Repeated isoflurane exposure and neuroapoptosis in the midgestation fetal sheep brain

Background Advances in surgery and technology have resulted in increased in-utero procedures. However, the effect of anesthesia on the fetal brain is not fully known. The inhalational anesthetic agent, isoflurane, other gamma amino butyric acid agonists (benzodiazepines, barbiturates, propofol, other inhalation anesthetics), and N-methyl D aspartate antagonists, eg, ketamine, have been shown to induce neuroapoptosis. The ovine model has been used extensively to study maternal-fetal physiologic interactions and to investigate different surgical interventions on the fetus. Objective The purpose of this study was to determine effects of different doses and duration of isoflurane on neuroapoptosis in midgestation fetal sheep. We hypothesized that repeated anesthetic exposure and high concentrations of isoflurane would result in increased neuroapoptosis. Study Design Time-dated, pregnant sheep at 70 days gestation (term 145 days) received either isoflurane 2% × 1 hour, 4% × 3 hours, or 2% × 1 hour every other day for 3 exposures (repeated exposure group). Euthanasia occurred following anesthetic exposure and fetal brains were processed. Neuroapoptosis was detected by immunohistochemistry using anticaspase-3 antibodies. Fetuses unexposed to anesthesia served as controls. Another midgestation group with repeated 2% isoflurane exposure was examined at day 130 (long-term group) and neuronal cell density compared to age-matched controls. Representative sections of the brain were analyzed using Aperio Digital imaging (Leica Microsystems Inc, Buffalo Grove, IL). Data, reported by number of neurons per cubic millimeter of brain tissue are presented as means and SEM. Data were analyzed using the Mann-Whitney U and Kruskal-Wallis tests as appropriate. Results A total of 34 fetuses were studied. There was no significant difference in neuroapoptosis observed in fetuses exposed to 2% isoflurane for 1 hour or 4% isoflurane for 3 hours. Increased neuroapoptosis was observed in the frontal cortex following repeated 2% isoflurane exposure compared to controls (1.57 ± 0.22 × 10⁶/mm³ vs 1.01 ± 0.44 × 10⁶/mm³, P =.02). Fetuses at 70 days gestation with repeated exposure demonstrated decreased frontal cortex neurons at day 130 when compared to age-matched controls (2.42 ± 0.3 × 10⁵/mm³ vs 7.32 ± 0.4 × 10⁵/mm³, P =.02). No significant difference in neuroapoptosis was observed between the repeated exposure group and controls in the hippocampus, cerebellum, or basal ganglia. Conclusion Repeated isoflurane exposure in midgestation sheep resulted in increased frontal cortex neuroapoptosis. This persisted into late gestation as decreased neuronal cell density. While animal studies should be extrapolated to human beings with caution, our findings suggest that the number of anesthetic/sedative exposures should be considered when contemplating the risks and benefits of fetal intervention as certain fetal therapies may need to be repeated.