For their new experiments, the Duke team developed a model using pregnant sheep. When the sheep fetus was approximately 17 weeks old an age that approximates a third-trimester human pregnancy the researchers exposed the mother to a three-drug anesthetic combination commonly used to produce general anesthesia. The exposures lasted four hours, a length of time that would encompass most surgeries conducted on pregnant patients.
"We found that four hours of maternal general anesthesia produced an initial increase in systematic oxygenation in the fetus, as well as a sustained increase in oxygenation in the brain," Reynolds said.
The researchers could document cerebral oxygenation in real time because of a system they optimized for fetal applications. The technique, called near-infrared spectroscopy, was originally conceived in the 1970s by Duke faculty member Franz Jobsis.
Light in the near-infrared range can easily pass through skin, bone and other tissues. However, within these frequencies of light, the oxygen-carrying molecules within red blood cells known as hemoglobin absorb light to an extent based on their oxygen content -- giving the researchers a reliable indicator of cerebral oxygenation. Researchers place a fiberoptic probe against the skull of the fetus to measure the changing oxygenation levels of blood circulating in the brain, Reynolds said.
Reynolds said that the increase in oxygenation in the fetal brain is likely due to isoflurane, one of the three commonly used agents, which induced reductions in oxygen metabolism along with increases in cerebral blood flow. Isoflurane is known to produce these actions in the adult brain but it had not been appreciated that such effects could also occur in the fetal brain, he s
Contact: Richard Merritt
Duke University Medical Center