The Ritchie Centre, Monash Institute of Medical Research, Monash University, Melbourne, Victoria, Australia.
Anesthesiology. 2010 Dec;113(6):1385-91. doi: 10.1097/ALN.0b013e3181fc5567.
Bedside assessments of cerebral oxygenation are sought to monitor cerebral injury in patients undergoing intensive care. Spatially resolved spectroscopy measures tissue oxygenation index (TOI, %) which reflects mixed cerebral arterial and venous oxygenations. We aimed to evaluate arterial and venous components of TOI (cerebral arterial to venous volume ratio [A:V ratio]) in the newborn lamb brain using cerebral arterial and venous blood samples, and to investigate the impact of acute hypoxemia on the A:V ratio and TOI.
Nine lambs were ventilated with varied inspired oxygen to generate arterial oxygen saturations between 25% and 100%. Cerebral arterial and venous oxygen saturations analyzed using cooximeter of arterial and superior sagittal sinus blood were used to estimate TOI (TOIcox), assuming cerebral A:V ratio of 25:75. TOIcox was compared with the TOI measured by spatially resolved spectroscopy (TOIsrs). Actual cerebral arterial and venous volume fractions were reestimated using TOIsrs = cerebral arterial volume fraction cerebral arterial oxygen saturation + cerebral venous volume fraction*cerebral venous oxygen saturation.
Median (range) TOIsrs was 48.5% (32.0-64.1%), and TOIcox was 48.4% (13.7-74.4%), and the two were significantly correlated (R = 0.77). The mean difference between TOIsrs and TOIcox was 2.4% (limits of agreement ± 18.1%). The TOIsrs - TOIcox difference varied with oxygen saturations, with TOIsrs higher than TOIcox at low saturations, and lower at high saturations. Cerebral arterial volume fraction was 22.9-27.5% in normoxia and markedly increased in hypoxemia.
TOI corresponds with cerebral oxygenation. The variable agreement of TOIsrs with TOIcox may reflect changes in cerebral A:V ratio due to arterial oxygenation-related vasoreactivity.
在接受重症监护的患者中，人们寻求床边评估脑氧合情况以监测脑损伤。空间分辨光谱测量组织氧合指数（TOI，%），反映混合性脑动脉和静脉氧合情况。我们旨在使用脑动脉和静脉血样评估新生羔羊脑的 TOI 的动脉和静脉成分（脑动脉与静脉容积比[A:V 比]），并研究急性低氧血症对 A:V 比和 TOI 的影响。
9 只羔羊在不同的吸入氧浓度下通气，以产生动脉血氧饱和度在 25%至 100%之间的变化。使用动脉和矢状窦上的血气分析仪分析动脉和静脉血氧饱和度，以估计 TOI（TOIcox），假设脑 A:V 比为 25:75。TOIcox 与空间分辨光谱测量的 TOI（TOIsrs）进行比较。使用 TOIsrs = 脑动脉容积分数×脑动脉血氧饱和度+脑静脉容积分数×脑静脉血氧饱和度重新估计实际的脑动脉和静脉容积分数。
中位数（范围）TOIsrs 为 48.5%（32.0-64.1%），TOIcox 为 48.4%（13.7-74.4%），两者呈显著相关（R = 0.77）。TOIsrs 和 TOIcox 之间的平均差异为 2.4%（一致性界限±18.1%）。TOIsrs-TOIcox 差异随氧饱和度而变化，在低饱和度时 TOIsrs 高于 TOIcox，在高饱和度时则较低。在正常氧合时，脑动脉容积分数为 22.9%-27.5%，在低氧血症时明显增加。
TOI 与脑氧合相关。TOIsrs 与 TOIcox 的可变一致性可能反映了由于动脉氧合相关血管反应性导致的脑 A:V 比的变化。
