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[JAMA作者回复]:心脏外科术后肺复张策略
2017年08月31日 研究点评, 进展交流 暂无评论

[编者按]:2017年4月8日,我们在网站上介绍了JAMA在线发表的RCT结果:肺保护性通气基础上肺复张对术后肺部并发症的影响。近日,JAMA刊登了两封读者来信,对该研究结果提出了自己的看法。

Comment & Response

August 15, 2017

Alveolar Recruitment Strategies After Cardiac Surgery—Reply

Marcelo B. P. Amato, Marcia S. Volpe, Ludhmila A. Hajjar

JAMA. 2017;318(7):668-669. doi:10.1001/jama.2017.8697

In Reply

Drs Li and Shi raised concerns about which of our study groups actually provided intensive alveolar recruitment. In Supplement 2, eFigure 4 and eTable 1 showed that the intensive maneuver resulted in better reversal of atelectasis (our main target). At arrival in the intensive care unit, electrical impedance tomography maps showed reduced ventilation and compliance of dependent lung regions for all patients (upper:lower ventilation ratio above 1:1), but a larger improvement occurred after the intensive maneuvers (upper:lower ventilation ratio decreased to 0.6 vs 1.2 in the moderate strategy group), leading to higher respiratory-system compliance (65 vs 50 mL/cm H2O) and better oxygenation (arterial partial pressure of oxygen [Pao2]/Fio2 ratio = 344 vs 236). The comparison between study groups was significant for all parameters.

Li医生和Shi医生对我们研究中两组患者究竟哪组接受了强化肺复张提出了质疑。在附录2中,eFigure 4与eTable 1显示,强化复张导致肺不张减少更多(我们的主要目的)。在进入ICU时,电阻抗CT显示所有患者重力依赖区域肺组织通气减少,顺应性降低(上肺与下肺通气比值超过1:1),但在强化复张后呈显著改善(上肺与下肺通气比值下降到0.6,而中等策略组为1.2),呼吸系统顺应性更高(65 vs 50 mL/cm H2O),氧合更好(Pao2/Fio2 比值 344 vs 236)。两组患者上述所有指标的比较均有显著差异。

The use of a lower Fio2 (40% in the intensive group vs 60% in the moderate group) was part of the intervention bundle decided a priori and based on pilot studies. The intention was to minimize hyperoxia,1eventually reducing reabsorption atelectasis.2 Ultimately, however, it resulted in higher arterial oxygenation in the intensive group (oxygen saturation, ≥97%, driven by better gas exchange in this group), which might have disadvantaged this strategy.1 A PEEP of 8 cm H2O was used in the moderate-strategy group because it was the standard of care at our institution. In contrast, the selection of a PEEP of 13 cm H2O for the intensive group was based on preliminary unpublished studies in which we performed decremental PEEP trials in a similar population of cardiac patients, with sequential measurements of lung collapse and hyperdistention.3 After studying 30 overweight patients, the median PEEP needed to avoid more than 5% of lung recollapse (after recruitment maneuvers) was 13 cm H2O. When we started the study, however, it was not practical to perform this monitoring during the trial, so we had to compromise with a fixed PEEP, knowing that it would be excessive for some but insufficient for others. We agree with Li and Shi that individualized PEEP might improve the results.

根据先导试验,我们事先确定采用较低的FiO2(强化组40%,中等组60%)作为集束化治疗的一部分。然而,这样的策略最终造成强化组动脉氧合更高(本组患者气体交换更佳,造成氧饱和度≥97%),这可能是这一策略的缺点。中等策略组使用PEEP 8 cmH2O,因为这是我们医院的常规治疗设置。与此相比,强化组选择13 cmH2O的PEEP,这是基于我们既往进行的未发表的研究结果。在那项研究中,我们对于相似的心脏外科患者采用了递减PEEP的方法,随后测定肺塌陷及过度牵张的情况。对于30名超重患者的分析显示,避免超过5%肺泡塌陷所需的PEEP中位数(肺复张后)为13 cmH2O。然而,当我们开始此项研究时,我们并不能常规进行此项监测,因此,我们做出了妥协,采用了固定的PEEP,尽管我们认识到,这一水平的PEEP对于某些患者而言可能过高,但对于其他患者可能不足。我们同意Li医生和Shi医生的观点,即个体化PEEP可能改善研究结果。

Drs Patel and Pfeifer are concerned that PEEP may have been harmful for hypoxemic patients. We suggest the opposite: hypoxemic patients have a higher probability of response to PEEP, as suggested by recent studies.4,5

Patel医生和Pfeifer医生就PEEP可能对低氧血症患者造成危害提出了疑虑。我们认为事实恰好相反:低氧血症患者更有可能对PEEP有反应,正如近期研究提示。

Regarding their concerns about power calculations, we argue that power calculations are typically based on the primary outcome, but this is not an absolute necessity, especially when a study is designed to have enough power for subgroup analyses or analysis of secondary outcomes. In our study, we aimed at guaranteeing a difference in outcomes that would convince clinicians. Thus, we used a dichotomized scale for power calculations, which is less powerful than a 5-degree ordinal scale comparison (as in our primary outcome), but that guaranteed a large enough sample size to show differences in grade 3 complications (implying clinically relevant complications). The lower-than-expected event rate in our control group (26% vs 30%), decreasing the chances of rejecting the null hypothesis, would only be a concern in case of a negative study. Fortunately, this was not the case.

至于他们对于样本量计算的质疑,我们认为,尽管样本量计算通常基于主要预后指标,但并不一定绝对如此,尤其当研究设计需要有足够的样本量进行亚组分析或对次要指标进行分析时。在我们的研究中,我们旨在确保有临床意义的预后指标存在差异。因此,我们采用了二分变量进行样本量计算,而非5级顺序变量比较(研究的主要预后指标),但要确保样本量足以发现3级并发症(即有临床意义的并发症)的差异。对照组事件发生率低于预期(26% vs 30%)尽管降低了拒绝零假设的概率,但仅在阴性研究结果时才会引发质疑。幸运的是,我们的研究结果并非如此。

References

1. Girardis  M, Busani  S, Damiani  E,  et al.  Effect of conservative vs conventional oxygen therapy on mortality among patients in an intensive care unit: the Oxygen-ICU randomized clinical trial.  JAMA. 2016;316(15):1583-1589.PubMedArticle

2. Rothen  HU, Sporre  B, Engberg  G, Wegenius  G, Reber  A, Hedenstierna  G.  Prevention of atelectasis during general anaesthesia.  Lancet. 1995;345(8962):1387-1391.PubMedArticle

3. Costa  EL, Borges  JB, Melo  A,  et al.  Bedside estimation of recruitable alveolar collapse and hyperdistension by electrical impedance tomography.  Intensive Care Med. 2009;35(6):1132-1137.PubMedArticle

4. Briel  M, Meade  M, Mercat  A,  et al.  Higher vs lower positive end-expiratory pressure in patients with acute lung injury and acute respiratory distress syndrome: systematic review and meta-analysis.  JAMA. 2010;303(9):865-873.PubMedArticle

5. Goligher  EC, Kavanagh  BP, Rubenfeld  GD,  et al.  Oxygenation response to positive end-expiratory pressure predicts mortality in acute respiratory distress syndrome: a secondary analysis of the LOVS and ExPress trials.  Am J Respir Crit Care Med. 2014;190(1):70-76.PubMedArticle

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