The Ritchie Centre, The Hudson Institute of Medical Research, Melbourne, VIC, Australia.
Department of Paediatrics, Monash University, Melbourne, VIC, Australia.
J Appl Physiol (1985). 2020 Nov 1;129(5):1075-1084. doi: 10.1152/japplphysiol.00652.2020. Epub 2020 Sep 10.
Positive end-expiratory pressure (PEEP) improves oxygenation in mechanically ventilated preterm neonates by preventing lung collapse. However, high PEEP may alter cerebral blood flow secondarily to the increased intrathoracic pressure, predisposing to brain injury. The precise effects of high PEEP on cerebral hemodynamics in the preterm brain are unknown. We aimed to assess the effect of PEEP on microvessels in the preterm brain by using synchrotron radiation (SR) microangiography, which enables in vivo real-time high-resolution imaging of the cerebral vasculature. Preterm lambs (0.8 gestation, = 4) were delivered via caesarean section, anesthetized, 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 cmHO. Carotid blood flow was measured using an ultrasonic flow probe placed around the left carotid artery. An increase of PEEP from 5 to 10 cmHO increased the diameter of small cerebral vessels (<150 µm) but decreased the diameter of larger cerebral vessels (>500 µm) in all four lambs. Additionally, the higher PEEP increased the cerebral contrast transit time in three of the four lambs. Carotid blood flow increased in two lambs, which also had increased carbon dioxide levels during PEEP 10. Our results suggest that PEEP of 10 cmHO alters the preterm cerebral hemodynamics, 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. An increase of positive end-expiratory pressure (PEEP) from 5 to 10 cmHO increased the diameter of small cerebral vessels (<150 µm) but decreased the diameter of larger cerebral vessels (>500 µm). This suggests increased intrathoracic pressure due to high PEEP can drive microvessel engorgement in the preterm brain, which may play a role in cerebrovascular injury.
呼气末正压（PEEP）通过防止肺塌陷来改善机械通气早产儿的氧合。然而，高 PEEP 可能会通过增加胸腔内压力来改变脑血流，从而导致脑损伤。高 PEEP 对早产儿脑的脑血流动力学的确切影响尚不清楚。我们旨在通过使用同步辐射（SR）微血管造影术评估 PEEP 对早产儿脑中小血管的影响，该技术可实现脑血管的体内实时高分辨率成像。通过剖宫产分娩早产儿（0.8 胎龄，n=4），麻醉并进行机械通气。在 5 和 10 cmHO 的 PEEP 通气期间，将碘造影剂注入右侧颈总动脉，进行右侧大脑半球的 SR 微血管造影。通过放置在左侧颈总动脉周围的超声流量探头测量颈动脉血流。从 5 cmHO 增加到 10 cmHO 的 PEEP 增加了所有四只羔羊的小脑血管（<150 µm）的直径，但降低了较大脑血管（>500 µm）的直径。此外，较高的 PEEP 在四只羔羊中的三只增加了脑对比通过时间。在两只羔羊中，PEEP 10 期间二氧化碳水平升高，颈动脉血流增加。我们的结果表明，10 cmHO 的 PEEP 改变了早产儿的脑血流动力学，由于胸腔内压力增加，脑血流通过时间延长，小脑血管充血。这些微血管变化通常不会反映在脑血流或氧合的整体评估中。从 5 cmHO 增加到 10 cmHO 的 PEEP 增加了小脑血管（<150 µm）的直径，但降低了较大脑血管（>500 µm）的直径。这表明高 PEEP 引起的胸腔内压力增加可导致早产儿脑的微血管充血，这可能在脑血管损伤中起作用。
