无创正压通气应用中呼气阀安装位置及类型对CO2重复呼吸影响的实验研究

Effect of location and type of exhalation valve on carbon dioxide rebreathing during noninvasive positive pressure ventilation：a experimental study

目的：研究无创正压通气（NPPV）应用中呼气阀安装位置及类型对CO2重复呼吸的影响。方法通过建立NPPV模型系统，将呼气阀分别安装于呼吸机管道和面罩之间（位置Ⅰ）以及面罩上（位置Ⅱ）。根据呼气阀安装位置及类型分为4组：A组为单孔型呼气阀安装于位置Ⅰ；B组为平台型呼气阀安装于位置Ⅰ；C组为单孔型呼气阀安装于位置Ⅱ，单孔型呼气阀远端封闭；D组为平台型呼气阀安装于位置Ⅱ，平台型呼气阀远端封闭。在标准化实验条件下，通过调节呼气气道正压（EPAP，分别设定为5 cmH2O和10 cmH2O，1 cmH2O＝0.098 kPa）、测试肺潮气量（VT，分别设定为300、400和500 mL），监测各组气管内或面罩内的呼气末二氧化碳分压（PETCO2）；单孔型呼气阀和平台型呼气阀分别安装于位置Ⅰ时，通过调节吸气气道正压（IPAP，分别设定为5、10、15、20 cmH2O），监测呼气阀的漏气量。结果①在标准化实验条件下，EPAP为5cmH2O时， A、B、C、D组气管内PETCO2（mmHg，1 mmHg＝0.133 kPa）分别为69.6±3.4、61.4±2.7、54.8±1.5、49.8±1.3，面罩内PETCO2分别为24.8±1.9、21.8±1.6、2.8±0.8、1.8±0.8；EPAP为10cmH2O时，A、B、C、D组气管内PETCO2分别为64.2±3.6、57.2±3.7、48.8±2.6、41.8±2.6，面罩内PETCO2分别为23.0±1.6、20.2±1.6、2.2±0.8、1.2±0.8。说明同种呼气阀安装在位置Ⅱ时气管内、面罩内的PETCO2明显低于安装在位置Ⅰ时（均P＜0.05）；而呼气阀安装在同一位置时，平台型呼气阀的PETCO2显著低于单孔型呼气阀（均P＜0.05）。②随着测试肺的VT升高，各组气管内PETCO2逐渐降低，VT 500 mL时的PETCO2（mmHg）显著低于VT300 mL和400 mL时（A组：51.4±2.7比72.8±2.9、69.6±3.4，B组：44.8±2.4比65.4±2.1、61.4±2.7，C组：36.8±1.9比59.0±1.6、54.8±1.5，D组：28.8±1.9比52.6±2.0、49.8±1.3，均P＜0.05）。③呼气阀安装在位置Ⅰ时，单孔型呼气阀的漏气量随测试呼吸机IPAP水平升高而增加，IPAP在5、10、15、20 cmH2O时，漏气量分别为（15.8±1.9）、（20.2±1.9）、（23.8±2.8）、（28.0±1.6） L/min；平台型呼气阀的漏气量则基本维持不变，分别为（24.2±1.6）、（23.8±1.6）、（25.2±1.6）、（25.2±1.6） L/min。结论呼气阀安装在面罩上比安装在呼吸机管道与面罩之间更有利于CO2的排出；同时，采用平台型呼气阀及适当增大肺VT也有利于排出CO2，从而减少CO2重复呼吸。

ObjectiveTo investigate the influence of exhalation valve location as well as its type on carbon dioxide （CO2） rebreathing during noninvasive positive pressure ventilation （NPPV）.Methods With a standardized NPPV experimental model system, the exhalation valve was respectively installed between the ventilator tube and mask （positionⅠ）, or on the mask （positionⅡ）. This study included four groups according to the position and type of exhalation valve, namely： single-arch exhalation valve was installed on the positionⅠ （A group）, and positionⅡ （C group, the distal end of single-arch exhalation valve was blocked）; plateau exhalation valve was installed on the positionⅠ （B group） and positionⅡ （D group, the distal end of plateau exhalation valve was blocked）. Under standard experimental condition, the pressure of end-tidal carbon dioxide （PETCO2） was monitored in the trachea or the mask through adjusting the expiratory positive airway pressure （EPAP, EPAP was set at 5 cmH2O and 10 cmH2O, 1 cmH2O = 0.098 kPa） and tidal volume （VT, VT was set at 300, 400, 500 mL）. Leakage of exhalation＆amp;nbsp;valve was monitored when single-arch exhalation and plateau exhalation valves were respectively placed in the positionⅠ through adjusting the inspiratory positive airway pressure （IPAP at 5, 10, 15, 20 cmH2O respectively）. Results① Under standard experimental condition, when EPAP was 5 cmH2O, PETCO2 （mmHg, 1 mmHg = 0.133 kPa） in the trachea was 69.6±3.4, 61.4±2.7, 54.8±1.5, 49.8±1.3 in A, B, C, D groups respectively; and it was 24.8±1.9, 21.8±1.6, 2.8±0.8, 1.8±0.8 in the mask, respectively. When EPAP was 10 cmH2O, the PETCO2 in the trachea was 64.2±3.6, 57.2±3.7, 48.8±2.6, 41.8±2.6 in A, B, C, and D groups respectively; and it was 23.0±1.6, 20.2±1.6, 2.2±0.8, 1.2±0.8 in the mask, respectively. For the same exhalation valve type, exhalation valve being installed on positionⅡ could induce significantly lower PETCO2 in the trachea and mask than that being installed on positionⅠ （allP〈 0.05）. For the same expiratory valve position, plateau exhalation valve produced significantly lower PETCO2 than single-arch valve （allP〈 0.05）.② As the VT increased, the PETCO2 in the trachea of each group was reduced obviously. When VT was 500 mL, PETCO2 （mmHg） was significantly lower than VT, which were 300 mL and 400 mL （A group： 51.4±2.7 vs. 72.8±2.9, 69.6±3.4; B group： 44.8±2.4 vs. 65.4±2.1, 61.4±2.7;C group： 36.8±1.9 vs. 59.0±1.6, 54.8±1.5; D group： 28.8±1.9 vs. 52.6±2.0, 49.8±1.3; allP〈 0.05）.③ When exhalation valve type was placed in positionⅠ, the air leakage of single-arch exhalation valve was increased to （15.8±1.9）, （20.2±1.9）, （23.8±2.8）, （28.0±1.6） L/min, and the plateau exhalation valve was essentially unchanged to （24.2±1.6）, （23.8±1.6）, （25.2±1.6）, （25.2±1.6） L/min as the IPAP was increased from 5, 10, 15, to 20 cmH2O. Conclusions Exhalation valve fixing on mask is more appropriate for CO2 discharge than that fixed on tube-mask valve. Plateau exhalation valve as well as moderately increasing VT is beneficial for CO2 discharge and CO2 rebreathing prevention.