Prinianakis George, Alexopoulou Christina, Mamidakis Eutichis, Kondili Eumorfia, Georgopoulos Dimitris
Intensive Care Medicine Department, University of Crete, University Hospital of Heraklion, Heraklion, Crete, Greece.
Crit Care. 2005 Feb;9(1):R24-31. doi: 10.1186/cc3012. Epub 2004 Nov 29.
The cuff-leak test has been proposed as a simple method to predict the occurrence of post-extubation stridor. The test is performed by cuff deflation and measuring the expired tidal volume a few breaths later (VT). The leak is calculated as the difference between VT with and without a deflated cuff. However, because the cuff remains deflated throughout the respiratory cycle a volume of gas may also leak during inspiration and therefore this method (conventional) measures the total leak consisting of an inspiratory and expiratory component. The aims of this physiological study were, first, to examine the effects of various variables on total leak and, second, to compare the total leak with that obtained when the inspiratory component was eliminated, leaving only the expiratory leak.
In 15 critically ill patients mechanically ventilated on volume control mode, the cuff-leak volume was measured randomly either by the conventional method (Leakconv) or by deflating the cuff at the end of inspiration and measuring the VT of the following expiration (Leakpause). To investigate the effects of respiratory system mechanics and inspiratory flow, cuff-leak volume was studied by using a lung model, varying the cross-sectional area around the endotracheal tube and model mechanics.
In patients Leakconv was significantly higher than Leakpause, averaging 188 +/- 159 ml (mean +/- SD) and 61 +/- 75 ml, respectively. In the model study Leakconv increased significantly with decreasing inspiratory flow and model compliance. Leakpause and Leakconv increased slightly with increasing model resistance, the difference being significant only for Leakpause. The difference between Leakconv and Leakpause increased significantly with decreasing inspiratory flow (V'I) and model compliance and increasing cross-sectional area around the tube.
We conclude that the cross-sectional area around the endotracheal tube is not the only determinant of the cuff-leak test. System compliance and inspiratory flow significantly affect the test, mainly through an effect on the inspiratory component of the total leak. The expiratory component is slightly influenced by respiratory system resistance.
套囊漏气试验被认为是预测拔管后喘鸣发生的一种简单方法。该试验通过放气套囊并在数呼吸后测量呼出潮气量（VT）来进行。漏气量通过有或无放气套囊时的VT差值来计算。然而，由于套囊在整个呼吸周期中保持放气状态，吸气时也可能有一定量的气体泄漏，因此这种方法（传统方法）测量的是由吸气和呼气成分组成的总漏气量。本生理学研究的目的，一是研究各种变量对总漏气量的影响，二是将总漏气量与消除吸气成分后仅测量呼气漏气量时得到的结果进行比较。
对15例接受容量控制模式机械通气的重症患者，随机采用传统方法（Leakconv）或在吸气末放气套囊并测量随后呼气的VT（Leakpause）来测量套囊漏气量。为研究呼吸系统力学和吸气流量的影响，通过使用肺模型、改变气管导管周围的横截面积和模型力学来研究套囊漏气量。
在患者中，Leakconv显著高于Leakpause，平均分别为188±159 ml（均值±标准差）和61±75 ml。在模型研究中，Leakconv随吸气流量和模型顺应性的降低而显著增加。Leakpause和Leakconv随模型阻力增加略有增加，仅Leakpause的差异有统计学意义。Leakconv与Leakpause之间的差异随吸气流量（V'I）和模型顺应性的降低以及气管导管周围横截面积的增加而显著增大。
我们得出结论，气管导管周围的横截面积不是套囊漏气试验的唯一决定因素。系统顺应性和吸气流量对试验有显著影响，主要是通过对总漏气量的吸气成分产生影响。呼气成分受呼吸系统阻力的影响较小。
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