PurposeInjurious mechanical ventilation causes white matter (WM) injury in preterm infants through inflammatory and haemodynamic pathways. The relative contribution of each of these pathways is not known. We hypothesised that in vivo magnetic resonance imaging (MRI) can detect WM brain injury resulting from mechanical ventilation 24 h after preterm delivery. Further we hypothesised that the combination of inflammatory and haemodynamic pathways, induced by umbilical cord occlusion (UCO) increases brain injury at 24 h.MethodsFetuses at 124±2 days gestation were exposed, instrumented and either ventilated for 15 min using a high tidal-volume (VT) injurious strategy with the umbilical cord intact (INJ; inflammatory pathway only), or occluded (INJ+UCO; inflammatory and haemodynamic pathway). The ventilation groups were compared to lambs that underwent surgery but were not ventilated (Sham), and lambs that did not undergo surgery (unoperated control; Cont). Fetuses were placed back in utero after the 15 min intervention and ewes recovered. Twenty-four hours later, lambs were delivered, placed on a protective ventilation strategy, and underwent MRI of the brain using structural, diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS) techniques.ResultsAbsolute MRS concentrations of creatine and choline were significantly decreased in INJ+UCO compared to Cont lambs (P = 0.03, P = 0.009, respectively); no significant differences were detected between the INJ or Sham groups and the Cont group. Axial diffusivities in the internal capsule and frontal WM were lower in INJ and INJ+UCO compared to Cont lambs (P = 0.05, P = 0.04, respectively). Lambs in the INJ and INJ+UCO groups had lower mean diffusivities in the frontal WM compared to Cont group (P = 0.04). DTI colour mapping revealed lower diffusivity in specific WM regions in the Sham, INJ, and INJ+UCO groups compared to the Cont group, but the differences did not reach significance. INJ+UCO lambs more likely to exhibit lower WM diffusivity than INJ lambs.ConclusionsTwenty-four hours after injurious ventilation, DTI and MRS showed increased brain injury in the injuriously ventilated lambs compared to controls. DTI colour mapping threshold approach provides evidence that the haemodynamic and inflammatory pathways have additive effects on the progression of brain injury compared to the inflammatory pathway alone.

Many preterm neonates require mechanical ventilation which increases the risk of cerebral inflammation and white matter injury in the immature brain. In this review, we discuss the links between ventilation and brain injury with a focus on the immediate period after birth, incorporating respiratory support in the delivery room and subsequent mechanical ventilation in the neonatal intensive care unit. This review collates insight from large animal models in which acute injurious ventilation and prolonged periods of ventilation have been used to create clinically relevant brain injury patterns. These models are valuable resources in investigating the pathophysiology of ventilation-induced brain injury and have important translational implications. We discuss the challenges of reconciling lung and brain maturation in commonly used large animal models. A comprehensive understanding of ventilation-induced brain injury is necessary to guide the way we care for preterm neonates, with the goal to improve their neurodevelopmental outcomes.

Erythropoietin (EPO) is being trialed in preterm neonates for neuroprotection. We have recently demonstrated that a single high bolus dose (5,000 IU/kg) of recombinant human EPO amplified preterm lung and brain ventilation-induced injury. We aimed to determine the optimal dose of EPO to reduce ventilation-induced cerebral white matter inflammation and injury in preterm lambs. Lambs (0.85 gestation) were ventilated with an injurious strategy for 15 min followed by conventional ventilation for 105 min. Lambs were randomized to no treatment (VENT; n = 8) or received a bolus dose of EPO (EPREX®): 300 IU/kg (EPO 300; n = 5), 1,000 IU/kg (EPO 1,000; n = 5), or 3,000 IU/kg (EPO 3,000; n = 5). Physiological parameters were measured throughout the study. After 2 h, brains were collected for analysis; real-time quantitative polymerase chain reaction and immunohistochemistry were used to assess inflammation, cell death, and vascular leakage in the periventricular and subcortical white matter (PVWM; SCWM). Molecular and histological inflammatory indices in the PVWM were not different between groups. EPO 300 lambs had higher IL-6 (p = 0.006) and caspase-3 (p = 0.025) mRNA expression in the SCWM than VENT lambs. Blood-brain barrier (BBB) occludin mRNA levels were higher in EPO 3,000 lambs in the PVWM and SCWM than VENT lambs. The number of blood vessels with protein extravasation in the SCWM was lower in EPO 1,000 (p = 0.010) and EPO 3,000 (p = 0.025) lambs compared to VENT controls but not different between groups in the PVWM. Early administration of EPO at lower doses neither reduced nor exacerbated cerebral white matter inflammation or injury. 3,000 IU/kg EPO may provide neuroprotection by improving BBB integrity.