呼气末正压与术后肺不张：随机对照试验

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Positive End-expiratory Pressure and Postoperative Atelectasis : A Randomized Controlled Trial

背景与目的

呼气末正压(PEEP)可增加肺容量，防止麻醉过程的肺泡塌陷。在苏醒期间，拔管前安全的预充氧使肺容易受到气体吸收和肺泡塌陷的影响，特别是依赖于PEEP保持开放的区域。我们假设，在苏醒预充氧前撤除PEEP会减少术后肺不张的形成。

方  法

本项随机、对照、盲评试验，收集了在全身麻醉和机械通气下接受非腹部手术的30例患者，并根据体重指数将PEEP设置为7或9 cm H2O。手术结束时采用计算机断层扫描评估基础肺不张状态。随后，研究对象被分配接受苏醒预充氧期间维持一定压力PEEP(n=16)或零PEEP(n=14)。主要观察指标是肺不张面积的变化，拔管30分钟后进行第二次计算机断层扫描来对肺不张面积的变化进行评估。此外，用动脉血气测定氧合情况。

结 果  

基础状态肺不张面积较小，在苏醒期间轻度增加，两组间无统计学差异。在苏醒期间应用PEEP，肺不张面积增加的中位数（范围）为1.6（-1.1~12.3）cm2，而不使用PEEP的肺不张面积增加的中位数（范围）为2.3（-1.6~7.8）cm2。差异为0.7cm2（95%CI，-0.8~2.9cm2；P=0.400）。所有患者术后肺不张面积中位数为5.2cm2（95%CI，4.3~5.7cm2），相当于肺部总面积中位数的2.5%（95%CI，2.0~3.0%）。与术前清醒状态相比，两组患者术后氧合均无明显变化。

结 论

在苏醒预充氧前撤除PEEP并不能减少非腹部手术患者术后肺不张的形成。无论苏醒期间是否使用100%氧气，术后肺不张的发生率都很小，不影响氧合，这可能取决于麻醉期间肺部开放，如术中PEEP。

原始文献来源及摘要

Östberg E,  Thorisson A,  Enlund M,  et al. Positive End-expiratory Pressure and Postoperative Atelectasis: A Randomized Controlled Trial.[J] .Anesthesiology, 2019, 131: 809-817.

Abstract

Background: Positive end-expiratory pressure  (PEEP) increases lung volume and protects against alveolar collapse during anesthesia. During emergence, safety preoxygenation preparatory to extubation makes the lung susceptible to gas absorption and alveolar collapse, especially in dependent regions being kept open by PEEP. We hypothesized that withdrawing PEEP before starting emergence preoxygenation would limit postoperative atelectasis formation.

Methods: This was a randomized controlled evaluator-blinded trial in 30 healthy patients undergoing nonabdominal surgery under general anesthesia and mechanical ventilation with PEEP 7 or 9 cm H2O depending on body mass index. A computed tomography scan at the end of surgery assessed baseline atelectasis. The study subjects were thereafter allocated to either maintained PEEP (n = 16) or zero PEEP (n = 14) during emergence preoxygenation. The primary outcome was change in atelectasis area as evaluated by a second computed tomography scan 30min after extubation. Oxygenation was assessed by arterial blood gases.

Results: Baseline atelectasis was small and increased modestly during awakening, with no statistically significant difference between groups. With PEEP applied during awakening, the increase in atelectasis area was median (range) 1.6 (−1.1 to 12.3) cm2 and without PEEP 2.3 (−1.6 to 7.8) cm2 . The difference was 0.7 cm2 (95% CI, −0.8 to 2.9 cm2 ; P = 0.400). Postoperative atelectasis for all patients was median 5.2 cm2 (95% CI, 4.3 to 5.7 cm2 ), corresponding to median 2.5% of the total lung area (95% CI, 2.0 to 3.0%). Postoperative oxygenation was unchanged in both groups when compared to oxygenation in the preoperative awake state.

Conclusions: Withdrawing PEEP before emergence preoxygenation does not reduce atelectasis formation after nonabdominal surgery. Despite using 100% oxygen during awakening, postoperative atelectasis is small and does not affect oxygenation, possibly conditional on an open lung during anesthesia, as achieved by intraoperative PEEP.

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