Surveillance non invasive de la réponse neuroimmunitaire fœtale à l’infection

Introduction. In utero, l’infection des membranes maternelles et fœtales, la chorioamniotite, passe souvent inaperçue et, en particulier lorsque associée à une acidémie, due à l’occlusion du cordon ombilical (OCO), comme il se produirait au cours du travail, peut entrainer des lésions cérébrales et avoir des répercussions neurologiques péri - et postnatales à long terme chez le fœtus. Il n'existe actuellement aucun moyen de détecter précocement ces conditions pathologiques in utéro afin de prévenir ou de limiter ces atteintes. Hypothèses. 1)l’électroencéphalogramme (EEG) fœtal obtenu du scalp fœtal pourrait servir d’outil auxiliaire à la surveillance électronique fœtale du rythme cardiaque fœtal (RCF) pour la détection précoce d'acidémie fœtale et d'agression neurologique; 2) la fréquence d’échantillonnage de l’ECG fœtal (ECGf) a un impact important sur le monitoring continu de la Variabilité du Rythme Cardiaque (VRCf) dans la prédiction de l’acidémie fœtale ; 3) les patrons de la corrélation de la VRCf aux cytokines pro-inflammatoires refléteront les états de réponses spontanées versus inflammatoires de la Voie Cholinergique Anti-inflammatoire (VCA); 4) grâce au développement d’un modèle de prédictions mathématiques, la prédiction du pH et de l’excès de base (EB) à la naissance sera possible avec seulement une heure de monitoring d’ECGf. Méthodes. Dans une série d’études fondamentales et cliniques, en utilisant respectivement le mouton et une cohorte de femmes en travail comme modèle expérimental et clinique , nous avons modélisé 1) une situation d’hypoxie cérébrale résultant de séquences d’occlusion du cordon ombilical de sévérité croissante jusqu’à atteindre un pH critique limite de 7.00 comme méthode expérimentale analogue au travail humain pour tester les première et deuxième hypothèses 2) un inflammation fœtale modérée en administrant le LPS à une autre cohorte animale pour vérifier la troisième hypothèse et 3) un modèle mathématique de prédictions à partir de paramètres et mesures validés cliniquement qui permettraient de déterminer les facteurs de prédiction d’une détresse fœtale pour tester la dernière hypothèse. Résultats. Les séries d’OCO répétitives se sont soldés par une acidose marquée (pH artériel 7.35±0.01 à 7.00±0.01), une diminution des amplitudes à l'électroencéphalogramme( EEG) synchronisé avec les décélérations du RCF induites par les OCO accompagnées d'une baisse pathologique de la pression artérielle (PA) et une augmentation marquée de VRCf avec hypoxie-acidémie aggravante à 1000 Hz, mais pas à 4 Hz, fréquence d’échantillonnage utilisée en clinique. L’administration du LPS entraîne une inflammation systémique chez le fœtus avec les IL-6 atteignant un pic 3 h après et des modifications de la VRCf retraçant précisément ce profil temporel des cytokines. En clinique, avec nos cohortes originale et de validation, un modèle statistique basée sur une matrice de 103 mesures de VRCf (R2 = 0,90, P < 0,001) permettent de prédire le pH mais pas l’EB, avec une heure d’enregistrement du RCF avant la poussée. Conclusions. La diminution de l'amplitude à l'EEG suggère un mécanisme d'arrêt adaptatif neuroprotecteur du cerveau et suggère que l'EEG fœtal puisse être un complément utile à la surveillance du RCF pendant le travail à haut risque chez la femme. La VRCf étant capable de détecter une hypoxie-acidémie aggravante tôt chez le fœtus à 1000Hz vs 4 Hz évoque qu’un mode d'acquisition d’ECG fœtal plus sensible pourrait constituer une solution. Des profils distinctifs de mesures de la VRCf, identifiés en corrélation avec les niveaux de l'inflammation, ouvre une nouvelle voie pour caractériser le profil inflammatoire de la réponse fœtale à l’infection. En clinique, un monitoring de chevet de prédiction du pH et EB à la naissance, à partir de mesures de VRCf permettrait des interprétations visuelles plus explicites pour des prises de décision plus exactes en obstétrique au cours du travail.Introduction. In utero, the infection of maternal and fetal membranes, chorioamnionitis, goes frequently unnoticed and, especially when combined with acidemia due to occlusions of the umbilical cord as they occur during labour, can result in brain damage and long term neurological sequelae peri- and postnatally. Currently, there is no way to early detect these pathological conditions to prevent or limit lasting neurological deficits. Hypotheses. (1) the fetal electroencephalogram (EEG), obtained from the scalp could serve as a useful ancillary tool to the existing fetal heart rate (FHR) monitoring for early detection of fetal acidemia and neurological injury; (2) the sampling rate of fetal ECG has a significant impact on the continuous FHR monitoring in the prediction of fetal acidemia; 3) patterns of FHR variability will reflect fetal baseline and inflammatory states; (4) FHR variability analysis should permit prediction of pH and base excess (BE) at birth. Methods. In a series of studies using the chronically instrumented unanesthetized fetal sheep and clinical cohort, we modeled 1) worsening fetal acidemia with intermittent hypoxia resulting from umbilical cord occlusions (UCO) of increasing severity as experimental model of human labour to test the 1st and 2nd hypotheses; 2) moderate fetal inflammation by administering lipopolysaccharide (LPS) to test the 3rd hypothesis and 3) prediction of pH and BE status at birth using clinically validated FHR variability measures in a clinical cohort of laboring women to test the 4th hypothesis. Results. Repetitive UCO resulted in marked acidosis (pH arterial 7.35±0.01 to 7.00±0.01), decreased EEG amplitudes synchronized with UCO-induced FHR decelerations and pathological arterial blood pressure decreases; in addition, we detected a significant increase in FHR variability with worsening acidemia when sampled at 1000 but not at 4 Hz, the sampling rate used clinically. LPS administration resulted in systemic fetal inflammation with IL-6 peaking at 3 h and FHR variability changes tracking this temporal cytokine profile precisely. In the clinical cohort, a statistical model based on a matrix of 103 FHR variability measures predicted pH (R2 = 0.90, P < 0.001), but not BE, from one hour of FHR recording prior to pushing stage. Conclusions. The decrease in the EEG amplitude suggests an adaptive and neuroprotective brain shut-down; fetal EEG may complement the FHR monitoring during labour to improve early detection of incipient acidemia. FHR variability changes can detect early developing hypoxic-acidemia when sampled at 1000 Hz, but not when sampled at 4 Hz suggesting that a more sensitive mode of fetal ECG acquisition will improve early acidemia detection. Distinctive subsets of FHR variability measures permit online monitoring of fetal inflammation from ECG opening a new approach to characterizing the fetal inflammatory profile. Clinical bedside prediction of pH and BE monitoring at birth using FHR variability monitoring will allow more accurate decision making in obstetrics during labou

Adaptive Brain Shut-Down Counteracts Neuroinflammation in the Near-Term Ovine Fetus

Objective: Repetitive umbilical cord occlusions (UCOs) in ovine fetus leading to severe acidemia result in adaptive shut-down of electrocortical activity (ECOG) as well as systemic and brain inflammation. We hypothesized that the fetuses with earlier ECOG shut-down as a neuroprotective mechanism in response to repetitive UCOs will show less brain inflammation and, moreover, that chronic hypoxia will impact this relationship.Methods: Near term fetal sheep were chronically instrumented with ECOG leads, vascular catheters and a cord occluder and then underwent repetitive UCOs for up to 4 hours or until fetal arterial pH was < 7.00. Eight animals, hypoxic prior to the UCOs (SaO2< 55%), were allowed to recover 24 hours post insult, while 14 animals, five of whom also were chronically hypoxic, were allowed to recover 48 hours post insult, after which brains were perfusion-fixed. Time of ECOG shut-down and corresponding pH were noted, as well as time to then reach pH<7.00 (ΔT). Microglia (MG) were counted as a measure of inflammation in grey matter layers 4-6 (GM4-6) where most ECOG activity is generated. Results are reported as mean±SEM for p<0.05.Results: Repetitive UCOs resulted in worsening acidosis over 3 to 4 hours with arterial pH decreasing to 6.97±0.02 all UCO groups’ animals, recovering to baseline by 24 hours. ECOG shut-down occurred 52±7 min before reaching pH < 7.00 at pH 7.23±0.02 across the animal groups. MG counts were inversely correlated to ΔT in 24 hours recovery animals (R=-0.84), as expected. This was not the case in normoxic 48 hours recovery animals, and, surprisingly, in hypoxic 48 hours recovery animals this relationship was reversed (R=0.90).Conclusion: Adaptive brain shut-down during labour-like worsening acidemia counteracts neuroinflammation in a hypoxia- and time-dependent manner

Sampling rate of heart rate variability impacts the ability to detect acidemia in ovine fetuses near-term

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 labour, 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) x1 h, moderate partial UCO x 1h, then complete UCO x 2 h, or until arterial pH reached Results: Repetitive UCO resulted in pH decreasing from 7.35±0.01 to 7.00±0.03. In all 9 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. Conclusions: 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 labour, more sensitive means of acquiring FHR are therefore recommended than currently deployed