Skimming J W, Cassin S, Blanch P B
Department of Physiology, University of Florida College of Medicine, Gainesville 32610, USA.
Chest. 1995 Oct;108(4):1065-72. doi: 10.1378/chest.108.4.1065.
Nitric oxide (NO) gas is known as both a vasodilator and a toxin. It can react with oxygen to form compounds more toxic than itself, such as nitrogen dioxide (NO2). The reactions are time dependent; thus, infusing NO into breathing circuits as close to ventilated subjects as possible may help minimize toxic byproduct exposure. Unfortunately, flow rates commonly used with mechanical ventilation favor laminar gas flow (streaming) within the breathing circuits. Streaming could delay mixing of NO with other inhaled gases. This mixing delay may interfere with accurate monitoring and/or delivery of NO. We tested the hypothesis that streaming of NO infused by constant flow into the inspiratory limb of a constant-flow mechanical ventilation system can lead to NO concentration delivery estimate errors. We then compared the NO2 concentrations at the ventilator Y-piece with three different NO mixing methods: blending the gases before they reach the breathing circuit inspiratory limb, infusing NO directly into the breathing circuit inspiratory limb far enough from the Y-piece to ensure thorough mixing, and infusing NO directly into the breathing circuit inspiratory limb immediately before the gases reach an in-line mixing device placed close to the Y-piece. Our results indicate that streaming can lead to NO concentration delivery estimate errors and that these errors can be characterized by measuring NO concentration variations across the inspiratory tubing's luminal diameter. NO2 concentration measured at the ventilator Y-piece were dependent on NO concentrations (p < 0.0001), NO delivery methods (p < 0.0001), and interactions between NO concentrations and NO delivery methods (p < 0.0001). We conclude that gas streaming and toxic byproduct exposure should be considered together when choosing an NO delivery method.
一氧化氮（NO）气体既是一种血管舒张剂，也是一种毒素。它能与氧气反应形成比自身毒性更强的化合物，如二氧化氮（NO₂）。这些反应具有时间依赖性；因此，尽可能在靠近通气受试者的呼吸回路中注入NO，可能有助于将有毒副产物的暴露降至最低。不幸的是，机械通气常用的流速有利于呼吸回路内的层流气体流动（气流）。气流可能会延迟NO与其他吸入气体的混合。这种混合延迟可能会干扰NO的准确监测和/或输送。我们测试了这样一个假设，即通过恒流注入恒流机械通气系统吸气支的NO气流会导致NO浓度输送估计误差。然后，我们比较了呼吸机Y形接头处采用三种不同NO混合方法时的NO₂浓度：在气体到达呼吸回路吸气支之前进行混合，将NO直接注入离Y形接头足够远的呼吸回路吸气支以确保充分混合，以及在气体到达靠近Y形接头的在线混合装置之前，将NO直接注入呼吸回路吸气支。我们的结果表明，气流会导致NO浓度输送估计误差，并且这些误差可以通过测量吸气管道内径上的NO浓度变化来表征。在呼吸机Y形接头处测得的NO₂浓度取决于NO浓度（p < 0.0001）、NO输送方法（p < 0.0001）以及NO浓度与NO输送方法之间的相互作用（p < 0.0001）。我们得出结论，在选择NO输送方法时，应同时考虑气体气流和有毒副产物暴露。
