Department of Anaesthesia and Pain Medicine, University of Edinburgh, Royal Infirmary, 51 Little France Crescent, Edinburgh, UK.
Br J Anaesth. 2012 Nov;109(5):776-81. doi: 10.1093/bja/aes260. Epub 2012 Aug 29.
Using conscious subjects, measurement of the effects of low concentrations of anaesthetic agents can allow the dynamics of onset and offset of the agent to be measured and kinetic values estimated. However, the tests have to be rapid and preferably assess cerebral function.
We used a short version of the digit symbol substitution test (DSST) that allowed frequent measurement of the impairment caused by nitrous oxide. We compared 10 min of onset and offset of breathing 5% and 30% nitrous oxide in 30% oxygen, compared with 30% oxygen only. End-tidal nitrous oxide concentrations were used to predict the concentration in a central compartment, according to a range of T(1/2) values chosen to be consistent with possible cerebral blood flow values.
We studied 19 volunteers and estimated a mean response. Only 30% nitrous oxide decreased the DSST. When DSST scores were related to the values in the predicted central compartment, the best dose-effect relationship was found when the T(1/2) was 37 s, consistent with a regional blood flow of about 120 ml 100 g(-1) min(-1).
The onset of nitrous oxide effect on DSST is rapid, consistent with the perfusion of metabolically active cerebral cortical tissues. The rate of onset is greater than previous measures based on a motor test which involved the function of subcortical structures in the central nervous system.
利用清醒的受试者，可以测量低浓度麻醉剂的作用，从而测量药物的起效和失效动力学，并估计动力学值。然而，这些测试必须快速进行，最好评估大脑功能。
我们使用数字符号替代测试（DSST）的简短版本，该测试可以频繁测量一氧化二氮引起的损害。我们比较了在 30%氧气中呼吸 5%和 30%一氧化二氮 10 分钟的起效和失效，与仅呼吸 30%氧气进行了比较。根据选择的一系列 T(1/2) 值，使用呼气末一氧化二氮浓度来预测中心隔室中的浓度，这些 T(1/2) 值与可能的脑血流值一致。
我们研究了 19 名志愿者并估计了平均反应。只有 30%的一氧化二氮降低了 DSST。当将 DSST 评分与预测中心隔室中的值相关联时，当 T(1/2) 为 37 秒时，发现最佳的剂量-效应关系，这与约 120 ml 100 g(-1) min(-1)的区域血流一致。
一氧化二氮对 DSST 的作用起效迅速，与代谢活跃的皮质脑组织的灌注一致。起效速度大于以前基于涉及中枢神经系统皮质下结构功能的运动测试的测量结果。
