Madsen P L, Secher N H
Department of Anaesthesia, the Copenhagen Muscle Research Centre, Rigshospitalet 2041, Denmark.
Prog Neurobiol. 1999 Aug;58(6):541-60. doi: 10.1016/s0301-0082(98)00093-8.
Near-infrared (IR) light easily penetrates biological tissue, and the information offered by in vivo spectroscopy of cerebral oxygenation is detailed and comes with a high temporal resolution. Near-IR light spectroscopy (NIRS) reflects cerebral oxygenation during arterial hypotension, hypoxic hypoxaemia and hypo- and hypercapnia. As determined by dual-wavelength NIRS, the cerebral O2 saturation integrates the arterial O2 content and the cerebral perfusion, and as established for skeletal muscle, NIRS obtains information on tissue oxygenation and metabolism beyond that obtained by venous blood sampling. Caveats of cerebral NIRS include insufficient light shielding, optode displacement and a sample volume including muscle or the frontal sinus mucous membrane. The relative influence from the extracranial tissue is minimized by optode separation and correction for an extracranial sample volume, or both. The natural pigment melatonin and also water are of little influence to spectroscopic analysis of cerebral oxygenation, whereas bilirubin systematically lowers ScO2 and attenuates the detection of changes in cerebral oxygenation. By NIRS, reduction of cytochrome oxidase is demonstrated during hypoxic hypoxaemia and head-up tilt-induced arterial hypotension, but the changes are small. In the clinical setting, NIRS offers useful information in patients with both systemic and local cerebral circulatory impairment, for example, during cranial trauma, surgery on the cerebral arteries, orthostasis and acute heart failure. Whereas mapping of the brain circulation is needed for jugular venous sampling to reflect either global or local oxygenation, the determination of cerebral oxygenation by NIRS has the advantage of localized monitoring of the cerebral cortex.
近红外（IR）光能够轻松穿透生物组织，而脑氧合的体内光谱所提供的信息详细且具有高时间分辨率。近红外光谱（NIRS）可反映动脉低血压、低氧性低氧血症以及低碳酸血症和高碳酸血症期间的脑氧合情况。通过双波长NIRS测定，脑氧饱和度整合了动脉氧含量和脑灌注，并且如同在骨骼肌中所证实的那样，NIRS获取的关于组织氧合和代谢的信息超出了静脉血采样所获得的信息。脑NIRS的注意事项包括遮光不足、光极移位以及包含肌肉或额窦黏膜的样本体积。通过光极分离以及对颅外样本体积进行校正，或者二者同时进行，可将颅外组织的相对影响降至最低。天然色素褪黑素以及水对脑氧合的光谱分析影响较小，而胆红素会系统性地降低脑氧饱和度（ScO2）并减弱对脑氧合变化的检测。通过NIRS可证实在低氧性低氧血症和头高位倾斜引起的动脉低血压期间细胞色素氧化酶减少，但变化较小。在临床环境中，NIRS为患有全身性和局部脑循环障碍的患者提供有用信息，例如在颅脑创伤、脑动脉手术、直立性低血压和急性心力衰竭期间。虽然颈静脉采样需要绘制脑循环图以反映整体或局部氧合情况，但通过NIRS测定脑氧合具有对大脑皮层进行局部监测的优势。
