Real-time spectral analysis of the fetal EEG: a new approach to monitoring sleep states and fetal condition during labor

Not with a “zap” but with a “beep”: measuring the origins of perinatal experience

When does the mind begin? Infant psychology is mysterious in part because we cannot remember our first months of life, nor can we directly communicate with infants. Even more speculative is the possibility of mental life prior to birth. The question of when consciousness, or subjective experience, begins in human development thus remains incompletely answered, though boundaries can be set using current knowledge from developmental neurobiology and recent investigations of the perinatal brain. Here, we offer our perspective on how the development of a sensory perturbational complexity index (sPCI) based on auditory ("beep-and-zip"), visual ("flash-and-zip"), or even olfactory ("sniff-and-zip") cortical perturbations in place of electromagnetic perturbations ("zap-and-zip") might be used to address this question. First, we discuss recent studies of perinatal cognition and consciousness using techniques such as functional magnetic resonance imaging (fMRI), electroencephalography (EEG), and, in particular, magnetoencephalography (MEG). While newborn infants are the archetypal subjects for studying early human development, researchers may also benefit from fetal studies, as the womb is, in many respects, a more controlled environment than the cradle. The earliest possible timepoint when subjective experience might begin is likely the establishment of thalamocortical connectivity at 26 weeks gestation, as the thalamocortical system is necessary for consciousness according to most theoretical frameworks. To infer at what age and in which behavioral states consciousness might emerge following the initiation of thalamocortical pathways, we advocate for the development of the sPCI and similar techniques, based on EEG, MEG, and fMRI, to estimate the perinatal brain's state of consciousness.

Current and Future Uses of Continuous EEG in the NICU

Continuous EEG (cEEG) is a fundamental neurodiagnostic tool in the care of critically ill neonates and is increasingly recommended. cEEG enhances prognostication via assessment of the background brain activity, plays a role in predicting which neonates are at risk for seizures when combined with clinical factors, and allows for accurate diagnosis and management of neonatal seizures. Continuous EEG is the gold standard method for diagnosis of neonatal seizures and should be used for detection of seizures in high-risk clinical conditions, differential diagnosis of paroxysmal events, and assessment of response to treatment. High costs associated with cEEG are a limiting factor in its widespread implementation. Centralized remote cEEG interpretation, automated seizure detection, and pre-natal EEG are potential future applications of this neurodiagnostic tool.

Monitoring Fetal Electroencephalogram Intrapartum: A Systematic Literature Review

Background: Studies about the feasibility of monitoring fetal electroencephalogram (fEEG) during labor began in the early 1940s. By the 1970s, clear diagnostic and prognostic benefits from intrapartum fEEG monitoring were reported, but until today, this monitoring technology has remained a curiosity. Objectives: Our goal was to review the studies reporting the use of fEEG including the insights from interpreting fEEG patterns in response to uterine contractions during labor. We also used the most relevant information gathered from clinical studies to provide recommendations for enrollment in the unique environment of a labor and delivery unit. Data Sources: PubMed. Eligibility Criteria: The search strategy was: ("fetus"[MeSH Terms] OR "fetus"[All Fields] OR "fetal"[All Fields]) AND ("electroencephalography"[MeSH Terms] OR "electroencephalography"[All Fields] OR "eeg"[All Fields]) AND (Clinical Trial[ptyp] AND "humans"[MeSH Terms]). Because the landscape of fEEG research has been international, we included studies in English, French, German, and Russian. Results: From 256 screened studies, 40 studies were ultimately included in the qualitative analysis. We summarize and report features of fEEG which clearly show its potential to act as a direct biomarker of fetal brain health during delivery, ancillary to fetal heart rate monitoring. However, clinical prospective studies are needed to further establish the utility of fEEG monitoring intrapartum. We identified clinical study designs likely to succeed in bringing this intrapartum monitoring modality to the bedside. Limitations: Despite 80 years of studies in clinical cohorts and animal models, the field of research on intrapartum fEEG is still nascent and shows great promise to augment the currently practiced electronic fetal monitoring. Prospero Number: CRD42020147474.

Computer-based intrapartum fetal monitoring and beyond: A review of the 2nd Workshop on Signal Processing and Monitoring in Labor (October 2017, Oxford, UK)

The second Signal Processing and Monitoring in Labor workshop gathered researchers who utilize promising new research strategies and initiatives to tackle the challenges of intrapartum fetal monitoring. The workshop included a series of lectures and discussions focusing on: new algorithms and techniques for cardiotocogoraphy (CTG) and electrocardiogram acquisition and analyses; the results of a CTG evaluation challenge comparing state-of-the-art computerized methods and visual interpretation for the detection of arterial cord pH <7.05 at birth; the lack of consensus about the role of intrapartum acidemia in the etiology of fetal brain injury; the differences between methods for CTG analysis "mimicking" expert clinicians and those derived from "data-driven" analyses; a critical review of the results from two randomized controlled trials testing the former in clinical practice; and relevant insights from modern physiology-based studies. We concluded that the automated algorithms performed comparably to each other and to clinical assessment of the CTG. However, the sensitivity and specificity urgently need to be improved (both computerized and visual assessment). Data-driven CTG evaluation requires further work with large multicenter datasets based on well-defined labor outcomes. And before first tests in the clinic, there are important lessons to be learnt from clinical trials that tested automated algorithms mimicking expert CTG interpretation. In addition, transabdominal fetal electrocardiogram monitoring provides reliable CTG traces and variability estimates; and fetal electrocardiogram waveform analysis is subject to promising new research. There is a clear need for close collaboration between computing and clinical experts. We believe that progress will be possible with multidisciplinary collaborative research.

Lost in Transition: A Systematic Review of Neonatal Electroencephalography in the Delivery Room-Are We Forgetting an Important Biomarker for Newborn Brain Health?

BACKGROUND

Electroencephalography (EEG) monitoring is routine in neonatal intensive care units (NICUs) for detection of seizures, neurological monitoring of infants following perinatal asphyxia, and increasingly, following preterm delivery. EEG monitoring is not routinely commenced in the delivery room (DR).

OBJECTIVES

To determine the feasibility of recording neonatal EEG in the DR, and to assess its usefulness as a marker of neurological well-being during immediate newborn transition.

METHODS

We performed a systematic stepwise search of PubMed using the following terms: infant, newborns, neonate, DR, afterbirth, transition, and EEG. Only human studies describing EEG monitoring in the first 15 min following delivery were included. Infants of all gestational ages were included.

RESULTS

Two original studies were identified that described EEG monitoring of newborn infants within the DR. Both prospective observational studies used amplitude-integrated EEG (aEEG) monitoring and found it feasible in infants >34 weeks' gestation; however, technical challenges made it difficult to obtain continuous reliable data. Different EEG patterns were identified in uncompromised newborns and those requiring resuscitation.

CONCLUSION

EEG monitoring is possible in the DR and may provide an objective baseline measure of neurological function. Further feasibility studies are required to overcome technical challenges in the DR, but these challenges are not insurmountable with modern technology.

Adaptive shut-down of EEG activity predicts critical acidemia in the near-term ovine fetus

In fetal sheep, the electrocorticogram (ECOG) recorded directly from the cortex during repetitive heart rate (FHR) decelerations induced by umbilical cord occlusions (UCO) predictably correlates with worsening hypoxic-acidemia. In human fetal monitoring during labor, the equivalent electroencephalogram (EEG) can be recorded noninvasively from the scalp. We tested the hypothesis that combined fetal EEG – FHR monitoring allows for early detection of worsening hypoxic-acidemia similar to that shown for ECOG-FHR monitoring. Near-term fetal sheep (n = 9) were chronically instrumented with arterial and venous catheters, ECG, ECOG, and EEG electrodes and umbilical cord occluder, followed by 4 days of recovery. Repetitive UCOs of 1 min duration and increasing strength (with regard to the degree of reduction in umbilical blood flow) were induced each 2.5 min until pH dropped to <7.00. Repetitive UCOs led to marked acidosis (arterial pH 7.35 ± 0.01 to 7.00 ± 0.03). At pH of 7.22 ± 0.03 (range 7.32–7.07), and 45 ± 9 min (range 1 h 33 min–20 min) prior to attaining pH < 7.00, both ECOG and EEG amplitudes began to decrease ∼fourfold during each FHR deceleration in a synchronized manner. Confirming our hypothesis, these findings support fetal EEG as a useful adjunct to FHR monitoring during human labor for early detection of incipient fetal acidemia.

Noninvasive Recording of True-to-Form Fetal ECG during the Third Trimester of Pregnancy

Objective. The aim of the study was to develop a complex electrophysiological measurement system (hardware and software) which uses the methods of electrophysiology and provides significant information about the intrauterine status of the fetus, intending to obtain true-to-form, morphologically evaluated fetal ECG from transabdominal maternal lead. Results. The present method contains many novel ideas that allow creating true-to-form noninvasive fetal ECG in the third trimester of the pregnancy in 80% of the cases. Such ideas are the telemetric data collection, the “cleanse” of the real time recording from the maternal ECG, and the use of the cardiotocograph (CTG) that allows identifying the fetal heart events. The advantage of this developed system is that it does not require any qualified staff, because both the extraction of the information from the abdominal recording and the processing of the data are automatic. Discussion. Although the idea of a noninvasive fetal electrocardiography is more than 100 years old still there is no simple, effective, and cheap method available that would enable an extensive use. This developed system can be used in the third trimester of the pregnancy efficiently. It can produce true-to-form fetal ECGs with amplitude less than 10 µV.

Power spectral analysis of two-channel EEG in very premature infants undergoing heat loss prevention

OBJECTIVE

To evaluate whether wearing a wool cap, a routine practice used to prevent heat loss in premature infants, affects interpretation of electroencephalogram spectral analysis.

METHODS

Eighteen premature infants (median gestational age 28 weeks, range 23-32) without neurological complications were randomized to two channel (C3, C4 referred to Cz) digital electroencephalogram recordings with (90 min) and without (90 min) wearing wool cap, at 4 days of life. Electroencephalogram was analyzed automatically by measurement of burst suppression ratio and asymmetry index and by Fast Fourier Transform to calculate total absolute spectral power; relative spectral power in the δ (0.5-3.5 Hz), θ (4-7.5 Hz), α (8-12.5 Hz), and β (13-30 Hz) frequency bands; spectral edge frequency; and mean dominant frequency.

RESULTS

The use of wool cap had no effect on all electroencephalogram parameters considered. Gestational age showed an effect on relative spectral power of all considered bands, spectral edge frequency and mean dominant frequency, while no effect was seen on burst suppression ratio and asymmetry index. Neonates born at gestational weeks lower than 28 had significantly higher relative power in the δ band and lower relative power in the α and β bands.

CONCLUSIONS

Heat loss prevention using wool cap does not affect interpretation of spectral electroencephalogram. Spectral values in our group of very premature infants without neurological complications correspond to normal data reported in the literature. Maturation changes consist of reduction of relative power of the δ band, spectral edge frequency and mean dominant frequency.

Neonatal encephalopathy: an inadequate term for hypoxic-ischemic encephalopathy

This Point of View article addresses neonatal encephalopathy (NE) presumably caused by hypoxia-ischemia and the terminology currently in wide use for this disorder. The nonspecific term NE is commonly utilized for those infants with the clinical and imaging characteristics of neonatal hypoxic-ischemic encephalopathy (HIE). Multiple magnetic resonance imaging studies of term infants with the clinical setting of presumed hypoxia-ischemia near the time of delivery have delineated a topography of lesions highly correlated with that defined by human neuropathology and by animal models, including primate models, of hypoxia-ischemia. These imaging findings, coupled with clinical features consistent with perinatal hypoxic-ischemic insult(s), warrant the specific designation of neonatal HIE.

Monitoring fetal electrocortical activity during labour for predicting worsening acidemia: a prospective study in the ovine fetus near term

Background

Severe fetal acidemia during labour with arterial pH below 7.00 is associated with increased risk of hypoxic-ischemic brain injury. Electronic fetal heart rate (FHR) monitoring, the mainstay of intrapartum surveillance, has poor specificity for detecting fetal acidemia. We studied brain electrical activity measured with electrocorticogram (ECOG) in the near term ovine fetus subjected to repetitive umbilical cord occlusions (UCO) inducing FHR decelerations, as might be seen in human labour, to delineate the time-course for ECOG changes with worsening acidemia and thereby assess the potential clinical utility of fetal ECOG.

Methodology/Principal Findings

Ten chronically catheterized fetal sheep were studied through a series of mild, moderate and severe UCO until the arterial pH was below 7.00. At a pH of 7.24±0.04, 52±13 min prior to the pH dropping <7.00, spectral edge frequency (SEF) increased to 23±2 Hz from 3±1 Hz during each FHR deceleration (p<0.001) and was correlated to decreases in FHR and in fetal arterial blood pressure during each FHR deceleration (p<0.001).

Conclusions/Significance

The UCO-related changes in ECOG occurred in advance of the pH decreasing below 7.00. These ECOG changes may be a protective mechanism suppressing non-essential energy needs when oxygen supply to the fetal brain is decreased acutely. By detecting such “adaptive brain shutdown,” the need for delivery in high risk pregnant patients may be more accurately predicted than with FHR monitoring alone. Therefore, monitoring fetal electroencephalogram (EEG, the human equivalent of ECOG) during human labour may be a useful adjunct to FHR monitoring.

Fetal cerebral blood flow, electrocorticographic activity, and oxygenation: responses to acute hypoxia

Arterial blood gases are critical in regulation of cerebral blood flow (CBF) and cerebral metabolic rate for O(2) (CMRO(2)). However, the relation of these variables to cortical tissue (t ), and electrocorticographic (ECoG) activity (high voltage low frequency, HVLF, versus low voltage high frequency, LVHF), are not well defined. In the fetus, we tested the hypothesis that ECoG pattern is associated closely with cerebral oxygenation. In fetal sheep (n = 8) with laser Doppler flowmeter, fluorescent O(2) probe and ECoG electrodes, we measured laser Doppler CBF (LD-CBF), tP(O2), ECoG and spectral edge frequency-90 (SEF(90)) in response to 40 min isocapnic hypoxia. In the normoxic fetus, LD-CBF and CMRO(2) correlated highly with ECoG state. With a shift from HVLF to LVHF, tP(O2) decreased followed by increased LD-CBF (18%) and CMRO(2) (13%). With acute hypoxia (P(aO2)= 12 +/- 1 Torr), tp(O2) decreased toapproximately 3 Torr, LD-CBF increased 48 +/- 10%, ECoG shifted to chiefly the HVLF state, SEF(90) decreased approximately 15%, and CMRO(2) decreased approximately 20% (P < 0.05 for each). For the normoxic fetus, CBF was closely related to ECoG state, but this association was less evident during acute hypoxia. We speculate that, in the otherwise stressed fetus, acute hypoxia may further compromise cerebral oxygenation.

THE RELATIONSHIP OF HRV TO SLEEP EEG AND SLEEP RHYTHM

Previous studies have shown that there exists a cycle of NREM (non-rapid eye movement)-REM (rapid eye movement) during normal human sleep, and heart rate variability (HRV) has a close relationship to sleep stages and sleep cycle. This article reports the relationship between the electroencephalographic activity and the HRV spectral power in several specific frequency bands. The authors discovered that relationships do exist between HRV and electroencephalogram (EEG) during sleep. In particular, it was found that, prior to the changes of EEG, the changes of HRV usually indicate the shift of sleep stages. HRV frequency analysis indicates that the very-low-frequency components of HRV are closely related to sleep EEG. Results show that the rhythm of the spectral power oscillations in some specific frequency bands of HRV is almost the same as the sleep cycle, which reflects the rhythm of sleep to a certain extent.

Magnetoencephalography in healthy neonates

OBJECTIVE

To describe magnetoencephalography (MEG) recordings in a cohort of healthy neonates.

METHODS

We performed MEG and single channel EEG concomitantly in 21 healthy newborns. MEG and EEG signals were reviewed for gross comparison of general patterns and individual waveform characteristics. Spectral analysis was performed to quantify the signals.

RESULTS

Our MEG recordings showed patterns comparable to classical neonatal EEG. Seventy-nine percent of the subjects exhibited the 'continuous polyfrequency activity' at some point in their recording. Sixty-three percent had the 'continuous slow' pattern, and 47% had the 'trace alternant' pattern. Spectral analysis revealed maximal power at frequencies of less than 4 Hz (delta band) in both MEG and EEG with a decline towards higher frequencies.

CONCLUSIONS

Neonatal MEG is feasible and shares the basic EEG features and frequency content, with predominant activity in the slow frequency delta band. The latter corresponds to reports from earlier neonatal EEG studies.

SIGNIFICANCE

MEG may prove to be useful in studies of neonatal brain functions.

The importance of ‘awareness’ for understanding fetal pain

Our understanding of when the fetus can experience pain has been largely shaped by neuroanatomy. However, completion of the cortical nociceptive connections just after mid-gestation is only one part of the story. In addition to critically reviewing evidence for whether the fetus is ever awake or aware, and thus able to truly experience pain, we examine the role of endogenous neuro-inhibitors, such as adenosine and pregnanolone, produced within the feto-placental unit that contribute to fetal sleep states, and thus mediate suppression of fetal awareness. The uncritical view that the nature of presumed fetal pain perception can be assessed by reference to the prematurely born infant is challenged. Rigorously controlled studies of invasive procedures and analgesia in the fetus are required to clarify the impact of fetal nociception on postnatal pain sensitivity and neural development, and the potential benefits or harm of using analgesia in this unique setting.

Spectral analyses of electroencephalography and heart rate variability during sleep in normal subjects

We investigated the relationship between electroencephalogram (EEG) activity and autonomic nervous system function using spectral analyses of EEG and heart rate variability (HRV) in healthy subjects during sleep. Eleven subjects were enrolled in this study. From EEG, the spectral edge frequencies (SEFs including SEF50, SEF90 and SEF95) were calculated. From electrocardiogram (ECG), the spectral powers of low-frequency band (LF: 0.04-0.15 Hz), high-frequency band (HF: 0.15-0.4 Hz) and the ratio of LF to HF (LF/HF) were calculated. During sleep, each set of data was obtained as the average of a 5-min measurement. We found that SEFs and LF/HF or LF decreased simultaneously and periodically, suggesting simultaneous depression of EEG activity and relative sympathetic activity, and SEFs significantly correlated with LF/HF and LF in all subjects during sleep, but not with HF. The existence of a clear correlation of SEFs with LF or LF/HF may offer a simple approach to estimate the relationship between EEG activity and autonomic nervous system function during sleep.

Lowered electroencephalographic spectral edge frequency predicts the presence of cerebral white matter injury in premature infants

OBJECTIVE

Current methods for early identification of cerebral white matter injury in the premature infant at the bedside are inadequate. This study investigated the utility of advanced spectral analysis of the neonatal electroencephalogram (EEG) in the early diagnosis of white matter injury in the premature infant. The critical measurement used, suggested largely by previous studies in animal models, was the spectral edge frequency (SEF), calculated here as the frequency below which 90% of the power in the EEG exists.

METHODS

Fifty-nine very low birth weight infants (87% of eligible infants) had electrodes placed over the central and parietal regions (C3, P3, C4, and P4 sites according to the 10-20 international system) for the collection of EEG amplitude, intensity, and SEF. All averaged signals were analyzed off-line using software (Chart Analyzer; BrainZ Instruments, Auckland, NZ). All infants had a magnetic resonance imaging scan at term to identify the presence and severity of white matter injury.

RESULTS

There was no significant difference between conventional EEG amplitude and intensity for infants with or without evidence of white matter injury. However, premature infants with increasingly severe white matter injury had progressively lower SEFs compared with infants who did not exhibit white matter injury.

CONCLUSIONS

These data suggest that SEF-based measures are useful for defining the presence and severity of white matter injury at the bedside.