Cardiovascular responses to mild perinatal asphyxia in growth restricted preterm lambs.

Background: Growth-restricted neonates have worse outcomes after perinatal asphyxia, with more severe metabolic acidosis than appropriately grown neonates. The unique cardiovascular physiology associated with fetal growth restriction (FGR) may hinder growth-restricted neonates' cardiovascular response to asphyxia. However, research on asphyxia in FGR is limited. We aimed to compare cardiovascular haemodynamics in preterm growth-restricted and control lambs during mild perinatal asphyxia. Methods: Single umbilical artery ligation induced FGR in one twin, while the other served as a control. Arterial blood pressure and regional blood flow measurements were taken in preterm lamb fetuses. Mild perinatal asphyxia was induced by umbilical cord clamping, and resuscitation followed neonatal guidelines. Results: MAP changes during asphyxia were similar between groups. Growth-restricted lambs maintained constant carotid blood flow (CBF) for 7 minutes, while control lambs rapidly decreased CBF (P<0.05). Fewer growth-restricted lambs needed chest compressions for return of spontaneous circulation (ROSC) (17 vs 83%, P=0.02). Although the extent of MAP overshoot after ROSC was similar, it took longer for MAP to return to baseline in growth-restricted lambs (18.83±0.00 vs 47.67±0.00 minutes, P=0.003). Growth-restricted lambs had higher CBF after ROSC (P<0.05) and displayed CBF overshoot, unlike control lambs (P<0.03). Conclusions: Preterm growth-restricted lambs may be more resilient to perinatal asphyxia based on prolonged CBF maintenance and reduced need for chest compressions during resuscitation. However, the CBF overshoot after ROSC may increase the risk of cerebrovascular injury in these lambs.