Mutch W Alan C, Duffin James
From the Department of Anesthesiology, Perioperative and Pain Medicine, University of Manitoba (WACM), Canada North Concussion Network, Winnipeg, Manitoba (WACM), Department of Anesthesiology and Pain Medicine, University of Toronto (JD), Thornhill Medical (JD) and Department of Physiology, University of Toronto, Toronto, Ontario, Canada (JD).
Eur J Anaesthesiol. 2022 Sep 1;39(9):774-784. doi: 10.1097/EJA.0000000000001716. Epub 2022 Jul 20.
Regional cerebrovascular reactivity (rCVR) is highly variable in the human brain as measured by blood oxygenation level-dependent (BOLD) MRI to changes in both end-tidal CO 2 and O 2 .
We examined awake participants under carefully controlled end-tidal gas concentrations to assess how regional CVR changes may present with end-tidal gas changes seen commonly with anaesthesia.
Observational study.
Tertiary care centre, Winnipeg, Canada. The imaging for the study occurred in 2019.
Twelve healthy adult subjects.
Cerebral BOLD response was studied under two end-tidal gas paradigms. First end-tidal oxygen (ETO 2 ) maintained stable whereas ETCO 2 increased incrementally from hypocapnia to hypercapnia (CO 2 ramp); second ETCO 2 maintained stable whereas ETO 2 increased from normoxia to hyperoxia (O 2 ramp). BOLD images were modeled with end-tidal gas sequences split into two equal segments to examine regional CVR.
The voxel distribution comparing hypocapnia to mild hypercapnia and mild hyperoxia (mean F I O 2 = 0.3) to marked hyperoxia (mean F I O 2 = 0.7) were compared in a paired fashion ( P < 0.005 to reach threshold for voxel display). Additionally, type analysis was conducted on CO 2 ramp data. This stratifies the BOLD response to the CO 2 ramp into four categories of CVR slope based on segmentation (type A; +/+slope: normal response, type B +/-, type C -/-: intracranial steal, type D -/+.) Types B to D represent altered responses to the CO 2 stimulus.
Differential regional responsiveness was seen for both end-tidal gases. Hypocapnic regional CVR was more marked than hypercapnic CVR in 0.3% of voxels examined ( P < 0.005, paired comparison); the converse occurred in 2.3% of voxels. For O 2 , mild hyperoxia had more marked CVR in 0.2% of voxels compared with greater hyperoxia; the converse occurred in 0.5% of voxels. All subjects had altered regional CO 2 response based on Type Analysis ranging from 4 ± 2 to 7 ± 3% of voxels.
In awake subjects, regional differences and abnormalities in CVR were observed with changes in end-tidal gases common during the conduct of anaesthesia. On the basis of these findings, consideration could be given to minimising regional CVR fluctuations in patients-at-risk of neurological complications by tighter control of end-tidal gases near the individual's resting values.
通过血氧水平依赖（BOLD）磁共振成像（MRI）测量，人类大脑中局部脑血管反应性（rCVR）因呼气末二氧化碳（ETCO₂）和氧气（ETO₂）的变化而高度可变。
我们在精心控制的呼气末气体浓度下检查清醒参与者，以评估局部CVR变化如何随麻醉中常见的呼气末气体变化而呈现。
观察性研究。
加拿大温尼伯的三级护理中心。该研究的成像于2019年进行。
12名健康成年受试者。
在两种呼气末气体模式下研究脑BOLD反应。第一种，呼气末氧（ETO₂）保持稳定，而ETCO₂从低碳酸血症逐渐增加至高碳酸血症（CO₂斜坡）；第二种，ETCO₂保持稳定，而ETO₂从常氧增加至高氧（O₂斜坡）。BOLD图像通过将呼气末气体序列分成两个相等部分进行建模，以检查局部CVR。
以配对方式比较低碳酸血症与轻度高碳酸血症以及轻度高氧（平均FIO₂ = 0.3）与显著高氧（平均FIO₂ = 0.7）时的体素分布（P < 0.005以达到体素显示阈值）。此外，对CO₂斜坡数据进行类型分析。这根据分段将对CO₂斜坡的BOLD反应分为四类CVR斜率（A型；斜率为正/正：正常反应，B型为正/负，C型为负/负：颅内盗血，D型为负/正）。B型至D型代表对CO₂刺激的改变反应。
两种呼气末气体均观察到不同的局部反应性。在所检查的0.3%的体素中，低碳酸血症局部CVR比高碳酸血症CVR更明显（P < 0.005，配对比较）；在2.3%的体素中则相反。对于氧气，与更高程度的高氧相比，轻度高氧在0.2%的体素中具有更明显的CVR；在0.5%的体素中则相反。根据类型分析，所有受试者的局部CO₂反应均有改变，范围为体素的4±2%至7±3%。
在清醒受试者中，观察到麻醉过程中常见的呼气末气体变化会导致CVR的局部差异和异常。基于这些发现，对于有神经并发症风险的患者，可考虑通过更严格地将呼气末气体控制在个体静息值附近，以尽量减少局部CVR波动。
