Monitoring Fetal Electrocortical Activity during Labour for Predicting Worsening Acidemia: A Prospective Study in the Ovine Fetus Near Term

Department of Obstetrics and Gynecology, Lawson Health Research Institute, The University of Western Ontario, London, Ontario, Canada.
PLoS ONE (Impact Factor: 3.23). 07/2011; 6(7):e22100. DOI: 10.1371/journal.pone.0022100
Source: PubMed


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.
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).
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.

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    • "Thus, for earlier detection of fetal acidemia during labor as herein shown with RMSSD as a measure of fHRV, more sensitive means of acquiring FHR are recommended than currently deployed in EFM. Candidates for alternative means of fetal assessment for detecting the onset of hypoxic-acidemia include trans-abdominal ECG, already used at the bedside in some jurisdictions, or experimental approaches involving fetal EEG during labor (22–24). Fetal scalp ECG could also be sampled at 1000 Hz, thus permitting true fHRV analyses such as presented here. "
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    ABSTRACT: Background: To evaluate the impact of sampling rate on the predictive capability of continuous fetal heart rate (FHR) variability (fHRV) monitoring for detecting fetal acidemia during labor, we tested the performance of the root mean square of successive differences (RMSSD) in R–R intervals from the ECG when acquired with the sampling rate of 4 Hz currently available in FHR monitors, in comparison to the gold standard of 1000 Hz. Methods: Near-term ovine fetuses (N = 9) were chronically prepared with precordial electrodes for recording ECG, vascular catheters for blood sampling, and an umbilical cord occluder. For 1 min every 2.5 min, animals underwent mild partial umbilical cord occlusions (UCO) × 1 h, moderate partial UCO × 1 h, then complete UCO × 2 h, or until arterial pH reached <7.00. Arterial blood samples were drawn at baseline and every 20 min during the UCO series. RMSSD was calculated continuously in 5 min windows using an automated, standardized system ( Results are presented as mean ± SEM with significance assumed for p < 0.05. Results: Repetitive UCO resulted in pH decreasing from 7.35 ± 0.01 to 7.00 ± 0.03. In all nine animals, RMSSD increased from 16.7 ± 1.0 ms at baseline to 44.4 ± 2.3 ms, 70 ± 15 min prior to reaching the pH nadir when sampled at 1000 Hz. When sampled at 4 Hz, RMSSD at baseline measured 36.1 ± 6.0 ms and showed no significant increase during the UCO series until the pH nadir was reached. Consequently, early detection of severe hypoxic-acidemia would have been missed in all fetuses. Conclusion: RMSSD as a measure of fHRV when calculated from FHR sampled at 1000 Hz allowed for the early detection of worsening hypoxic-acidemia in each fetus. However, when calculated at the low sampling rate of 4 Hz used clinically, RMSSD remained unchanged until terminally when the nadir pH was reached. For early detection of fetal acidemia during labor, more sensitive means of acquiring FHR are therefore recommended than currently deployed, e.g., trans-abdominal fetal ECG.
    Frontiers in Pediatrics 05/2014; 2:38. DOI:10.3389/fped.2014.00038
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    • "This neuroprotective response has also been described during repeated umbilical cord occlusions in healthy near-term fetal sheep, with rapid and reversible suppression of EEG activity approximately 90 seconds after the onset of each occlusion, with superior sagittal sinus blood flow and arterial blood pressure values that were maintained at or above baseline values [10,11]. In contrast, Frash et al. observed EEG suppression only when one-minute occlusions were repeated every 2 minutes, and coincided with worsening acidemia and hypotension [12]. In addition, De Haan et al. reported that suppression of EEG activity was both faster and more profound during 2-minute occlusions repeated every 5 minutes compared to 1-minute occlusions repeated every 2.5 minutes, and associated with greater frequency of epileptiform and spike activity between occlusions [13]. "
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    ABSTRACT: Spontaneous antenatal hypoxia is associated with high risk of adverse outcomes, however, there is little information on neural adaptation to labor-like insults. Chronically instrumented near-term sheep fetuses (125 ± 3 days, mean ± SEM) with baseline PaO2 < 17 mmHg (hypoxic group: n = 8) or > 17 mmHg (normoxic group: n = 8) received 1-minute umbilical cord occlusions repeated every 5 minutes for a total of 4 hours, or until mean arterial blood pressure (MAP) fell below 20 mmHg for two successive occlusions. 5/8 fetuses with pre-existing hypoxia were unable to complete the full series of occlusions (vs. 0/8 normoxic fetuses). Pre-existing hypoxia was associated with progressive metabolic acidosis (nadir: pH 7.08 ± 0.04 vs. 7.33 ± 0.02, p<0.01), hypotension during occlusions (nadir: 24.7 ± 1.8 vs. 51.4 ± 3.2 mmHg, p<0.01), lower carotid blood flow during occlusions (23.6 ± 6.1 vs. 63.0 ± 4.8 mL/min, p<0.01), greater suppression of EEG activity during, between, and after occlusions (p<0.01) and slower resolution of cortical impedance, an index of cytotoxic edema. No normoxic fetuses, but 4/8 hypoxic fetuses developed seizures 148 ± 45 minutes after the start of occlusions, with a seizure burden of 26 ± 6 sec during the inter-occlusion period, and 15.1 ± 3.4 min/h in the first 6 hours of recovery. In conclusion, in fetuses with pre-existing hypoxia, repeated brief asphyxia at a rate consistent with early labor is associated with hypotension, cephalic hypoperfusion, greater EEG suppression, inter-occlusion seizures, and more sustained cytotoxic edema, consistent with early onset of neural injury.
    PLoS ONE 08/2013; 8(8):e73895. DOI:10.1371/journal.pone.0073895 · 3.23 Impact Factor
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    • "Short periods of fetal electrocortical suppression have been reported during labor in humans without any consequences [15]. An adaptive mechanism has been implicated in such short suppression of synaptic transmission activity, where a state of decrease energy requirement is developed to withstand longer hypoxic insults induced by episodes of complete cord occlusion (to mimic uterine contraction in labour) in animal models [16]. In an ovine fetal brain, this adaptive metabolic shutdown appears to be mediated also by endogenous activation of adenosine A1 receptors during critical decreases in oxygenation [17, 18]. "
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    ABSTRACT: We describe the EEG findings from an ex-preterm neonate at term equivalent age who presented with intermittent but prolonged apneic episodes which were presumed to be seizures. A total of 8 apneic episodes were captured (duration 23-376 seconds) during EEG monitoring. The baseline EEG activity was appropriate for corrected gestational age and no electrographic seizure activity was recorded. The average baseline heart rate was 168 beats per minute (bpm) and the baseline oxygen saturation level was in the mid-nineties. Periods of complete EEG suppression lasting 68 and 179 seconds, respectively, were recorded during 2 of these 8 apneic episodes. Both episodes were accompanied by bradycardia less than 70 bpm and oxygen saturation levels of less than 20%. Short but severe episodes of apnea can cause complete EEG suppression in the neonate.
    03/2012; 2012(6):250801. DOI:10.1155/2012/250801
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