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The premature fetus: not as defenseless as we thought, but still paradoxically vulnerable?
A J Gunn1, J S Quaedackers, J Guan
1Liggins Institute and Department of Pediatrics, University of Auckland, New Zealand. aj.gunn@auckland.ac.nz
Insights
Preterm fetuses show mature cardiovascular and hormonal responses to asphyxia, contrary to previous beliefs. Paradoxically, prolonged survival during asphyxia increases neural injury risk due to hypotension and hypoperfusion.
Area of Science:
- Perinatal physiology
- Neuroprotection
- Fetal development
Background:
- Previous research suggested immature fetal responses to asphyxia, increasing neural injury risk.
- These findings were based on studies using mild insults, not reflecting fetal adaptive capacities.
Purpose of the Study:
- To review the maturation of cardiovascular, cerebrovascular, and cerebral responses to asphyxia in preterm fetuses.
- To evaluate the relationship between these responses and the vulnerability of the premature human brain.
Main Methods:
- Review of experimental animal studies, primarily in chronically instrumented fetal sheep.
- Analysis of cardiovascular, cerebrovascular, and cerebral responses to asphyxia.
Main Results:
- The premature fetus exhibits mature and adaptive responses to asphyxia.
- The preterm brain demonstrates significant resistance to asphyxial injury in absolute terms.
- Prolonged survival during asphyxia is paradoxically linked to hypotension and hypoperfusion.
Conclusions:
- Contrary to traditional views, preterm fetuses possess mature responses to asphyxia.
- While the preterm brain is resistant to injury, prolonged survival strategies paradoxically elevate the risk of severe neural damage due to compromised cerebral perfusion.
Abstract:
Traditionally, it has been believed that the cardiovascular and hormonal responses to asphyxia in preterm fetuses are immature, and this immaturity contributes to their apparent vulnerability to neural injury. However, these data were derived from studies using relatively mild insults, which did not allow for the greater cardiac glycogen reserves and anaerobic capacity of the brain near midgestation. Here, we review the maturation of the cardiovascular and cerebrovascular and cerebral responses to asphyxia in experimental animals and how these relate to the apparent vulnerability of the human premature brain. Most such investigations have been performed in the chronically instrumental fetal sheep. Recent studies have demonstrated that the premature fetus has highly adaptive and relatively mature responses to asphyxia, and that in absolute terms the preterm brain is very resistant to asphyxial injury. These data suggest that the premature fetus is able to survive much more prolonged periods of asphyxia than the near-term fetus, but that, paradoxically, such survival is associated with exposure to prolonged periods of hypotension and hypoperfusion and consequently greater risk of severe neural damage.