Messinger G, Banner M J, Blanch P B, Layon A J
Department of Anesthesiology, University of Florida College of Medicine, Gainesville, USA.
Chest. 1995 Aug;108(2):509-14. doi: 10.1378/chest.108.2.509.
We evaluated the difference in work of breathing (WOB) during spontaneous ventilation with continuous positive airway pressure (CPAP) among three methods of triggering the ventilator: conventional pressure triggering, tracheal pressure triggering, and flow-by triggering.
In an in vitro model of the respiratory system consisting of a bellows (lungs) in a plastic canister (chest wall), spontaneous ventilation was simulated with a piston-driven pump (respiratory muscles). Data were recorded during CPAP of 5 cm H2O (model 7200ae ventilator, Puritan-Bennett, Overland Park, Kan) at peak sinusoidal inspiratory flow rate demands of 60 and 80 L/min and airway resistances of 5 and 20 cm H2O/L/s, with the demand flow system triggered by conventional pressure, tracheal pressure, or flow. Under each condition, tidal volume, pressure-time product (PTP), WOB, and changes in intrapleural pressure (Ppl) and airway pressure were recorded in real time by means of a computerized portable respiratory monitor (model CP-100, Bicore, Irvine, Calif). The Ppl was measured from within the canister, tidal volume by positioning a flow sensor between the Y-piece of the breathing circuit and the endotracheal tube (ETT), and airway pressure from a catheter attached to the flow sensor. The WOB was calculated by the monitor in real time.
Changes in Ppl were greatest with conventional pressure triggering, less with flow-by triggering, and least with tracheal pressure triggering. The WOB was significantly lower (approximately 50%) with tracheal pressure triggering than with the other two methods. With tracheal pressure triggering only, an effect similar to that of pressure support ventilation (PSV) occurred, which accounted in part for the significant decrease in WOB. The PTP/breath ratio correlated strongly and was a good predictor of WOB (r2 = 0.95).
Compared with conventional pressure and flow-by methods, triggering with tracheal pressure decreased WOB significantly. This method of triggering may improve patient-ventilator interaction.
我们评估了在持续气道正压通气（CPAP）下，三种触发呼吸机的方法（传统压力触发、气管压力触发和流速触发）在自主通气过程中呼吸功（WOB）的差异。
在一个体外呼吸系统模型中，该模型由塑料罐（胸壁）中的风箱（肺）组成，用活塞驱动泵（呼吸肌）模拟自主通气。在5 cm H₂O的CPAP（7200ae型呼吸机，普瑞美医疗，堪萨斯州欧弗兰帕克）期间，记录了峰值正弦吸气流量需求为60和80 L/min以及气道阻力为5和20 cm H₂O/L/s时的数据，需求流量系统由传统压力、气管压力或流速触发。在每种情况下，通过计算机便携式呼吸监测仪（CP - 100型，比科尔，加利福尼亚州欧文）实时记录潮气量、压力 - 时间乘积（PTP）、WOB以及胸膜腔内压（Ppl）和气道压力的变化。Ppl从罐内测量，潮气量通过在呼吸回路的Y形接头和气管内导管（ETT）之间放置流量传感器来定位，气道压力从连接到流量传感器的导管测量。WOB由监测仪实时计算。
Ppl的变化在传统压力触发时最大，流速触发时较小，气管压力触发时最小。气管压力触发时的WOB明显低于其他两种方法（约低50%）。仅在气管压力触发时，出现了类似于压力支持通气（PSV）的效果，这部分解释了WOB的显著降低。PTP/呼吸比相关性很强，是WOB的良好预测指标（r² = 0.95）。
与传统压力触发和流速触发方法相比，气管压力触发显著降低了WOB。这种触发方法可能改善患者 - 呼吸机的相互作用。
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