新生猪缺氧缺血性脑损伤模型中脑氧饱和度－时间阈值的研究

背景危重新生儿缺氧缺血性脑病（hypoxia．ischemia，H．I）的检测和脑损伤预防是目前的难题。近红外光谱分析（near—infraredspecVoscopy，NIRS）作为一种无创的床边监测技术可以解决上述问题，但是，对于脑损伤中NIRS脑氧饱和度（O，saturation，ScO2）的存活力-时间阈值，目前尚不明确。本研究目的是探讨ScO2为35％时的H—I持续时间（引起神经生理障碍的存活力闽值）与神经系统预后的关系。方法46头新生猪，经芬太尼．咪达唑仑麻醉后，放置NIRS及脑功能监测（cerebralfunc．tionmonitor，CFM）探头，记录ScO2及脑皮质电活动（eleclrocorticalactivity，ECA）。夹闭颈总动脉后，调节吸入氧浓度复制出H—I模型（ScO2为35％同时伴有ECA降低）。分别于H-I1小时、2小时、3小时、4小时、6小时及8小时后，通过神经行为学及组织病理学评价存活个体的神经系统预后情况。结果H—I持续1小时或2小时，ECA及ScO2在再灌注期很快恢复正常，受试个体的神经功能也恢复至正常水平。H-I持续时间超过2-3小时，再灌注期ECA显著下降，ScO2则明显增加，提示体内存在组织氧代谢持续受抑制。H—I持续时间超过2小时，神经损伤的发生率呈线性增加，约为每小时增加15％。结论ScO2达35％时，H-I损伤的生存一时间阈值为2—3小时，标志为再灌注期NIRS及CFM出现异常。本研究结果提示，联合应用NIRS和CFM有助于预测神经系统的预后，H—I损伤期间存在几个小时的时间窗，可以有效的预防神经功能损伤。

BACKGROUND： Detection of cerebral hypoxia-ischemia （H-I） and prevention of brain injury remains problematic in critically ill neonates. Near-infrared spectroscopy （NIRS）, a noninvasive bedside technology could fill this role, although NIRS cerebral 02 saturation （SCO2） viabifity-time thresholds for brain injury have not been determined. We investigated the relationship between H-I duration at ScO2 35%, a viability threshold which causes neurophysiological impairment, to neurological outcome. METHODS： Forty-six fentanyl-midazolam anesthetized piglets were equipped with NIRS and cerebral function monitor （CFM） to record ScO2 and electrocortical activity （ECA）. After carotid occlusion, inspired O2 was adjusted to produce H-I （ScO2 35% with decreased ECA） for 1,2,3,4, 6 or 8 h in different groups, followed by survival to assess neurological outcome by behavioral and histological examination. RESULTS： For H-I lasting 1 or 2 h, ECA and ScO2 during reperfusion rapidly returned to normal and neurological outcomes were normal. For H-I more than 2 - 3 h, ECA was significantly decreased and ScO2 was significantly increased during reperfusion, suggesting continued depression of tissue O2 metabolism. As H-I increased beyond 2 h, the incidence of neurological injury increased linearly, approximately 15% per h. CONCLUSIONS： Aviability-time threshold for H-I injury is ScO2 of 35% for 2 -3 h, heralded by abnormalities in NIRS and CFM during reperfusion. These findings suggest that NIRS and CFM might be used together to predict neurological outcome. and illustrate that there is a several hour window of opportunity during H-I to prevent neurological injury.