End-expiratory lung volume (EELV) is reduced in mechanically ventilated patients, especially in pathologic conditions. The resulting heterogeneous distribution of ventilation increases the risk for ventilation induced lung injury. Clinical measurement of EELV however, remains difficult. Validation of a novel continuous capnodynamic method based on expired carbon dioxide (CO2) kinetics for measuring EELV in mechanically ventilated critically-ill patients. Prospective study of mechanically ventilated patients scheduled for a diagnostic computed tomography exploration. Comparisons were made between absolute and corrected EELVCO2 values, the latter accounting for the amount of CO2 dissolved in lung tissue, with the reference EELV measured by computed tomography (EELVCT). Uncorrected and corrected EELVCO2 was compared with total CT volume (density compartments between − 1000 and 0 Hounsfield units (HU) and functional CT volume, including density compartments of − 1000 to − 200HU eliminating regions of increased shunt. We used comparative statistics including correlations and measurement of accuracy and precision by the Bland Altman method. Of the 46 patients included in the final analysis, 25 had a diagnosis of ARDS (24 of which COVID-19). Both EELVCT and EELVCO2 were significantly reduced (39 and 40% respectively) when compared with theoretical values of functional residual capacity (p < 0.0001). Uncorrected EELVCO2 tended to overestimate EELVCT with a correlation r2 0.58; Bias − 285 and limits of agreement (LoA) (+ 513 to − 1083; 95% CI) ml. Agreement improved for the corrected EELVCO2 to a Bias of − 23 and LoA of (+ 763 to − 716; 95% CI) ml. The best agreement of the method was obtained by comparison of corrected EELVCO2 with functional EELVCT with a r2 of 0.59; Bias − 2.75 (+ 755 to − 761; 95% CI) ml. We did not observe major differences in the performance of the method between ARDS (most of them COVID related) and non-ARDS patients. In this first validation in critically ill patients, the capnodynamic method provided good estimates of both total and functional EELV. Bias improved after correcting EELVCO2 for extra-alveolar CO2 content when compared with CT estimated volume. If confirmed in further validations EELVCO2 may become an attractive monitoring option for continuously monitor EELV in critically ill mechanically ventilated patients. Trial registration: clinicaltrials.gov (NCT04045262).

中文翻译：

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测量危重患者呼气末肺容量的二氧化碳动力学方法的临床验证

机械通气患者的呼气末肺容积 (EELV) 减少，尤其是在病理情况下。由此产生的通气不均匀分布增加了通气引起的肺损伤的风险。然而，EELV 的临床测量仍然很困难。验证一种基于呼出二氧化碳 (CO2) 动力学的新型连续二氧化碳动力学方法，用于测量机械通气危重患者的 EELV。对计划进行诊断性计算机断层扫描探索的机械通气患者的前瞻性研究。对绝对 EELVCO2 值和校正 EELVCO2 值进行了比较，后者说明了肺组织中溶解的 CO2 量，并与通过计算机断层扫描 (EELVCT) 测量的参考 EELV 进行了比较。将未校正和校正的 EELVCO2 与总 CT 体积（− 1000 至 0 Hounsfield 单位 (HU) 之间的密度区和功能性 CT 体积，包括 − 1000 至 − 200HU 的密度区，消除分流增加的区域）进行比较。我们使用了比较统计数据，包括相关性和最终分析中纳入的 46 名患者中，有 25 名患者诊断为 ARDS（其中 24 名患者为 COVID-19），EELVCT 和 EELVCO2 均显着降低（分别为 39% 和 40%）。与功能残余容量的理论值（p < 0.0001）相比，未校正的 EELVCO2 倾向于高估 EELVCT，相关性 r2 为 0.58；偏差 - 285 和一致性极限 (LoA)（+ 513 至 - 1083；95% CI）ml。校正后的 EELVCO2 的一致性改善至偏差为 − 23，LoA 为（+ 763 至 − 716；95% CI）ml。通过将校正后的 EELVCO2 与 r2 为 0.59 的功能性 EELVCT 进行比较，获得了该方法的最佳一致性；偏差 - 2.75（+ 755 至 - 761；95% CI）ml。我们没有观察到 ARDS（大多数与 COVID 相关）和非 ARDS 患者之间该方法的性能存在重大差异。在危重患者的首次验证中，二氧化碳动力学方法提供了对总 EELV 和功能 EELV 的良好估计。与 CT 估计体积相比，校正肺泡外 CO2 含量的 EELVCO2 后偏差得到改善。如果进一步验证得到证实，EELVCO2 可能成为持续监测危重机械通气患者 EELV 的有吸引力的监测选择。试验注册：clinicaltrials.gov (NCT04045262)​​。