Schumann Stefan, Krappitz Michael, Möller Knut, Hentschel Roland, Braun Günther, Guttmann Josef
Section for Experimental Anesthesiology, University Hospital of Freiburg, Germany.
Respir Physiol Neurobiol. 2008 Jul 31;162(2):132-7. doi: 10.1016/j.resp.2008.05.005. Epub 2008 May 18.
In a physical model of a pediatric respiratory system we measured the pressure drop across ETTs of 3 and 4mm inner diameter (ID) when we varied frequency, mean airway pressure and pressure amplitude of high-frequency-oscillation-ventilation (HFOV). Depending on ventilator settings the relative loss of mean pressure amplitude caused by the ETT ranged from 3.3% to 24.7% for ETT 4mm ID, respectively, from 23.8% to 51.8% for 3mm ID. In addition to the well-described flow dependency, ventilation frequency affected ETT resistance. Due to this frequency dependence, calculation of the pressure drop across the ETT using Rohrer's or Blasius-Itos' approach underestimated the true pressure drop significantly (p<0.001). Based on the experimental results, nomograms for graphical determination of the pressure drop across the ETT during HFOV were developed. We conclude that the pressure drop across the ETT during HFOV is dependent on ETT size, pressure amplitude and ventilation frequency. Calculation of this pressure drop with conventional methods is inaccurate. The high-frequency-resistance of the ETT might protect the lungs from excessive pressure amplitudes during HFOV.
在小儿呼吸系统的物理模型中，我们改变高频振荡通气（HFOV）的频率、平均气道压力和压力幅度，测量了内径（ID）为3mm和4mm的气管内导管（ETT）两端的压力降。根据呼吸机设置，内径4mm的ETT导致的平均压力幅度相对损失分别为3.3%至24.7%，内径3mm的ETT则为23.8%至51.8%。除了已充分描述的流量依赖性外，通气频率也会影响ETT阻力。由于这种频率依赖性，使用罗勒（Rohrer）或布拉修斯 - 伊托斯（Blasius-Itos）方法计算ETT两端的压力降会显著低估真实压力降（p<0.001）。基于实验结果，绘制了用于图形确定HFOV期间ETT两端压力降的列线图。我们得出结论，HFOV期间ETT两端的压力降取决于ETT尺寸、压力幅度和通气频率。用传统方法计算此压力降是不准确的。ETT的高频阻力可能会在HFOV期间保护肺部免受过高压力幅度的影响。
