Chest wall loading has been shown to paradoxically improve respiratory system compliance (CRS) in patients with moderate to severe acute respiratory distress syndrome (ARDS). The most likely, albeit unconfirmed, mechanism is relief of end-tidal overdistension in ‘baby lungs’ of low-capacity. The purpose of this study was to define how small changes of tidal volume (VT) and positive end-expiratory pressure (PEEP) affect CRS (and its associated airway pressures) in patients with ARDS who demonstrate a paradoxical response to chest wall loading. We hypothesized that small reductions of VT or PEEP would alleviate overdistension and favorably affect CRS and conversely, that small increases of VT or PEEP would worsen CRS. Prospective, multi-center physiologic study of seventeen patients with moderate to severe ARDS who demonstrated paradoxical responses to chest wall loading. All patients received mechanical ventilation in volume control mode and were passively ventilated. Airway pressures were measured before and after decreasing/increasing VT by 1 ml/kg predicted body weight and decreasing/increasing PEEP by 2.5 cmH2O. Decreasing either VT or PEEP improved CRS in all patients. Driving pressure (DP) decreased by a mean of 4.9 cmH2O (supine) and by 4.3 cmH2O (prone) after decreasing VT, and by a mean of 2.9 cmH2O (supine) and 2.2 cmH2O (prone) after decreasing PEEP. CRS increased by a mean of 3.1 ml/cmH2O (supine) and by 2.5 ml/cmH2O (prone) after decreasing VT. CRS increased by a mean of 5.2 ml/cmH2O (supine) and 3.6 ml/cmH2O (prone) after decreasing PEEP (P < 0.01 for all). Small increments of either VT or PEEP worsened CRS in the majority of patients. Patients with a paradoxical response to chest wall loading demonstrate uniform improvement in both DP and CRS following a reduction in either VT or PEEP, findings in keeping with prior evidence suggesting its presence is a sign of end-tidal overdistension. The presence of ‘paradox’ should prompt re-evaluation of modifiable determinants of end-tidal overdistension, including VT, PEEP, and body position.

中文翻译：

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对胸壁负荷的反常反应预示着对减少潮气量或 PEEP 的有利机械反应

胸壁负荷已被证明可以提高中度至重度急性呼吸窘迫综合征 (ARDS) 患者的呼吸系统顺应性 (CRS)。尽管未经证实，但最有可能的机制是缓解低容量“婴儿肺”的潮气末过度膨胀。本研究的目的是确定潮气量 (VT) 和呼气末正压 (PEEP) 的微小变化如何影响对胸壁负荷表现出反常反应的 ARDS 患者的 CRS（及其相关气道压力）。我们假设 VT 或 PEEP 的小幅降低会减轻过度扩张并有利地影响 CRS，相反，VT 或 PEEP 的小幅增加会恶化 CRS。预期，对 17 名中度至重度 ARDS 患者的多中心生理研究，这些患者表现出对胸壁负荷的反常反应。所有患者均在容量控制模式下接受机械通气并进行被动通气。在将 VT 减少/增加 1 ml/kg 预测体重和 PEEP 减少/增加 2.5 cmH2O 之前和之后测量气道压力。降低 VT 或 PEEP 可改善所有患者的 CRS。降低 VT 后，驱动压力 (DP) 平均下降 4.9 cmH2O（仰卧位）和 4.3 cmH2O（俯卧位），降低 PEEP 后平均下降 2.9 cmH2O（仰卧位）和 2.2 cmH2O（俯卧位）。在 VT 降低后，CRS 平均增加 3.1 ml/cmH2O（仰卧位）和 2.5 ml/cmH2O（俯卧位）。在降低 PEEP 后，CRS 平均增加 5.2 ml/cmH2O（仰卧位）和 3.6 ml/cmH2O（俯卧位）（P < 0. 01 全部）。大多数患者的 VT 或 PEEP 的小幅增加会使 CRS 恶化。对胸壁负荷有反常反应的患者在 VT 或 PEEP 降低后表现出 DP 和 CRS 的均匀改善，这一发现与先前的证据一致，表明其存在是潮气末过度扩张的迹象。“悖论”的存在应促使重新评估潮气末过度扩张的可变决定因素，包括 VT、PEEP 和体位。