De Jaegere A P, Jacobs F I, Laheij N G, van den Anker J N
Department of Pediatrics, Erasmus University, Rotterdam, The Netherlands.
Crit Care Med. 1997 Jun;25(6):995-1002. doi: 10.1097/00003246-199706000-00017.
To investigate the homogeneity of nitric oxide concentrations at different ventilator settings in a delivery system using a continuous flow ventilator.
A prospective bench study using a nitric oxide delivery system, mixing a nitrogen/nitric oxide gas mixture in the ventilator circuit with two types of continuous flow ventilators (Babylog 8000, Draeger, Luebeck, Germany; Infant Star, Infrasonics, San Diego, CA).
A biomedical laboratory.
A nitrogen/nitric oxide gas mixture was injected at three different sites in the ventilator circuit (just before and just behind the humidifier, and 20 cm before the Y-connector). Ventilator flow (12, 15, and 20 L/min) and rates (30 to 110 breaths/min with increments of 10 breaths/min) were changed as well as the compliance of the test lung (0.36, 0.5, and 1.0 mL/cm H2O). Carbon dioxide, instead of nitrogen/nitric oxide, was injected at the same points in the circuit.
The mean nitric oxide concentration increased significantly (p < .001) with increasing ventilator rates (although the flow ratio of the ventilator gas and the nitrogen/nitric oxide gas mixture was kept constant) when the nitrogen/nitric oxide injection site was near to the Y-connector of the ventilator circuit with both ventilators. The mean nitric oxide concentration did not change significantly when the nitrogen/nitric oxide gas mixture was mixed to the ventilator gas at the inlet of the humidifier, using the Babylog 8000 ventilator. Analysis of ventilator circuit flow patterns showed fluctuations during the respiratory cycle. The magnitude of the flow changes was different at the three injection sites in the ventilator circuit. Real-time measurements of the CO2 concentration showed fluctuations during the distinct respiratory phases that differed at the separate injection sites. Mean CO2 concentrations showed a similar pattern as compared with the mean nitric oxide concentration data at the same settings.
Mixing a nitrogen/nitric oxide gas mixture 20 cm before the Y-connector results in an increase of the mean nitric oxide concentration with increasing ventilator rates. This phenomenon does not occur with the nitrogen/nitric oxide gas mixture mixed at the inlet of the humidifier, using a ventilator with a throughout constant flow at the inspiratory outlet of the ventilator. The fluctuations of the main ventilator circuit flow result in changing ratios of nitrogen/nitric oxide gas mixture and the ventilator gas flow. We speculate this changing flow ratio produces the increase in mean nitric oxide concentration within the ventilatory circuit. To ensure a constant concentration of nitric oxide by blending a nitrogen/nitric oxide gas mixture in the ventilator circuit of a continuous flow ventilator, the site of injection of the nitrogen/nitric oxide gas mixture should be at the point where ventilator circuit flow fluctuations are minimal.
研究在使用连续气流呼吸机的输送系统中，不同呼吸机设置下一氧化氮浓度的均匀性。
一项前瞻性实验台研究，使用一氧化氮输送系统，将氮气/一氧化氮气体混合物在呼吸机回路中与两种连续气流呼吸机（德国吕贝克德尔格公司生产的Babylog 8000型；加利福尼亚州圣地亚哥英弗索尼克斯公司生产的Infant Star型）混合。
生物医学实验室。
在呼吸机回路中的三个不同位置（加湿器之前和之后，以及Y形接头前20厘米处）注入氮气/一氧化氮气体混合物。改变呼吸机流量（12、15和20升/分钟）、频率（30至110次/分钟，每次增加10次/分钟）以及测试肺的顺应性（0.36、0.5和1.0毫升/厘米水柱）。在回路中的相同位置注入二氧化碳而非氮气/一氧化氮。
当氮气/一氧化氮注入点靠近两种呼吸机的呼吸机回路的Y形接头时，随着呼吸机频率增加（尽管呼吸机气体与氮气/一氧化氮气体混合物的流量比保持恒定），一氧化氮平均浓度显著增加（p < 0.001）。使用Babylog 8000型呼吸机时，当氮气/一氧化氮气体混合物在加湿器入口处与呼吸机气体混合时，一氧化氮平均浓度无显著变化。呼吸机回路流量模式分析显示在呼吸周期中有波动。呼吸机回路中三个注入点的流量变化幅度不同。二氧化碳浓度的实时测量显示在不同呼吸阶段有波动，在不同注入点有所不同。与相同设置下的一氧化氮平均浓度数据相比，二氧化碳平均浓度呈现类似模式。
在Y形接头前20厘米处混合氮气/一氧化氮气体混合物会导致随着呼吸机频率增加一氧化氮平均浓度升高。当使用在呼吸机吸气出口处流量始终恒定的呼吸机，在加湿器入口处混合氮气/一氧化氮气体混合物时不会出现这种现象。主呼吸机回路流量的波动导致氮气/一氧化氮气体混合物与呼吸机气体流量的比例发生变化。我们推测这种变化的流量比例导致了通气回路中一氧化氮平均浓度的升高。为了通过在连续气流呼吸机的回路中混合氮气/一氧化氮气体混合物来确保一氧化氮浓度恒定，氮气/一氧化氮气体混合物的注入位置应在呼吸机回路流量波动最小的点。
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