The optimal level of positive end-expiratory pressure (PEEP) during mechanical ventilation for COVID-19 pneumonia remains debated and should ideally be guided by responses in both lung volume and perfusion. Capnodynamic monitoring allows both end-expiratory lung volume ( $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ ) and effective pulmonary blood flow (EPBF) to be determined at the bedside with ongoing ventilation. Patients with COVID-19-related moderate to severe respiratory failure underwent capnodynamic monitoring of $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ and EPBF during a step increase in PEEP by 50% above the baseline (PEEPlow to PEEPhigh). The primary outcome was a > 20 mm Hg increase in arterial oxygen tension to inspired fraction of oxygen (P/F) ratio to define responders versus non-responders. Secondary outcomes included changes in physiological dead space and correlations with independently determined recruited lung volume and the recruitment-to-inflation ratio at an instantaneous, single breath decrease in PEEP. Mixed factor ANOVA for group mean differences and correlations by Pearson’s correlation coefficient are reported including their 95% confidence intervals. Of 27 patients studied, 15 responders increased the P/F ratio by 55 [24–86] mm Hg compared to 12 non-responders (p < 0.01) as PEEPlow (11 ± 2.7 cm H2O) was increased to PEEPhigh (18 ± 3.0 cm H2O). The $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ was 461 [82–839] ml less in responders at PEEPlow (p = 0.02) but not statistically different between groups at PEEPhigh. Responders increased both $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ and EPBF at PEEPhigh (r = 0.56 [0.18–0.83], p = 0.03). In contrast, non-responders demonstrated a negative correlation (r = − 0.65 [− 0.12 to − 0.89], p = 0.02) with increased lung volume associated with decreased pulmonary perfusion. Decreased (− 0.06 [− 0.02 to − 0.09] %, p < 0.01) dead space was observed in responders. The change in $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ correlated with both the recruited lung volume (r = 0.85 [0.69–0.93], p < 0.01) and the recruitment-to-inflation ratio (r = 0.87 [0.74–0.94], p < 0.01). In mechanically ventilated patients with moderate to severe COVID-19 respiratory failure, improved oxygenation in response to increased PEEP was associated with increased end-expiratory lung volume and pulmonary perfusion. The change in end-expiratory lung volume was positively correlated with the lung volume recruited and the recruitment-to-inflation ratio. This study demonstrates the feasibility of capnodynamic monitoring to assess physiological responses to PEEP at the bedside to facilitate an individualised setting of PEEP. Trial registration: NCT05082168 (18th October 2021).

中文翻译：

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中度至重度 COVID-19 肺炎中呼气末正压升高对肺容积和血流量的二氧化碳动力学监测：一项观察性研究

COVID-19 肺炎机械通气期间呼气末正压 (PEEP) 的最佳水平仍有争议，理想情况下应以肺容量和灌注反应为指导。二氧化碳动力学监测允许在持续通风的床边。与 COVID-19 相关的中度至重度呼吸衰竭患者在逐步增加期间接受了 $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ 和 EPBF 的二氧化碳动力学监测。 PEEP 比基线高 50%（PEEPlow 到 PEEPhigh）。主要结果是动脉氧分压与吸入氧分数 (P/F) 的比值增加 > 20 mm Hg，以确定有反应者与无反应者。次要结果包括生理死腔的变化以及与独立确定的肺复张量的相关性，以及在 PEEP 瞬时单次呼吸降低时的肺复张与充气比率的相关性。报告了 Pearson 相关系数的组平均差异和相关性的混合因子 ANOVA，包括它们的 95% 置信区间。在研究的 27 名患者中，当 PEEPlow (11 ± 2.7 cm H2O) 增加到 PEEPhigh (18 ± 3.0厘米水柱）。PEEPlow 响应者的 $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ 减少了 461 [82–839] ml（p = 0.02），但没有统计学差异在 PEEPhigh 组之间。响应者在 PEEPhigh 时增加了 $${\text{EELV}}_{{{\text{CO}}_{2} }}$$ 和 EPBF（r = 0.56 [0.18–0.83]，p = 0。03)。相反，无反应者表现出与肺灌注减少相关的肺容量增加呈负相关（r = - 0.65 [- 0.12 至 - 0.89]，p = 0.02）。在响应者中观察到（- 0.06 [- 0.02 至 - 0.09] %，p < 0.01）死腔减少。$${\text{EELV}}_{{{\text{CO}}_{2} }}$$ 的变化与肺复张量相关（r = 0.85 [0.69–0.93]，p < 0.01 ) 和招聘与通胀比率 (r = 0.87 [0.74–0.94], p < 0.01)。在中度至重度 COVID-19 呼吸衰竭的机械通气患者中，响应于 PEEP 增加的氧合改善与呼气末肺容量和肺灌注增加有关。呼气末肺容积的变化与肺复张量和肺复张与充气比率呈正相关。这项研究证明了二氧化碳动力学监测在床边评估对 PEEP 的生理反应以促进 PEEP 的个性化设置的可行性。试用注册：NCT05082168（2021 年 10 月 18 日）。