Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy; Department of Anaesthesiology and Intensive Care Medicine, Medical University Innsbruck, Innsbruck, Austria.
Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy.
Resuscitation. 2021 Jan;158:175-182. doi: 10.1016/j.resuscitation.2020.11.023. Epub 2020 Nov 26.
A sufficient supply of oxygen is crucial to avoid hypoxic cardiac arrest and brain damage within 30 min in completely-buried avalanche victims. Snow density influences levels of hypoxia and hypercapnia. The goal of this study was to investigate the effects of hypoxia and hypercapnia on cerebral oxygenation (ScO) in humans breathing into an artificial air pocket.
Each subject breathed into a closed system (air-tight face mask - plastic tube - snow air-pocket of 4 L) up to 30 min. Each subject performed three tests in different snow densities. ScO was measured by a near-infrared spectroscopy (NIRS) device. Measurements included peripheral oxygen saturation (SpO), end-tidal carbon dioxide (ETCO), air pocket gases and blood gases. Snow density was assessed via standard methods and micro-computed tomography. Based on predetermined criteria, tests were classified based on whether they were terminated before 30 min and the reason for termination. The categories were: completed tests (30 min), tests terminated before 30 min when SpO dropped to ≤75% and tests that were terminated before 30 min by requests of the subjects. General linear models were used to compare termination groups for changes in ScO, ETCO, SpO and air pocket gases, and a multivariate analysis was used to detect factor independent effects on ScO.
ScO was decreased in the group in which the tests were terminated for SpO ≤ 75% caused by a decrease in oxygen supply in high snow densities. In the completed tests, an increase in ScO occurred despite decreased oxygen supply and decreased carbon dioxide removal.
Our data show that ScO determined by NIRS was not always impaired in humans breathing into an artificial air pocket despite decreased oxygen supply and decreased carbon dioxide removal. This may indicate that in medium to low snow densities brain oxygenation can be sufficient, which may reflect the initial stage of the triple H (hypothermia, hypoxia, and hypercapnia) syndrome. In high snow densities, ScO showed a significant decrease caused by a critical decrease in oxygen supply. This could lead to a higher risk of hypoxic cardiac arrest and brain damage.
在完全被埋的雪崩受害者中，30 分钟内避免缺氧性心脏骤停和脑损伤需要充足的氧气供应。雪的密度会影响缺氧和高碳酸血症的程度。本研究的目的是调查在人工气袋中呼吸时缺氧和高碳酸血症对人脑氧合（ScO）的影响。
每个受试者在 30 分钟内通过封闭系统（气密面罩-塑料管-4L 雪气袋）呼吸。每个受试者在不同的雪密度下进行三次测试。ScO 通过近红外光谱（NIRS）设备进行测量。测量包括外周血氧饱和度（SpO）、呼气末二氧化碳（ETCO）、气袋气体和血气。雪密度通过标准方法和微计算机断层扫描进行评估。根据预定标准，根据是否在 30 分钟前结束以及结束的原因对测试进行分类。类别包括：完成的测试（30 分钟）、SpO 降至≤75%时在 30 分钟前结束的测试和受试者要求在 30 分钟前结束的测试。使用一般线性模型比较终止组的 ScO、ETCO、SpO 和气袋气体的变化，并使用多元分析检测对 ScO 有独立影响的因素。
在 SpO 降至≤75%导致高雪密度下供氧减少的终止组中，ScO 降低。在完成的测试中，尽管供氧减少，二氧化碳去除减少，但 ScO 增加。
我们的数据表明，尽管供氧减少和二氧化碳去除减少，通过 NIRS 确定的 ScO 在人类呼吸人工气袋时并不总是受损。这可能表明在中低雪密度下，脑氧合可能足够，这可能反映了三重 H（低温、缺氧和高碳酸血症）综合征的初始阶段。在高雪密度下，由于供氧严重减少，ScO 显著降低。这可能导致缺氧性心脏骤停和脑损伤的风险增加。
