Background

Ventilation/perfusion inequalities impair gas exchange in acute respiratory distress syndrome (ARDS). Although increased dead-space ventilation (V_D/V_T) has been described in ARDS, its mechanism is not clearly understood. We sought to evaluate the relationships between dynamic variations in V_D/V_T and extra-pulmonary microcirculatory blood flow detected at sublingual mucosa hypothesizing that an altered microcirculation, which is a generalized phenomenon during severe inflammatory conditions, could influence ventilation/perfusion mismatching manifested by increases in V_D/V_T fraction during early stages of ARDS.

Methods

Forty-two consecutive patients with early moderate and severe ARDS were included. PEEP was set targeting the best respiratory-system compliance after a PEEP-decremental recruitment maneuver. After 60 min of stabilization, hemodynamics and respiratory mechanics were recorded and blood gases collected. V_D/V_T was calculated from the CO₂ production (\(V_{{{\text{CO}}_{2} }}\)) and CO₂ exhaled fraction (\(F_{{{\text{ECO}}_{2} }}\)) measurements by volumetric capnography. Sublingual microcirculatory images were simultaneously acquired using a sidestream dark-field device for an ulterior blinded semi-quantitative analysis. All measurements were repeated 24 h after.

Results

Percentage of small vessels perfused (PPV) and microcirculatory flow index (MFI) were inverse and significantly related to V_D/V_T at baseline (Spearman’s rho = − 0.76 and − 0.63, p < 0.001; R² = 0.63, and 0.48, p < 0.001, respectively) and 24 h after (Spearman’s rho = − 0.71, and − 0.65; p < 0.001; R² = 0.66 and 0.60, p < 0.001, respectively). Other respiratory, macro-hemodynamic and oxygenation parameters did not correlate with V_D/V_T. Variations in PPV between baseline and 24 h were inverse and significantly related to simultaneous changes in V_D/V_T (Spearman’s rho = − 0.66, p < 0.001; R² = 0.67, p < 0.001).

Conclusion

Increased heterogeneity of microcirculatory blood flow evaluated at sublingual mucosa seems to be related to increases in V_D/V_T, while respiratory mechanics and oxygenation parameters do not. Whether there is a cause–effect relationship between microcirculatory dysfunction and dead-space ventilation in ARDS should be addressed in future research.

中文翻译：

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早期ARDS的微循环功能障碍和死腔通气：一项基于假设的观察性研究

背景

通气/灌注不均会损害急性呼吸窘迫综合征（ARDS）中的气体交换。尽管ARDS中描述了增加的死角通气量（V _D / V _T），但其机理尚不清楚。我们试图评估V _D / V _T的动态变化与舌下粘膜下检测到的肺外微循环血流量之间的关系，认为微循环改变是严重炎症条件下的普遍现象，可能影响通气/灌注失配，表现为增加V _d / V _Ť 在ARDS早期阶段的比例较低。

方法

连续纳入了42例早期中重度ARDS患者。在PEEP减少招募策略后，PEEP的目标是达到最佳的呼吸系统顺应性。稳定60分钟后，记录血液动力学和呼吸力学并收集血气。V _D / V _T由CO ₂产生量（\（V _ {{{text {CO}} _ {2}}} \））和CO ₂呼出分数（\（F _ {{{\ text {ECO }} _ {2}}} \））通过体积二氧化碳图进行测量。使用侧流暗场设备同时采集舌下微循环图像，以进行下眼盲的半定量分析。24小时后重复所有测量。

结果

灌注的小血管百分比（PPV）和微循环流量指数（MFI）与基线时的V _D / V _T呈负相关（Spearman's rho = − 0.76和− 0.63，p  <0.001；R ²  = 0.63和0.48， 分别为p <0.001和24小时后（Spearman的rho =-0.71和-0.65; p  <0.001; R ²  = 0.66和0.60，p  <0.001）。其他呼吸，宏观血液动力学和氧合参数与V _D / V _T不相关。基线和24 h之间PPV的变化是相反的，并且与V _D / V _T的同时变化显着相关（Spearman的rho = − 0.66，p  <0.001；R ²  = 0.67，p  <0.001）。

结论

在舌下粘膜处评估的微循环血流异质性增加似乎与V _D / V _T的增加有关，而呼吸力学和氧合参数却不相关。ARDS中微循环功能障碍与死腔通气之间是否存在因果关系，应在以后的研究中解决。