Associations between fetal heart rate variability and umbilical cord occlusions-induced neural injury: An experimental study in a fetal sheep model

INTRODUCTION

This study evaluated the association between fetal heart rate variability (HRV) and the occurrence of hypoxic-ischemic encephalopathy in a fetal sheep model.

MATERIAL AND METHODS

The experimental protocol created a hypoxic condition with repeated cord occlusions in three phases (A, B, C) to achieve acidosis to pH <7.00. Hemodynamic, gasometric and HRV parameters were analyzed during the protocol, and the fetal brain, brainstem and spinal cord were assessed histopathologically 48 h later. Associations between the various parameters and neural injury were compared between phases A, B and C using Spearman's rho test.

RESULTS

Acute anoxic-ischemic brain lesions in all regions was present in 7/9 fetuses, and specific neural injury was observed in 3/9 fetuses. The number of brainstem lesions correlated significantly and inversely with the HRV fetal stress index (r = -0.784; p = 0.021) in phase C and with HRV long-term variability (r = -0.677; p = 0.045) and short-term variability (r = -0.837; p = 0.005) in phase B. The number of neurological lesions did not correlate significantly with other markers of HRV.

CONCLUSIONS

Neural injury caused by severe hypoxia was associated with HRV changes; in particular, brainstem damage was associated with changes in fetal-specific HRV markers.

Physiological control of fetal heart rate variability during labour: Implications and controversies

The interpretation of fetal heart rate (FHR) patterns is the only available method to continuously monitor fetal wellbeing during labour. One of the most important yet contentious aspects of the FHR pattern is changes in FHR variability (FHRV). Some clinical studies suggest that loss of FHRV during labour is a sign of fetal compromise so this is reflected in practice guidelines. Surprisingly, there is little systematic evidence to support this observation. In this review we methodically dissect the potential pathways controlling FHRV during labour-like hypoxaemia. Before labour, FHRV is controlled by the combined activity of the parasympathetic and sympathetic nervous systems, in part regulated by a complex interplay between fetal sleep state and behaviour. By contrast, preclinical studies using multiple autonomic blockades have now shown that sympathetic neural control of FHRV was potently suppressed between periods of labour-like hypoxaemia, and thus, that the parasympathetic system is the sole neural regulator of FHRV once FHR decelerations are present during labour. We further discuss the pattern of changes in FHRV during progressive fetal compromise and highlight potential biochemical, behavioural and clinical factors that may regulate parasympathetic-mediated FHRV during labour. Further studies are needed to investigate the regulators of parasympathetic activity to better understand the dynamic changes in FHRV and their true utility during labour. This article is protected by copyright. All rights reserved.

Changes in S100B and troponin levels in a fetal sheep model of worsening acidosis

BACKGROUND

S100B and cardiac troponin T (c-TnT) are relevant biomarkers at birth of hypoxic-ischemic encephalopathy (HIE) and myocardial ischemia secondary to metabolic acidosis during labor, respectively. The purpose was to assess in-utero changes in S100B and c-TnT levels in an experimental model of labor-like acidosis.

METHODS

Repeated umbilical cord occlusions (UCOs) in ten experiments were performed in mild (phase A, 1 UCO/5 mn), moderate (phase B, 1 UCO/3 mn), and severe (phase C, 1 UCO/2 mn) period. The experiments were stopped if arterial pH reached 6.90.

RESULTS

UCOs resulted in fetal acidosis with pH dropping to 6.99 ±0.13. When compared to the baseline period fetal S100B increased between phases A and B (7% ± 4 vs 17% ± 13, p = 0.030) and between phases A and C (7% ± 4 vs 24% ± 8, p < 0.001). Fetal c-TnT serum levels increased during occlusions: 102 ng/L (58-119) in phase A, vs 119 ng/L (103-198) in phase B vs 169 ng / L (128-268) in phase C (p < 0.05, for all). When compared to the baseline control period, fetal ΔcTnT was significantly modified throughout UCO series: 5.0% (-3; 45) in phase A, 51% (4; 263) in phase B, and 77% (56.5; 269) in phase C (p < 0.05 for all).

CONCLUSIONS

S100B and c-TnT increased when fetal acidosis occurred, which reflects the potential neurological damage and fetal cardiovascular adaptation.

Deceleration area and capacity during labour-like umbilical cord occlusions identify evolving hypotension: a controlled study in fetal sheep

OBJECTIVE

Cardiotocography is widely used to assess fetal well-being during labour. The positive predictive value of current clinical algorithms to identify hypoxia-ischaemia is poor. In experimental studies, fetal hypotension is the strongest predictor of hypoxic-ischaemic injury. Cohort studies suggest that deceleration area and deceleration capacity of the fetal heart rate trace correlate with fetal acidaemia, but it is not known whether they are indices of fetal arterial hypotension.

DESIGN

Prospective, controlled study.

SETTING

Laboratory.

SAMPLE

Near-term fetal sheep.

METHODS

One minute of complete umbilical cord occlusions (UCOs) every 5 minutes (1:5 min, n = 6) or every 2.5 minutes (1:2.5 min, n = 12) for 4 hours or until fetal mean arterial blood pressure fell <20 mmHg.

MAIN OUTCOME MEASURES

Deceleration area and capacity during the UCO series were related to evolving hypotension.

RESULTS

The 1:5 min group developed only mild metabolic acidaemia, without hypotension. By contrast, 10/12 fetuses in the 1:2.5-min group progressively developed severe metabolic acidaemia and hypotension, reaching 16.8 ± 0.9 mmHg after 71.2 ± 6.7 UCOs. Deceleration area and capacity remained unchanged throughout the UCO series in the 1:5-min group, but progressively increased in the 1:2.5-min group. The severity of hypotension was closely correlated with both deceleration area (P < 0.001, R²  = 0.66, n = 18) and capacity (P < 0.001, R²  = 0.67, n = 18). Deceleration area and capacity predicted development of hypotension at a median of 103 and 123 minutes before the final occlusion, respectively.

CONCLUSIONS

Both deceleration area and capacity were strongly associated with developing fetal hypotension, supporting their potential to improve identification of fetuses at risk of hypotension leading to hypoxic-ischaemic injury during labour.

TWEETABLE ABSTRACT

Deceleration area and capacity of fetal heart rate identify developing hypotension during labour-like hypoxia.