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[JAMA读者来信]:心脏外科术后肺复张策略
2017年08月24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

Guohui Li, Xueyin Shi

JAMA. 2017;318(7):667. doi:10.1001/jama.2017.8689

To the Editor

Dr Costa Leme and colleagues1 reported that an intensive alveolar recruitment strategy resulted in less-severe pulmonary complications than a moderate alveolar recruitment strategy among patients with hypoxemia after cardiac surgery. However, we have several concerns about the study.

Costa Leme医生及其同事报告,与中等程度肺复张策略相比,心脏外科术后低氧血症患者实施强化肺复张策略后肺部并发症较轻。然而,我们对此研究有一些疑虑。

The authors described 2 sustained inflation recruitment maneuvers. In the intensive strategy group, pressure-controlled ventilation plus positive end-expiratory pressure (PEEP) was performed under a driving pressure of 15 cm H2O with PEEP fixed at 30 cm H2O for 3 cycles (60 seconds each). In the moderate-strategy group, continuous positive airway pressure (CPAP) was used at a pressure of 30 cm H2O for 3 cycles (30 seconds each). However, it is difficult to identify which strategy was intensive or moderate according to the statements in the article. Were there any parameters such as levels of lung inflation or compliance to reflect the overall recruitment intensity of the 2 methods?

作者描述了2种持续充盈肺复张方法。在强化策略组,作者采用了压力控制通气及PEEP,维持驱动压15 cmH2O,PEEP固定为30 cmH2O,共3个周期(每个周期60秒钟)。在中等策略组,作者采用CPAP 30 cmH2O,共3个周期(每个周期30秒钟)。然而,根据文章的叙述,我们很难鉴别哪种策略是强化或中等。是否有相关指标如肺充盈或顺应性反映两种方法总体的复张强度?

In addition, the intensive recruitment strategy group had lower fraction of inspired oxygen (Fio2) than the moderate recruitment strategy group. Why were different levels of Fio2 used in the 2 groups?

另外,强化复张策略组FiO2低于中等复张策略组。两组患者FiO2为何存在差异?

For maintaining lung inflation, the intensive group kept PEEP at 13 cm H2O and the moderate group kept PEEP at 8 cm H2O after recruitment maneuvers. How were these PEEP values selected? Previous studies have demonstrated that the lower inflection point of the pressure-volume curve, the point of maximal compliance increase, dead-space fraction, tidal impedance variation by electrical impedance tomography, or PEEP:Fio2 tables could be used to set the optimal PEEP.2,3 The rationale for the PEEP settings in the 2 groups remains to be clarified.

为了维持肺的充盈,肺复张后强化组保持PEEP 13 cmH2O,而中等组维持PEEP 8 cmH2O。为何选择上述PEEP水平?既往研究显示,PV曲线低位转折点,顺应性增加最大的点,死腔通气,电阻抗CT测定的潮气量引起的阻抗变化,或PEEP:FiO2表格均可用于选择适宜的PEEP。两组患者PEEP设置的理由有待说明。

References

1. Costa Leme  A, Hajjar  LA, Volpe  MS,  et al.  Effect of intensive vs moderate alveolar recruitment strategies added to lung-protective ventilation on postoperative pulmonary complications: a randomized clinical trial.  JAMA. 2017;317(14):1422-1432.PubMedArticle

2. Suzumura  EA, Amato  MB, Cavalcanti  AB.  Understanding recruitment maneuvers.  Intensive Care Med. 2016;42(5):908-911.PubMedArticle

3. Hess  DR.  Recruitment maneuvers and PEEP titration.  Respir Care. 2015;60(11):1688-1704.PubMedArticle

Comment & Response

August 15, 2017

Alveolar Recruitment Strategies After Cardiac Surgery

Jayshil J. Patel, Kurt Pfeifer

JAMA. 2017;318(7):667-668. doi:10.1001/jama.2017.8693

To the Editor

The study by Dr Costa Leme and colleagues1 evaluated the effect of intensive (PEEP, 13 cm H2O) vs moderate (PEEP, 8 cm H2O) alveolar recruitment on reducing postoperative pulmonary complications in patients who had undergone cardiac surgery. The use of an intensive alveolar recruitment strategy compared with a moderate recruitment strategy resulted in less-severe postoperative pulmonary complications. We have some concerns about the research methods in this study.

Costa Leme医生及其同事的研究评价了强化(PEEP 13 cmH2O)与中等(PEEP 8 cmH2O)肺复张对心脏外科术后患者减少术后肺部并发症的作用。与中等复张策略相比,采用强化肺复张策略的患者术后肺部并发症较轻。我们对本研究的方法学有一些疑虑。

First, there seems to be discordance between the power calculation and primary outcome. The primary outcome (pulmonary complications severity score) was lower in the intensive strategy group than in the moderate strategy group. However, the study was not powered for the stated primary outcome. Rather, it was powered for a reduction in the incidence of major pulmonary complications, defined by grade 3 or higher on the postoperative pulmonary complications score.1

首先,样本量计算及主要预后指标不一致。强化策略组主要预后指标(肺部并发症严重程度评分)较中等策略组更低。然而,研究样本量并不足以验证这一主要预后指标的差异。事实上,样本量是根据主要肺部并发症(定义为术后肺部并发症评分3分或3分以上)发生率降低而计算的。

Second, the study may have been underpowered. In general, power calculations require 4 variables: significance level, power, baseline event rate (eg, outcome of interest in the control group), and the Δ (eg, outcome of interest in the control group minus the outcome of interest in the intervention group).2Power was 90% and significance was set at .05. The event rate for percentage of grade 3 or higher postoperative pulmonary complications in this study was estimated at 30% and the Δ was 15%.1 The actual Δ was 11%, suggesting overestimation of the rate of major complications. In fact, a trial of low-tidal volume ventilation during abdominal surgery to reduce postoperative pulmonary complications estimated the total event rate to be 20% whereas the actual rate was 27.5%.3

其次,研究样本量可能不足。通常情况下,样本量的计算需要4个指标:差异显著水平,把握度,事件的基线发生率(如对照组关注事件),以及差值(如对照组关注事件减去治疗组关注事件)。把握度90%,差异显著水平设置为0.05。本研究中,3级或以上术后肺部并发症的发生率估计为30%,差值为15%。真正的差值为11%,提示高估了主要并发症发生率。事实上,一项针对腹部手术期间实施小潮气量减少术后肺部并发症的研究中,估计事件总发生率为20%,而真正的发生率为27.5%。

Third, the trial included patients who were already hypoxemic. Intensive PEEP resulted in greater differences in both driving pressure and plateau pressure 15 minutes after the first and second recruitment maneuvers (eTable 1 in the article’s Supplement 2), suggesting the presence of lung injury. Furthermore, if lung injury was present (prior to the application of PEEP), how was it determined whether PEEP was harmful or beneficial? Before widespread application of intensive PEEP after cardiac surgery is applied, it would be prudent to identify which patients benefit from PEEP because some patients may be harmed.4

第三,研究入选患者已经为低氧血症。在第一次和第二次肺复张后15分钟,强化PEEP造成驱动压和平台压更大的差异(文章附录2中eTable 1),提示存在肺损伤。另外,如果存在肺损伤(在应用PEEP前),如何确定PEEP究竟有害抑或有益?在心脏外科术后广泛使用强化PEEP之前,应当谨慎鉴别哪些患者能够从PEEP中获益,因为PEEP对某些患者可能有害。

References

1. Costa Leme  A, Hajjar  LA, Volpe  MS,  et al.  Effect of intensive vs moderate alveolar recruitment strategies added to lung-protective ventilation on postoperative pulmonary complications: a randomized clinical trial.  JAMA. 2017;317(14):1422-1432.PubMedArticle

2. Summers  MJ, Chapple  LA, McClave  SA, Deane  AM.  Event-rate and delta inflation when evaluating mortality as a primary outcome from randomized controlled trials of nutritional interventions during critical illness: a systematic review.  Am J Clin Nutr. 2016;103(4):1083-1090.PubMedArticle

3. Futier  E, Constantin  JM, Paugam-Burtz  C,  et al; IMPROVE Study Group.  A trial of intraoperative low-tidal-volume ventilation in abdominal surgery.  N Engl J Med. 2013;369(5):428-437.PubMedArticle

4. Schmidt  GA.  Managing acute lung injury.  Clin Chest Med. 2016;37(4):647-658.PubMedArticle

 

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