Department of Intensive Care Medicine, School of Medicine, University of Crete, Heraklion, Greece.
Department of Intensive Care Medicine, University Hospital of Heraklion, Heraklion, Crete, Greece.
Crit Care. 2020 Jul 28;24(1):467. doi: 10.1186/s13054-020-03169-x.
The driving pressure of the respiratory system is a valuable indicator of global lung stress during passive mechanical ventilation. Monitoring lung stress in assisted ventilation is indispensable, but achieving passive conditions in spontaneously breathing patients to measure driving pressure is challenging. The accuracy of the morphology of airway pressure (Paw) during end-inspiratory occlusion to assure passive conditions during pressure support ventilation has not been examined.
Retrospective analysis of end-inspiratory occlusions obtained from critically ill patients during pressure support ventilation. Flow, airway, esophageal, gastric, and transdiaphragmatic pressures were analyzed. The rise of gastric pressure during occlusion with a constant/decreasing transdiaphragmatic pressure was used to identify and quantify the expiratory muscle activity. The Paw during occlusion was classified in three patterns, based on the differences at three pre-defined points after occlusion (0.3, 1, and 2 s): a "passive-like" decrease followed by plateau, a pattern with "clear plateau," and an "irregular rise" pattern, which included all cases of late or continuous increase, with or without plateau.
Data from 40 patients and 227 occlusions were analyzed. Expiratory muscle activity during occlusion was identified in 79% of occlusions, and at all levels of assist. After classifying occlusions according to Paw pattern, expiratory muscle activity was identified in 52%, 67%, and 100% of cases of Paw of passive-like, clear plateau, or irregular rise pattern, respectively. The driving pressure was evaluated in the 133 occlusions having a passive-like or clear plateau pattern in Paw. An increase in gastric pressure was present in 46%, 62%, and 64% of cases at 0.3, 1, and 2 s, respectively, and it was greater than 2 cmHO, in 10%, 20%, and 15% of cases at 0.3, 1, and 2 s, respectively.
The pattern of Paw during an end-inspiratory occlusion in pressure support cannot assure the absence of expiratory muscle activity and accurate measurement of driving pressure. Yet, because driving pressure can only be overestimated due to expiratory muscle contraction, in everyday practice, a low driving pressure indicates an absence of global lung over-stretch. A measurement of high driving pressure should prompt further diagnostic workup, such as a measurement of esophageal pressure.
呼吸系统驱动压是被动机械通气期间整体肺应激的一个有价值的指标。在辅助通气中监测肺应激是不可或缺的，但要在自主呼吸的患者中实现被动条件以测量驱动压是具有挑战性的。在压力支持通气期间，在吸气末阻断时气道压力（Paw）的形态是否准确以确保被动条件尚未得到检验。
对压力支持通气期间危重症患者吸气末阻断获得的回顾性分析。分析流量、气道、食管、胃和膈下压力。当膈下压力恒定时/减小时，胃压的升高被用来识别和量化呼气肌活动。根据阻断后三个预定义点（0.3、1 和 2 秒）的差异，将阻断时的 Paw 分为三种模式：被动样下降后平台、“清晰平台”模式和“不规则上升”模式，后者包括所有延迟或持续增加的情况，无论是否存在平台。
共分析了 40 例患者和 227 次阻断。在 79%的阻断中识别出阻断时的呼气肌活动，并且在所有辅助水平都有。根据 Paw 模式对阻断进行分类后，在 Paw 呈被动样、清晰平台或不规则上升模式的情况下，分别有 52%、67%和 100%的病例识别出呼气肌活动。在 Paw 呈被动样或清晰平台模式的 133 次阻断中评估了驱动压。在 0.3、1 和 2 秒时，分别有 46%、62%和 64%的病例胃压升高，在 0.3、1 和 2 秒时，分别有 10%、20%和 15%的病例胃压升高超过 2cmH2O。
在压力支持通气中吸气末阻断时的 Paw 模式不能确保没有呼气肌活动和准确测量驱动压。然而，由于呼气肌收缩只能导致驱动压高估，因此在日常实践中，低驱动压表明整体肺过度拉伸不存在。高驱动压的测量应促使进一步的诊断工作，例如测量食管压力。
