with brachial artery catheters and an inflatable umbilical cuff occluder. Following a recovery period, normoxic (n = 9) and spontaneously hypoxic (n = 5) fetuses were identified (arterial O2 saturation ≤55%). Both animal groups underwent graded, 1-minute occlusions every 2.5 minutes with 1 hour of mild (∼30 beats/min [bpm] decrease from baseline), 1 hour of moderate (∼60 bpm decrease from baseline), and up to 2 hours of severe (∼90 bpm decrease from baseline) variable FHR decelerations until fetal arterial pH reached 7.00, when occlusions were stopped.

RESULTS

Repetitive UCO resulted in development of acidosis (pH <7.0) in both groups. Hypoxic and normoxic fetuses demonstrated similar BD increases in response to both mild (0.39, interquartile range [IQR] 0.28-0.45 vs 0.26, IQR 0.01-0.30 mEq/L/10 min, P = .25) and severe (1.97, IQR 1.50-2.43 vs 1.51, IQR 0.97-2.45 mEq/L/10 min, P = .63) variable decelerations. However, moderate variable decelerations increased BD in hypoxic fetuses at 2.5 times the rate of normoxic fetuses (0.97, IQR 0.52-1.72 vs 0.39, IQR 0.23-0.47 mEq/L/10 min, P = .03). During the recovery period, hypoxic fetuses cleared BD slower than normoxic fetuses (0.08 ± 0.02 vs 0.12 ± 0.03 mEq/L/min, P = .02).

CONCLUSION

In comparison to normoxic fetuses, hypoxic fetuses can more rapidly progress to significant metabolic acidosis in response to moderate FHR variable decelerations, and more slowly recover with in utero resuscitation, likely a consequence of impaired placental function and fetal physiologic responses.

[Fetal heart rate during labour: definitions and interpretation]

Continuous fetal heart rate monitoring is widely used during labor even in low risk pregnancies. Consensus is necessary to define and interpret accurately the different FHR patterns. The normal FHR tracing include baseline rate between 110-160 beats per minute (bpm), moderate variability (6-25 bpm), presence of accelerations and no decelerations. Uterine activity is monitored simultaneously: contractions frequency, duration, amplitude and relaxation time must be also normal. Abnormal baseline heart rate during 10 minutes or more is termed tachycardia above 160 bpm (except for FIGO above 150) and bradycardia below 110 bpm. Variability is minimal below 6 bpm and absent when non visible. Decelerations are classified as early, variable, late, and prolonged. Early and late decelerations have an onset gradual decrease of FHR, in contrast variable decelerations have an abrupt onset. Early deceleration is coincident in timing with uterine contraction. Variable deceleration is variable in onset, duration and timing, and may be described as typical or non reassuring. Late deceleration is associated with uterine contraction; the onset, nadir, and recovery occur after onset, peak and end of the contraction. Prolonged deceleration is lasting more than two but less 10 minutes, with almost onset abrupt and no repetition. Electronic fetal monitoring is a method to detect risk of fetal asphyxia; analysis and interpretation of FHR patterns are difficult with a high false positive rate, increasing operative deliveries. The patterns who are predictive of severe fetal acidosis include recurrent late or variable or prolonged decelerations or bradycardia, with absent FHR variability, and sudden severe bradycardia. The other FHR patterns are not conclusive and defined as non reassuring; obstetrical risk factors must be considered and other method (like scalp sampling for pH) utilised to evaluate fetal state.

Power spectral analysis of heart rate variability during acute hypoxia in fetal lambs

BACKGROUND

The aim of the current study was to investigate the changes in the power spectral pattern of the heart rate variability of fetal lambs during acute hypoxia and the possible value of power spectral analysis as a quantitative fetal monitoring method.

METHODS

Acutely instrumented eight fetal lambs in the third trimester of gestation were subjected to reproducible hypoxia by reducing the maternal placental blood flow with complete obstruction of the maternal abdominal aorta for 60 s. Fetal electrocardiographic data 5 min prior to occlusion, 1 min during occlusion and 1, 5, and 10 min after the removal of occlusion were analyzed using power spectral analysis. Differences among the procedural steps were determined by the Friedman test with multiple comparisons using Duncan's multiple-range test. Wilcoxon's rank sum test was used for the comparison between low-and high-frequency power values at each step. p< 0.05 was considered significant.

RESULTS

Low-, high-, total-frequency power and low-to-high frequency ratio all significantly increased with hypoxia compared with the baseline state (p < 0.05). High-frequency power remained higher than low-frequency power during the resting state (baseline state, 5 and 10 min after hypoxia).

CONCLUSIONS

Increased low-frequency power and low-to-high frequency ratio during hypoxia reflects increased sympathetic activity compared with the baseline state. Higher high-frequency power during the resting state compared with low-frequency power reflects active respiratory movement of the fetal lambs near term and increased parasympathetic activity. It appeared possible that power spectral analysis could serve as a useful quantitative tool to monitor the autonomic changes in fetal lambs during hypoxia.

Perinatal asphyxia: assessing its causal role and timing

Perinatal asphyxia, whether prenatal, intrapartum, or neonatal is thought to be a significant contributor to newborn morbidity and mortality as well as long-term neurological deficits. Development of an intrapartum tool/test that can reliably identify and discriminate between varying degrees of fetal acidemia and suggest whether it is respiratory or metabolic in nature would be highly desirable. This article critically reviews the available experience with the currently available monitoring techniques and the significance of abnormalities of fetal and intrapartum measurements with respect to the predictive value of the observations available to the clinician.

The accuracy of auscultatory detection of fetal cardiac decelerations: a computer simulation

To evaluate current practices of auscultation for the detection of decelerations, we used a computer to generate contractions and late decelerations and perform the counting. The baseline rate ranged from 110 to 180 beats/min. The duration of the deceleration ranged from 1 to 2 minutes, and the amplitude of the deceleration ranged from 10 to 90 beats/min. The onset of the decelerations ranged from 0.4 to 0.7 of the length of the contraction. Counting was begun at 80%, 100%, and 120% of the contraction length. The duration of counting varied between 15 and 60 seconds. A multicount algorithm obtained three 10-second counts separated by 5 seconds. Results were classified by the ability to detect rates below 120, 100, or 80 beats/min (threshold determination) or 20 and 25 beats/min below the baseline rate (subtraction determination). The baseline rate and deceleration amplitude had the greatest effect on accuracy. The higher the baseline rate and the smaller the deceleration amplitude, the less accurate was detection. Multiple counts were more accurate than the single-count strategy, and subtraction detection was more accurate than threshold detection. The effects of counting error are briefly described. This model, which requires clinical confirmation, nevertheless emphasizes the potential inaccuracies of many popular schemes of auscultatory surveillance, even for the detection of prolonged or sustained decelerations. Certain modifications of auscultatory practice may improve the accuracy of this technique.

Evaluation of variable decelerations of fetal heart rate with the deceleration index: influence of associated abnormal parameters and their relation to the state and evolution of the newborn

The deceleration index of the Fetal heart rate (FHR) (Acién P. et al. (1979) J. Perinat Med 7, 7-18) was used to analyze 157 cardiotocographic registers that displayed variable deceleration during labor. We have related the deceleration index value to perinatal results and to other abnormal parameters of FHR. An increase in neonatal pathology was observed in the deceleration group compared to a group of 50 controls with normal FHR, when the deceleration index was greater than 150 and specially if it was greater than 200. The association of other abnormal parameters of FHR (especially absence of variability between or during decelerations, absence of transitory ascents, presence of tachycardia and, of less importance, absence of ascents at the beginning of deceleration or presence of overshoot acceleration following deceleration) yields a worse prognosis for the fetus than does an increased deceleration index alone. The deceleration index is a good method for evaluation of variable decelerations of FHR, and is well correlated to the condition of the newborn.