Devabhaktuni V G, Torres A, Wilson S, Yeh M P
University of Arkansas for Medical Sciences, Arkansas Children's Hospital, Little Rock, USA.
Crit Care Med. 1999 Aug;27(8):1603-7. doi: 10.1097/00003246-199908000-00037.
To determine the effect of heliox, nitric oxide (NO), and perfluorocarbon on differential pressure pneumotachometer characteristics and to determine the effect of heliox on volumes delivered by the Siemens S900C (S900C), and Servo Ventilator 300 (SV300) ventilators.
Prospective, laboratory study.
Pulmonary laboratory of a tertiary care, nonprofit children's hospital.
SV300, S900C ventilator, differential pressure pneumotachometer.
Dual pneumotachometers were connected in series to a 0.5-L calibration syringe and a 1-L anesthesia bag creating a closed system. Calibration of the pneumotachometers was done in room air at ambient temperature with 100 strokes. Accepted accuracy of measured volumes is within 0.5%. Flow-conductance curves were constructed using 100 strokes each for heliox (70:30 mixture), NO, and perfluorocarbon. Expired gases of room air and a 70:30 mixture of heliox from the above ventilators were collected into a nondiffusing gas collection bag, and the volume was measured in a chain-compensated gasometer. Ten sets of 500-mL breaths (20 breaths each set) and 100-mL breaths (40 breaths each set) were collected. The paired Student's t-test was used to detect significant differences in measured volumes, with significance defined as p < .01.
Volumes measured with the pneumotachometer using 25 ppm of NO, 50 ppm of NO, and perfluorocarbon were within +0.25%, -0.7%, and +0.4%, respectively (p = .155, p = .001, p = .06). Heliox decreased the conductance of the pneumotachometer, thereby increasing the measured volume by 15% (p < .001). However, heliox did not affect its linearity. Heliox had no affect on volumes delivered by the S900C. However, the SV300 delivered 7.9% less volume of heliox at a set tidal volume of 500 mL and 10.8% less at a set tidal volume of 100 mL.
A 70:30 mixture of heliox caused a significantly overestimated gas volume measured and, therefore, an underestimated gas volume delivered by SV300. NO at 25 ppm and perfluorocarbon did not interfere with the accuracy of a differential pressure pneumotachometer. However, at 50 ppm, NO caused a difference in measured gas volume that was statistically, but not clinically, significant. Application of pneumotachometers in critically ill children receiving heliox requires recalibration. Heliox did not affect volumes delivered with the S900C ventilator. Although volumes delivered with the SV300 were significantly reduced by heliox, the difference can be corrected easily by increasing minute ventilation until expired tidal volume equals desired tidal volume.
确定氦氧混合气、一氧化氮（NO）和全氟化碳对差压式呼吸流速计特性的影响，并确定氦氧混合气对西门子S900C（S900C）和Servo Ventilator 300（SV300）呼吸机输送气量的影响。
前瞻性实验室研究。
一家非营利性三级儿童医院的肺功能实验室。
SV300、S900C呼吸机及差压式呼吸流速计。
将两个呼吸流速计串联连接至一个0.5升校准注射器和一个1升麻醉袋，形成一个封闭系统。在室温环境空气中对呼吸流速计进行校准，共100次冲程。所测气量的可接受准确度在0.5%以内。分别使用氦氧混合气（70:30混合）、NO和全氟化碳各进行100次冲程来构建流量-传导曲线。将上述呼吸机的室内空气和70:30氦氧混合气体的呼出气体收集到一个非扩散性气体收集袋中，并在链式补偿气体量计中测量气量。收集10组500毫升呼吸（每组20次呼吸）和1组100毫升呼吸（每组40次呼吸）。采用配对t检验来检测所测气量的显著差异，显著性定义为p < 0.01。
使用25 ppm的NO、50 ppm的NO和全氟化碳时，呼吸流速计所测气量分别在+0.25%、-0.7%和+0.4%以内（p = 0.155、p = 0.001、p = 0.06）。氦氧混合气降低了呼吸流速计的传导性，从而使所测气量增加了15%（p < 0.001）。然而，氦氧混合气并未影响其线性度。氦氧混合气对S900C呼吸机输送的气量没有影响。然而，在设定潮气量为500毫升时，SV300输送的氦氧混合气量减少了7.9%，在设定潮气量为100毫升时减少了10.8%。
70:30的氦氧混合气体导致所测气体量显著高估，因此，SV300输送的气体量被低估。25 ppm的NO和全氟化碳不会干扰差压式呼吸流速计的准确性。然而，50 ppm的NO导致所测气体量存在统计学差异，但无临床意义。在接受氦氧混合气治疗的危重症儿童中应用呼吸流速计时需要重新校准。氦氧混合气不影响S900C呼吸机输送的气量。虽然氦氧混合气使SV300输送的气量显著减少，但通过增加分钟通气量直至呼出潮气量等于期望潮气量，该差异可轻松得到纠正。
