BACKGROUND Intraoperative mechanical ventilation is a major component of general anesthesia. The extent to which various intraoperative tidal volumes and positive end-expiratory pressures (PEEP) effect on postoperative hypoxia and lung injury remains unclear. We hypothesized that adults having orthopedic surgery, ventilation using different tidal volumes and PEEP levels affect the oxygenation within first hour in the postoperative care unit. METHODS We conducted a two-by-two factorial crossover cluster trial at the Cleveland Clinic Main Campus. We enrolled patients having orthopedic surgery with general anesthesia who were assigned to factorial clusters with tidal volumes of 6 or 10 ml/kg of predicted body weight and to PEEP of 5 or 8 cm H2O in 1-week clusters. The primary outcome was the effect of tidal volume or PEEP on time-weighted average peripheral oxygen saturation measured by pulse oximetry divided by the fraction of inspired oxygen (Spo2/Fio2 ratio) during the initial postoperative hour. RESULTS We enrolled 2,860 patients who had general anesthesia for orthopedic surgery from September 2018 through October 2020. The interaction between tidal volume and PEEP was not significant (P = 0.565). The mean ± SD time-weighted average of Spo2/Fio2 ratio was 353 ± 47 and not different in patients assigned to high and low tidal volume (estimated effect, 3.5%; 97.5% CI, -0.4% to 7.3%; P = 0.042), for those assigned to high and low PEEP (estimated effect, -0.2%; 97.5% CI, -4.0% to 3.6%; P = 0.906). We did not find significant difference in ward Spo2/Fio2 ratio, pulmonary complications, and duration of hospitalization among patients assigned to various tidal volumes and PEEP levels. CONCLUSIONS Among adults having major orthopedic surgery, postoperative oxygenation is similar, with tidal volumes between 6 and 10 ml/kg and PEEP between 5 and 8 cm H2O. Our results suggest that any combination of tidal volumes between 6 and 10 ml/kg and PEEP between 5 versus 8 ml cm H2O can be used safely for orthopedic surgery. EDITOR’S PERSPECTIVE

中文翻译：

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全身麻醉期间的潮气量、呼气末正压和术后低氧血症：单中心多交叉因子集群试验。

背景技术术中机械通气是全身麻醉的主要组成部分。各种术中潮气量和呼气末正压（PEEP）对术后缺氧和肺损伤的影响程度仍不清楚。我们假设接受骨科手术的成年人、使用不同潮气量的通气和 PEEP 水平会影响术后护理室第一小时内的氧合。方法 我们在克利夫兰诊所主校区进行了二乘二因子交叉集群试验。我们招募了采用全身麻醉进行骨科手术的患者，他们被分配到阶乘组，潮气量为 6 或 10 ml/kg（预计体重），PEEP 为 5 或 8 cm H2O，每组 1 周。主要结果是潮气量或 PEEP 对术后最初一小时内通过脉搏血氧饱和度除以吸入氧分数（Spo2/Fio2 比率）测量的时间加权平均外周血氧饱和度的影响。结果我们招募了 2018 年 9 月至 2020 年 10 月期间接受全身麻醉进行骨科手术的 2,860 名患者。潮气量与 PEEP 之间的相互作用不显着（P = 0.565）。Spo2/Fio2 比率的平均值 ± SD 时间加权平均值为 353 ± 47，并且在分配为高潮气量和低潮气量的患者中没有差异（估计效果，3.5%；97.5% CI，-0.4% 至 7.3%；P = 0.042 ），对于分配为高和低 PEEP 的患者（估计效果，-0.2%；97.5% CI，-4.0% 至 3.6%；P = 0.906）。我们没有发现分配到不同潮气量和 PEEP 水平的患者在病房 Spo2/Fio2 比值、肺部并发症和住院时间方面存在显着差异。结论 在接受大型骨科手术的成人中，术后氧合相似，潮气量在 6 至 10 ml/kg 之间，PEEP 在 5 至 8 cm H2O 之间。我们的结果表明，6 至 10 ml/kg 之间的潮气量和 5 至 8 ml cm H2O 之间的 PEEP 的任何组合都可以安全地用于骨科手术。编辑的观点