BACKGROUND The mechanisms underlying oxygenation improvement after prone positioning in COVID-19 acute respiratory distress syndrome have not been fully elucidated yet. The authors hypothesized that the oxygenation increase with prone positioning is secondary to the improvement of ventilation-perfusion matching. METHODS In a series of consecutive intubated COVID-19 acute respiratory distress syndrome patients receiving volume-controlled ventilation, the authors prospectively assessed the percent variation of ventilation-perfusion matching by electrical impedance tomography before and 90 min after the first cycle of prone positioning (primary endpoint). The authors also assessed changes in the distribution and homogeneity of lung ventilation and perfusion, lung overdistention and collapse, respiratory system compliance, driving pressure, optimal positive end-expiratory pressure, as assessed by electrical impedance tomography, and the ratio of partial pressure to fraction of inspired oxygen (Pao2/Fio2; secondary endpoints). Data are reported as medians [25th to 75th] or percentages. RESULTS The authors enrolled 30 consecutive patients, all analyzed without missing data. Compared to the supine position, prone positioning overall improved ventilation-perfusion matching from 58% [43 to 69%] to 68% [56 to 75%] (P = 0.042), with a median difference of 8.0% (95% CI, 0.1 to 16.0%). Dorsal ventilation increased from 39% [31 to 43%] to 52% [44 to 62%] (P < 0.001), while dorsal perfusion did not significantly vary. Prone positioning also reduced lung overdistension from 9% [4 to 11%] to 4% [2 to 6%] (P = 0.025), while it did not significantly affect ventilation and perfusion homogeneity, lung collapse, static respiratory system compliance, driving pressure, and optimal positive end-expiratory pressure. Pao2/Fio2 overall improved from 141 [104 to 182] mmHg to 235 [164 to 267] mmHg (P = 0.019). However, 9 (30%) patients were nonresponders, experiencing an increase in Pao2/Fio2 less than 20% with respect to baseline. CONCLUSIONS In COVID-19 acute respiratory distress syndrome patients, prone positioning overall produced an early increase in ventilation-perfusion matching and dorsal ventilation. These effects were, however, heterogeneous among patients. EDITOR’S PERSPECTIVE

中文翻译：

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俯卧位对 COVID-19 急性呼吸窘迫综合征的早期生理影响。

背景 COVID-19 急性呼吸窘迫综合征俯卧位后氧合改善的潜在机制尚未完全阐明。作者假设俯卧位的氧合增加是通气-灌注匹配改善的次要因素。方法 在一系列接受容量控制通气的连续插管 COVID-19 急性呼吸窘迫综合征患者中，作者前瞻性地评估了俯卧位第一个周期之前和之后 90 分钟（主要端点）。作者还评估了肺通气和灌注分布和均匀性、肺过度扩张和塌陷、呼吸系统顺应性、驱动压、通过电阻抗断层扫描评估的最佳呼气末正压，以及分压与吸入氧气分数的比率（Pao2/FiO2；次要终点）。数据报告为中位数 [第 25 位至第 75 位] 或百分比。结果 作者招募了 30 名连续的患者，所有患者都进行了分析，没有遗漏数据。与仰卧位相比，俯卧位整体通气-灌注匹配率从 58% [43% 至 69%] 提高到 68% [56% 至 75%] (P = 0.042)，中位差异为 8.0%（95% CI， 0.1 至 16.0%）。背部通气从 39% [31% 至 43%] 增加到 52% [44% 至 62%] (P < 0.001)，而背部灌注没有显着变化。俯卧位还将肺过度扩张从 9% [4% 至 11%] 降低至 4% [2% 至 6%] (P = 0.025)，同时它对通气和灌注均匀性没有显着影响，肺萎陷、静态呼吸系统顺应性、驱动压和最佳呼气末正压。Pao2/FiO2 整体从 141 [104 至 182] mmHg 改善至 235 [164 至 267] mmHg (P = 0.019)。然而，9 名 (30%) 患者无反应，与基线相比，Pao2/FiO2 增加不到 20%。结论 在 COVID-19 急性呼吸窘迫综合征患者中，俯卧位总体上产生了通气-灌注匹配和背侧通气的早期增加。然而，这些影响在患者中存在异质性。编辑的观点 与基线相比，Pao2/FiO2 增加不到 20%。结论 在 COVID-19 急性呼吸窘迫综合征患者中，俯卧位总体上产生了通气-灌注匹配和背侧通气的早期增加。然而，这些影响在患者中存在异质性。编辑的观点 与基线相比，Pao2/FiO2 增加不到 20%。结论 在 COVID-19 急性呼吸窘迫综合征患者中，俯卧位总体上产生了通气-灌注匹配和背侧通气的早期增加。然而，这些影响在患者中存在异质性。编辑的观点