急性呼吸窘迫综合征死腔量与潮气量比值的经验估计的有效性。

Validity of Empirical Estimates of the Ratio of Dead Space to Tidal Volume in ARDS.

机构信息

Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Canada.

Department of Medicine, Division of Respirology, University Health Network, Toronto, Canada.

出版信息

Respir Care. 2021 Apr;66(4):559-565. doi: 10.4187/respcare.08246. Epub 2020 Oct 20.

DOI:10.4187/respcare.08246

PMID:33082218

Abstract

BACKGROUND

The ratio of dead space to tidal volume (V/V) is a clinically relevant parameter in ARDS; it has been shown to predict mortality, and it determines the extent to which extracorporeal CO removal reduces tidal volume (V) and driving pressure (ΔP). V/V can be estimated with volumetric capnography, but empirical formulas using demographic and physiological information have been proposed to estimate V/V without the need of additional equipment. It is unknown whether estimated and measured V/V produce similar estimates of the predicted effect of extracorporeal CO removal on ΔP.

METHODS

We performed a secondary analysis of data from a previous clinical trial including subjects with ARDS in whom V/V and CO production ([Formula: see text]) were measured with volumetric capnography. The estimated ratio of dead space to tidal volume (V/V) was calculated using standard empiric formulas. Agreement between measured and estimated values was evaluated with Bland-Altman analysis. Agreement between the predicted change in ΔP with extracorporeal CO removal as computed using the measured ratio of alveolar dead space to tidal volume (V/V) or estimated V/V (V/V) was also evaluated.

RESULTS

V/V was higher than measured V/V, and agreement between them was low (bias 0.05, limits of agreement -0.21 to 0.31). Differences between measured and estimated [Formula: see text] accounted for 57% of the error in V/V. The predicted reduction in ΔP with extracorporeal CO removal computed using V/V was in reasonable agreement with the expected reduction using V/V (bias -0.7 cm HO, limits of agreement -1.87 to 0.47 cm HO). In multivariable regression, measured V/V was associated with mortality (odds ratio 1.9, 95% CI 1.2-3.1, = .01), but V/V was not (odds ratio 1.2, 95% CI 0.8-1.8, = .3).

CONCLUSIONS

V/V and V/V showed low levels of agreement and cannot be used interchangeably in clinical practice. Nevertheless, the predicted decrease in ΔP due to extracorporeal CO removal was similar when computed from either estimated or measured V/V.

摘要

背景

死腔与潮气量之比（V/V）是 ARDS 中一个有临床意义的参数；它已被证明可预测死亡率，并决定了体外 CO 去除降低潮气量（V）和驱动压（ΔP）的程度。V/V 可以通过容积碳酸图来估计，但已经提出了使用人口统计学和生理学信息的经验公式来估计 V/V，而无需额外的设备。尚不清楚估计和测量的 V/V 是否会产生类似的体外 CO 去除对ΔP 的预测效果的估计。

方法

我们对先前临床试验的数据进行了二次分析，该试验包括患有 ARDS 的患者，他们的 V/V 和 CO 生成量([Formula: see text])通过容积碳酸图进行了测量。使用标准经验公式计算估计的死腔与潮气量之比（V/V）。通过 Bland-Altman 分析评估测量值和估计值之间的一致性。还评估了使用测量的肺泡死腔与潮气量之比（V/V）或估计的 V/V（V/V）计算的体外 CO 去除对ΔP 的预测变化之间的一致性。

结果

V/V 高于测量的 V/V，两者之间的一致性较低（偏差 0.05，一致性界限 -0.21 至 0.31）。测量和估计的[Formula: see text]之间的差异占 V/V 误差的 57%。使用 V/V 计算的体外 CO 去除对ΔP 的预测降低与使用 V/V 的预期降低基本一致（偏差 -0.7 cm HO，一致性界限 -1.87 至 0.47 cm HO）。在多变量回归中，测量的 V/V 与死亡率相关（比值比 1.9，95%CI 1.2-3.1， =.01），但 V/V 没有（比值比 1.2，95%CI 0.8-1.8， =.3）。