Cooper David S, Schwartz Steven M, Raake Jenni L, Beam Abigail R, Nelson David P
Division of Cardiology, Cincinnati Children's Hospital, OH, USA.
Pediatr Crit Care Med. 2005 Mar;6(2):150-3. doi: 10.1097/01.PCC.0000154948.31058.6.
Supplemental inspired nitrogen (N(2)) or carbon dioxide (CO(2)) is commonly used to balance pulmonary blood flow in patients with single-ventricle physiology. The objective of this study was to assess if supplemental inspired gas alters delivery or measurement of tidal volume (V(T)) by a ventilator.
Prospective, experimental study.
Respiratory Care Laboratory, Cincinnati Children's Hospital.
Using a test lung, expired V(T) measurements from Servo 300 ventilators were compared with actual delivered V(T) (true V(T)) at baseline and during supplemental N(2) or CO(2) administration to mimic clinical use in single-ventricle patients. At compliance settings simulating normal and compromised lung function, true V(T) was determined by the test lung and inline Pneumotach. True and measured V(T) were compared by repeated-measures analysis of variance with significance defined as p < .05.
With normal lung compliance, supplemental gas administration increases both true and measured V(T), and expired V(T) measurements remain accurate. With poor lung compliance, supplemental gas flow disproportionately affects V(T) measurement. Poor lung compliance reduces true V(T) markedly (p < .001), causing a large discrepancy between true and measured V(T). Supplemental gas administration amplifies this discrepancy because the additional gas flow in the circuit erroneously augments expired V(T) measurements by the ventilator (p < .001). The discrepancy is greatest with higher-set V(T) and greater supplemental gas flow.
The addition of supplemental inspired gas directly into the ventilator circuit can alter tidal volume delivery or measurement by a ventilator. The extent and magnitude of the alterations are determined by lung compliance. Variable effects of supplemental gas administration may confound ventilator management of patients with single-ventricle physiology.
补充吸入氮气（N₂）或二氧化碳（CO₂）常用于平衡单心室生理患者的肺血流。本研究的目的是评估补充吸入气体是否会改变呼吸机潮气量（Vₜ）的输送或测量。
前瞻性实验研究。
辛辛那提儿童医院呼吸护理实验室。
使用测试肺，将Servo 300呼吸机的呼出Vₜ测量值与基线时以及补充N₂或CO₂期间实际输送的Vₜ（真实Vₜ）进行比较，以模拟单心室患者的临床使用情况。在模拟正常和受损肺功能的顺应性设置下，通过测试肺和在线呼吸流速仪确定真实Vₜ。通过重复测量方差分析比较真实Vₜ和测量的Vₜ，显著性定义为p < 0.05。
在肺顺应性正常时，补充气体给药会增加真实Vₜ和测量的Vₜ，呼出Vₜ测量值仍保持准确。在肺顺应性较差时，补充气体流量对Vₜ测量有不成比例的影响。肺顺应性差会显著降低真实Vₜ（p < 0.001），导致真实Vₜ与测量的Vₜ之间存在较大差异。补充气体给药会放大这种差异，因为回路中的额外气体流量会错误地增加呼吸机的呼出Vₜ测量值（p < 0.001）。在设置的Vₜ较高且补充气体流量较大时，差异最大。
直接向呼吸机回路中添加补充吸入气体会改变呼吸机的潮气量输送或测量。改变的程度和幅度由肺顺应性决定。补充气体给药的可变效应可能会混淆单心室生理患者的呼吸机管理。
