From the Departments of Anesthesia and Intensive Care (E.Ö., L.E.) Radiology (A.T.) the Center for Clinical Research (M.E.), Västerås Hospital, Västerås, Sweden the Department of Anesthesia and Intensive Care, Köping County Hospital, Köping, Sweden (E.Ö., L.E.) the Department of Surgical Sciences, Anesthesiology and Intensive Care (H.Z.) the Department of Medical Sciences and Clinical Physiology (G.H.), Uppsala University, Uppsala, Sweden.
Anesthesiology. 2019 Oct;131(4):809-817. doi: 10.1097/ALN.0000000000002764.
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.
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 30 min after extubation. Oxygenation was assessed by arterial blood gases.
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) cm and without PEEP 2.3 (-1.6 to 7.8) cm. The difference was 0.7 cm (95% CI, -0.8 to 2.9 cm; P = 0.400). Postoperative atelectasis for all patients was median 5.2 cm (95% CI, 4.3 to 5.7 cm), 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.
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.
呼气末正压通气（PEEP）可增加肺容积并防止麻醉期间肺泡塌陷。在苏醒期间，为拔管进行的安全预氧合会使肺容易吸收气体并发生肺泡塌陷，特别是在依赖 PEEP 保持开放的区域。我们假设在开始苏醒前预氧合之前撤去 PEEP 会限制术后肺不张的形成。
这是一项在 30 例健康患者中进行的随机对照评估者盲法试验，这些患者在全身麻醉和机械通气下接受非腹部手术，PEEP 为 7 或 9 cmH2O，具体取决于体重指数。手术结束时进行计算机断层扫描以评估基线时的肺不张。此后，将研究对象分为在苏醒前预氧合期间保持 PEEP（n = 16）或零 PEEP（n = 14）两组。主要结局是通过拔管后 30 分钟的第二次计算机断层扫描评估的肺不张面积变化。通过动脉血气评估氧合。
基线时的肺不张面积较小，在苏醒过程中适度增加，但两组之间无统计学差异。在苏醒期间应用 PEEP 时，肺不张面积的增加中位数（范围）为 1.6（-1.1 至 12.3）cm，而无 PEEP 时为 2.3（-1.6 至 7.8）cm。差异为 0.7 cm（95%CI，-0.8 至 2.9 cm；P = 0.400）。所有患者的术后肺不张中位数为 5.2 cm（95%CI，4.3 至 5.7 cm），相当于总肺面积的中位数 2.5%（95%CI，2.0 至 3.0%）。与术前清醒状态相比，两组患者的术后氧合均无变化。
在非腹部手术后苏醒前撤去 PEEP 不会减少术后肺不张的形成。尽管在苏醒期间使用 100%氧气，但术后肺不张面积较小，不会影响氧合，这可能取决于麻醉期间的开放肺，这是通过术中 PEEP 实现的。
