We hypothesized that as CARDS may present different pathophysiological features than classic ARDS, the application of high levels of end-expiratory pressure is questionable. Our first aim was to investigate the effects of 5–15 cmH2O of PEEP on partitioned respiratory mechanics, gas exchange and dead space; secondly, we investigated whether respiratory system compliance and severity of hypoxemia could affect the response to PEEP on partitioned respiratory mechanics, gas exchange and dead space, dividing the population according to the median value of respiratory system compliance and oxygenation. Thirdly, we explored the effects of an additional PEEP selected according to the Empirical PEEP-FiO2 table of the EPVent-2 study on partitioned respiratory mechanics and gas exchange in a subgroup of patients. Sixty-one paralyzed mechanically ventilated patients with a confirmed diagnosis of SARS-CoV-2 were enrolled (age 60 [54–67] years, PaO2/FiO2 113 [79–158] mmHg and PEEP 10 [10–10] cmH2O). Keeping constant tidal volume, respiratory rate and oxygen fraction, two PEEP levels (5 and 15 cmH2O) were selected. In a subgroup of patients an additional PEEP level was applied according to an Empirical PEEP-FiO2 table (empirical PEEP). At each PEEP level gas exchange, partitioned lung mechanics and hemodynamic were collected. At 15 cmH2O of PEEP the lung elastance, lung stress and mechanical power were higher compared to 5 cmH2O. The PaO2/FiO2, arterial carbon dioxide and ventilatory ratio increased at 15 cmH2O of PEEP. The arterial–venous oxygen difference and central venous saturation were higher at 15 cmH2O of PEEP. Both the mechanics and gas exchange variables significantly increased although with high heterogeneity. By increasing the PEEP from 5 to 15 cmH2O, the changes in partitioned respiratory mechanics and mechanical power were not related to hypoxemia or respiratory compliance. The empirical PEEP was 18 ± 1 cmH2O. The empirical PEEP significantly increased the PaO2/FiO2 but also driving pressure, lung elastance, lung stress and mechanical power compared to 15 cmH2O of PEEP. In COVID-19 ARDS during the early phase the effects of raising PEEP are highly variable and cannot easily be predicted by respiratory system characteristics, because of the heterogeneity of the disease.

中文翻译：

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COVID-19 急性呼吸窘迫综合征的呼气末正压：异质效应

我们假设由于 CARDS 可能呈现出与经典 ARDS 不同的病理生理特征，因此应用高水平呼气末压力是有问题的。我们的第一个目标是研究 5-15 cmH2O 的 PEEP 对分区呼吸力学、气体交换和死腔的影响；其次，我们研究了呼吸系统顺应性和低氧血症的严重程度是否会影响对 PEEP 对分区呼吸力学、气体交换和死腔的反应，根据呼吸系统顺应性和氧合的中值划分人群。第三，我们探讨了根据 EPVent-2 研究的经验 PEEP-FiO2 表选择的额外 PEEP 对部分患者的分区呼吸力学和气体交换的影响。招募了 61 名确诊为 SARS-CoV-2 的瘫痪机械通气患者（年龄 60 [54-67] 岁，PaO2/FiO2 113 [79-158] mmHg 和 PEEP 10 [10-10] cmH2O）。保持恒定的潮气量、呼吸频率和氧气分数，选择了两个 PEEP 水平（5 和 15 cmH2O）。在一组患者中，根据经验 PEEP-FiO2 表（经验 PEEP）应用了额外的 PEEP 水平。在每个 PEEP 水平的气体交换中，收集分区肺力学和血流动力学。在 15 cmH2O 的 PEEP 下，与 5 cmH2O 相比，肺弹性、肺应力和机械功率更高。在 PEEP 为 15 cmH2O 时，PaO2/FiO2、动脉二氧化碳和通气比增加。PEEP 为 15 cmH2O 时，动静脉血氧差和中心静脉饱和度较高。尽管具有高度异质性，但力学和气体交换变量均显着增加。通过将 PEEP 从 5 cmH2O 增加到 15 cmH2O，分配的呼吸力学和机械功率的变化与低氧血症或呼吸顺应性无关。经验 PEEP 为 18 ± 1 cmH2O。与 15 cmH2O 的 PEEP 相比，经验 PEEP 显着增加了 PaO2/FiO2，但也增加了驱动压力、肺弹性、肺应力和机械功率。在早期阶段的 COVID-19 ARDS 中，由于疾病的异质性，提高 PEEP 的影响变化很大，并且无法通过呼吸系统特征轻易预测。分区呼吸力学和机械功率的变化与低氧血症或呼吸顺应性无关。经验 PEEP 为 18 ± 1 cmH2O。与 15 cmH2O 的 PEEP 相比，经验 PEEP 显着增加了 PaO2/FiO2，但也增加了驱动压力、肺弹性、肺应力和机械功率。在早期阶段的 COVID-19 ARDS 中，由于疾病的异质性，提高 PEEP 的影响变化很大，并且无法通过呼吸系统特征轻易预测。分区呼吸力学和机械功率的变化与低氧血症或呼吸顺应性无关。经验 PEEP 为 18 ± 1 cmH2O。与 15 cmH2O 的 PEEP 相比，经验 PEEP 显着增加了 PaO2/FiO2，但也增加了驱动压力、肺弹性、肺应力和机械功率。在早期阶段的 COVID-19 ARDS 中，由于疾病的异质性，提高 PEEP 的影响变化很大，并且无法通过呼吸系统特征轻易预测。