改进的面罩对无创人工通气死腔效应的影响

Modification of facial mask on the dead space effect in non-inasive mask ventilation

目的定量评价目前传统使用的面罩通气的重复呼吸量，探讨改进的双通道面罩对减少死腔效应的作用。方法选择７例慢性阻塞性肺疾病（ＣＯＰＤ）并轻中度二氧化碳（ＣＯ２）潴留患者，进行随机交叉自身对照试验。采用中号面罩，ＢｉＰＡＰ－３０呼吸机及平台型排气阀。应用电脑数据采集和分析方法，持续同步监测呼吸流量及ＣＯ２浓度，比较改进与传统面罩的重复呼吸量。结果改进面罩内呼气末ＣＯ２浓度明显低于传统法，分别为（３．０±１．０）％和（７．２±１．７）％（Ｐ＜０．００１）。传统面罩通气存在明显ＣＯ２重复呼吸，重复呼吸量为（８３．１±３２．９）ｍｌ；改进面罩通气几乎能完全消除重复呼吸［（０．１±０．４）ｍｌ，Ｐ＜０．０１］。结论传统面罩正压通气存在明显的ＣＯ２重复呼吸；改进面罩可基本消除 ＣＯ２重复呼吸，在治疗Ⅱ型呼吸衰竭患者时可能有重要的临床意义。

Objective There were reports concerning the CO2 rebreathing during non-invasive positive pressure ventilation (NIPPV) with full face mask. It is our hypothesis that modification of the mask from one way connection to two ways connection by making a side hole in the mask makes it possible that CO2 inside the mask could be washed out by a constant flow through the mask. Methods A randomized self-control study on CO2 rebreathing was conducted in 7 COPD patients to compare the modified set-up with the conventional one. A BiPAP- 30 ventilator and a plateau exhaustion valve (Respironics USA) were employed in the study. In the modified two ways set-up, the exhaustion valve (with distal end blocked) was connected to the side hole of the mask, so that a constant base flow could pass through the mask to the exhaustion valve. The average base flow was 0.43 LPS. The parameters were set as following: S/T mode, f: 15 BPM, pressure support level: 8 cm H2O. Three different levels of PEEP (2, 3 and 5 cm H2O) were used to investigate the PEEP level on CO2 rebreathing. Flow and CO2% were constantly recorded with computer data acquisition and analysis system (Microcal Origin). Results In conventional set-up, there was obvious CO2 rebreathing (rebreathing volume: 83.1 ± 32.9 ml). In modified connection, the rebreathing volume was only (0. 1 ± 0.4)ml (P<0.001). Conclusion There was obvious CO2 rebreathing during full face mask NIPPV in conventional set-up. A modified two ways connection could reduce CO2 rebreathing to be near zero, which might be important in the management of hypercapnic respiratory failure with NIPPV.