Yanos J, Watling S M, Verhey J
Department of Medicine, Pulmonary/Critical Care Medicine, University of Missouri, Columbia, USA.
Chest. 1998 Sep;114(3):834-8. doi: 10.1378/chest.114.3.834.
The efficacy of inverse ratio ventilation in ARDS is not clear. Furthermore, the mechanism responsible has not been determined. We designed an animal study to determine if inverse ratio ventilation improves gas exchange and by what mechanism.
Prospective randomized, controlled design was used.
University of Missouri Pulmonary/Critical Care Animal Laboratory.
Nine dogs with oleic acid-induced lung injury as control animals to assess stability of the model, nine in the experimental model.
Conventional ventilation with full recruitment extrinsic positive end-expiratory pressure (PEEP) was compared with two other modes of ventilation. One was inverse ratio with extrinsic PEEP and the second was inverse ratio with intrinsic PEEP equal to full recruitment PEEP. Full recruitment levels of PEEP were defined by optimizing compliance, then increasing PEEP by 2.5 cm/H2O. Each type of ventilation was maintained for 45 min after the edema had stabilized. Comparison of lung injury over time requires stability of the model over time. Therefore, we also assessed the stability of the preparation over time by examining compliance, extravascular lung water, and venous admixture in nine control dogs with equivalent lung injury over the same time span.
Mean airway pressure was increased by both types of inverse ratio ventilation, while compliance remained stable. Venous admixture was reduced (conv=0.32+/-0.12, inverse ratio with extrinsic PEEP=0.24+/-0.10, inverse ratio with intrinsic PEEP=0.28+/-0.11) with inverse ratio with extrinsic PEEP, but the improvement was less with inverse ratio with intrinsic PEEP, even though the mean airway pressure was higher.
We conclude that increasing mean airway pressure by prolongation of the inspiratory time improves gas exchange in our model of ARDS, but when mean airway pressure is increased further, allowing the development of intrinsic PEEP, the beneficial effects on gas exchange are less. Increasing mean airway pressure with intrinsic PEEP is not equivalent to other methods of increasing mean airway pressure.
反比通气在急性呼吸窘迫综合征（ARDS）中的疗效尚不清楚。此外，其作用机制也未明确。我们设计了一项动物研究，以确定反比通气是否能改善气体交换及其作用机制。
采用前瞻性随机对照设计。
密苏里大学肺科/重症监护动物实验室。
9只油酸诱导肺损伤的犬作为对照动物以评估模型的稳定性，9只用于实验模型。
将采用完全复张性外部呼气末正压（PEEP）的传统通气与另外两种通气模式进行比较。一种是采用外部PEEP的反比通气，另一种是采用等于完全复张PEEP的内源性PEEP的反比通气。完全复张水平的PEEP通过优化顺应性来定义，然后将PEEP增加2.5 cm/H₂O。在水肿稳定后，每种通气类型维持45分钟。随着时间推移比较肺损伤需要模型随时间保持稳定。因此，我们还通过在相同时间段内检查9只具有等效肺损伤的对照犬的顺应性、血管外肺水和静脉血掺杂情况，评估了该制剂随时间的稳定性。
两种反比通气类型均使平均气道压升高，而顺应性保持稳定。采用外部PEEP的反比通气使静脉血掺杂减少（传统通气=0.32±0.12，采用外部PEEP的反比通气=0.24±0.10，采用内源性PEEP的反比通气=0.28±0.11），但采用内源性PEEP的反比通气改善程度较小，尽管其平均气道压更高。
我们得出结论，在我们的ARDS模型中，通过延长吸气时间增加平均气道压可改善气体交换，但当平均气道压进一步升高并导致内源性PEEP形成时，对气体交换的有益作用较小。采用内源性PEEP增加平均气道压与其他增加平均气道压的方法不等同。
