Positive end expiratory pressure (PEEP) improves oxygenation in mechanically ventilated preterm neonates by preventing lung collapse. However, high PEEP may alter cerebral blood flow secondary to the increased intrathoracic pressure, predisposing to brain injury. The precise effects of high PEEP on cerebral haemodynamics in the preterm brain is unknown. We aimed to assess the effect of PEEP on microvessels in the preterm brain using synchrotron radiation (SR) microangiography which, enables in vivo real-time high-resolution imaging of the cerebral vasculature. Preterm lambs (0.8 gestation, n=4) were delivered via caesarean section, anaesthetised and ventilated. SR microangiography of the right cerebral hemisphere was performed with iodine contrast administered into the right carotid artery, during PEEP ventilation of 5 and 10 cmH₂O respectively. Carotid blood flow was measured using an ultrasonic flow probe placed around the left carotid artery. An increase of PEEP from 5 to 10 cmH₂O increased the diameter of small cerebral vessels (<150 µm), but decreased diameter of larger cerebral vessels (>500 µm) in all 4 lambs. Additionally, the higher PEEP increased the cerebral contrast transit time in 3 of the 4 lambs. Carotid blood flow increased in 2 lambs which, also had increased carbon dioxide levels during PEEP 10. Our results suggest that PEEP of 10 cmH₂O alters the preterm cerebral haemodynamics, with prolonged cerebral blood flow transit and engorgement of small cerebral microvessels likely due to the increased intrathoracic pressure. These microvascular changes are generally not reflected in global assessment of cerebral blood flow or oxygenation.

中文翻译：

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通气早产羔羊的呼气末峰值压力增加改变了脑微血管灌注：直接同步加速器微血管造影评估。

呼气末正压（PEEP）通过防止肺衰竭来改善机械通气早产儿的氧合作用。但是，高PEEP可能会继发于胸腔内压力增加而改变脑血流量，从而容易导致脑损伤。高PEEP对早产儿大脑血流动力学的确切影响尚不清楚。我们旨在使用同步加速器辐射（SR）微血管造影术评估PEEP对早产儿大脑微血管的作用，该技术可在体内对大脑脉管系统进行实时高分辨率成像。早产羔羊（0.8胎，n = 4）经剖腹产后麻醉并通气。在PEEP通气5和10 cmH期间，对右颈动脉进行碘造影，对右半脑进行SR微血管造影₂ Ó分别。使用放置在左颈动脉周围的超声流量探头测量颈动脉血流量。PEEP从5 cmH ₂ O增加到10 cmH ₂ O增加了所有4只羔羊的小脑血管的直径（<150 µm），但减小了大脑血管的直径（> 500 µm）。此外，较高的PEEP会增加4只羔羊中3只的大脑造影剂传输时间。2只羔羊的颈动脉血流量增加，PEEP 10期间的二氧化碳含量也增加。我们的结果表明，PEEP为10 cmH ₂O改变早产儿的脑血流动力学，延长的脑血流传输和充血的小脑微血管充血可能是由于胸腔内压力升高所致。这些微血管变化通常不会反映在脑血流量或氧合的总体评估中。