Bugedo Guillermo, Retamal Jaime, Bruhn Alejandro
Departamento de Medicina Intensiva, Pontificia Universidad Catolica de Chile - Santiago, Chile.
Rev Bras Ter Intensiva. 2017 Apr-Jun;29(2):231-237. doi: 10.5935/0103-507X.20170032.
Overdistention and intratidal alveolar recruitment have been advocated as the main physical mechanisms responsible for ventilator-induced lung injury. Limiting tidal volume has a demonstrated survival benefit in patients with acute respiratory distress syndrome and is recognized as the cornerstone of protective ventilation. In contrast, the use of high positive end-expiratory pressure levels in clinical trials has yielded conflicting results and remains controversial. In the present review, we will discuss the benefits and limitations of the open lung approach and will discuss some recent experimental and clinical trials on the use of high versus low/moderate positive end-expiratory pressure levels. We will also distinguish dynamic (tidal volume) from static strain (positive end-expiratory pressure and mean airway pressure) and will discuss their roles in inducing ventilator-induced lung injury. High positive end-expiratory pressure strategies clearly decrease refractory hypoxemia in patients with acute respiratory distress syndrome, but they also increase static strain, which in turn may harm patients, especially those with lower levels of lung recruitability. In patients with severe respiratory failure, titrating positive end-expiratory pressure against the severity of hypoxemia, or providing it in a decremental fashion after a recruitment maneuver, is recommended. If high plateau, driving or mean airway pressures are observed, prone positioning or ultraprotective ventilation may be indicated to improve oxygenation without additional stress and strain in the lung.
肺过度扩张和潮气量内肺泡复张被认为是呼吸机所致肺损伤的主要物理机制。限制潮气量已被证明对急性呼吸窘迫综合征患者有生存益处，并被视为保护性通气的基石。相比之下，在临床试验中使用高呼气末正压水平产生了相互矛盾的结果，仍存在争议。在本综述中，我们将讨论肺开放策略的益处和局限性，并讨论一些关于使用高与低/中度呼气末正压水平的近期实验和临床试验。我们还将区分动态（潮气量）和静态应变（呼气末正压和平均气道压），并讨论它们在诱发呼吸机所致肺损伤中的作用。高呼气末正压策略明显可降低急性呼吸窘迫综合征患者的顽固性低氧血症，但也会增加静态应变，这反过来可能对患者造成伤害，尤其是那些肺复张能力较低的患者。对于严重呼吸衰竭患者，建议根据低氧血症的严重程度滴定呼气末正压，或在复张操作后以递减方式给予。如果观察到高平台压、驱动压或平均气道压，可能需要采用俯卧位或超保护性通气，以在不增加肺额外压力和应变的情况下改善氧合。
