Effect of repetitive umbilical cord occlusions on neuronal brain activity measured by the cerebral function analyzing monitor and histologic outcome in immature fetal sheep.

OBJECTIVE: To examine the effect of repetitive total umbilical cord occlusions on electrocortical brain activity as measured by cerebral function analyzing monitoring (CAFM) and the histologic outcome in immature sheep fetuses.

STUDY DESIGN: We performed brief repeated total umbilical cord occlusions, two every 5 minutes, in 12 immature sheep fetuses (at 90 days of gestation, term 147 days) until fetal mean arterial pressure dropped below 50% of baseline value during two successive occlusions. A pair of electrodes was inserted on the parietal dura for recording of electrocortical brain activity (ECoG). Off-line ECoG signal processing consisted of amplitude integrated analysis (CFAM) and spectral analysis. Fetal blood gas analyses were performed at regular intervals just before subsequent umbilical cord occlusions. Three days after the occlusion neuronal damage was evaluated histologically in three regions of the fetal brain.

RESULTS: CFAM amplitide parameters decreased significantly during the first occlusion and remained so during the entire repetitive occlusion period (analysis of variance [ANOVA]; P <.05). Spectral analysis of the ECoG signal demonstrated no changes in the distribution of frequency bands. Progressive acidemia and hypotension developed with ongoing occlusions. Five fetuses died at the end or shortly after the entire repetitive occlusion period. No neuronal damage or macroscopic intraventricular and/or germinal matrix hemorrhage was observed in the surviving fetuses.

CONCLUSION: Repetitive umbilical cord occlusions in immature sheep fetuses resulted in functional, not structural changes of the fetal brain in surviving fetuses. At this gestational age, amplitude analysis is more sensitive than spectral analysis of the ECoG signal to functional changes of the compromised fetal brain.