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呼吸机相关性肺炎:胸片与灌洗结果不一致
作者:佚名 来源:爱唯医学网   日期:2012-05-10 09:15
本文摘要:一项回顾性分析显示,临床医生常在无肺炎影像学证据的情况下对机械通气的创伤患者进行支气管肺泡灌洗(BAL)。在344例接受了BAL的患者的1.343份胸部X线片报告中,11%未发现浸润,64%无肺炎可疑。

    达拉斯(EGMN)——一项回顾性分析显示,临床医生常在无肺炎影像学证据的情况下对机械通气的创伤患者进行支气管肺泡灌洗(BAL)。在344例接受了BAL的患者的1.343份胸部X线片报告中,11%未发现浸润,64%无肺炎可疑(Med. Image Anal. 2012 [doi:10.1016/j.media.2012.02.005])。

    主要研究者、华盛顿大学的Heather L. Evans博士在外科感染学会(SIS)年会上表示:“我们的BAL适应证包括胸部X线片显示浸润或有改变,所以对于如此多BAL在不符合适应证的情况下实施,我感到很惊讶。我想这可能是因为一些医生担心患者不明原因出现分泌物增多、氧合增强以及脓毒症加重,而胸部X线片还不够令人信服。”  

    该研究涉及344例接受机械通气超过48 h的创伤患者,研究者对其在BAL前日、当日和次日的 1,343份胸部X线报告进行了文本分析。由2名经过专门培训的评审者根据临床肺部感染评分(CPIS)中的要素,将这些报告分为“无渗出”、“弥漫性渗出或肺不张”或“局灶性渗出”,并评为“无肺炎可疑”、“肺炎可疑”或“很可能为肺炎”。

    结果显示,CPIS分类的总准确率为90%,特异性和敏感性分别为93%和86%,阳性预测值为85%。“肺炎可疑”组的相应比例分别为85%、89%、78%和78%。

    正如预期,“局灶性渗出”在BAL阳性者中比在BAL阴性者中明显更多见(13% vs. 9%),“无渗出”则相反(11.5% vs. 15.3%)。然而,1,013份报告(75.4%)判断为“弥漫性渗出或肺不张”,并且50%给出了呼吸机相关性肺炎(VAP)的诊断。与BAL阴性者相比,BAL阳性者的影像学报告中明显更多提及“肺炎可疑”(28% vs. 45.6%),而“无肺炎可疑”则相反(68% vs. 60%)。

    在856份“无肺炎可疑”的胸部X线片报告中,430份(50%)来自BAL阳性患者。

    研究者根据时间对CPIS数据进行分层,发现BAL阳性组与阴性组之间在有无渗出方面的差异,仅在BAL次日的胸部X线片报告中存在显著性(P=0.004)。

    研究者表示,下一步工作将包括分析报告内容中的VAP风险评估数据。

    特邀评论员、范德比尔特大学的Addison K. May博士问道,研究者是否对胸部X线片报告与BAL结果仅40%吻合的发现感到意外,并询问研究者为何选择将BAL次日的影像学报告纳入分析。Evans博士回答称,上述发现并不意外,胸部X线片报告将会与其他临床指标一同被纳入VAP评估模型。 “将胸部X线片信息排除在外,等于是无视临床医生一直在使用的一部分基本数据。虽然我们不愿依赖胸部X线片,但几乎所有临床医生都承认这是诊断依据中的不可或缺的一部分。”至于第二个问题,Evans博士解释称,这样做是为了帮助训练分类者更加准确地作出判断,而且仅在BAL次日胸部X线片报告中存在统计学差异的结果令人意外和兴奋。

    实际上,美国疾病预防控制中心(CDC)已经从成人呼吸机相关性事件监测定义中撤掉了胸部X线片,这一新定义将从2013年开始实施。SIS前任主席Pamela Lipsett博士参与了新定义的修订工作,她反对在VAP诊断中使用胸部X线片,称该检查不可靠是其被排除的原因。

 

Chest X-Rays Incongruous With Lavage Results in VAP

BY PATRICE WENDLING
 

    DALLAS (EGMN) –Clinicians frequently perform bronchoalveolar lavage in ventilated trauma patients without radiologic evidence of pneumonia, according to a retrospective analysis.

    Among 1,343 chest x-ray reports from 344 patients who all underwent bronchoalveolar lavage (BAL), there was no mention of infiltrates in 11% and no suspicion of pneumonia in 64%, according to a review that used natural language processing to sift through the reports.

    “Our indication for BAL includes chest x-ray infiltrates or a change in chest x-rays, so I was very surprised to see that there were so many BALs done without an infiltrate mentioned in the chest x-ray report,” said lead author Dr. Heather L. Evans, a trauma and acute care surgeon and surgical intensivist at the University of Washington in Seattle. “I think that this may be something of a soft call when providers are concerned that the patient has increasing secretions, increasing oxygenation, and worsening sepsis of unknown etiology. Perhaps the chest x-ray is not as firm and fast a rule as we are led to believe.”

    Indeed, the U.S. Centers for Disease Control and Prevention removed the chest x-ray from its new surveillance definition for what is now termed adult ventilator-associated events. The new definition, expected to be implemented in 2013, is not intended for clinical management, leaving physicians in a quandary when making a clinical diagnosis of VAP. Enter natural language processing, a tool that is increasingly being applied in radiology as part of machine learning to aid in-text analysis of radiology reports (Med. Image Anal. 2012 [doi:10.1016/j.media.2012.02.005]).

    The investigators used natural language processing coding methods to code 1,343 chest x-ray reports from the day prior, day of, and day after BAL among 344 trauma patients ventilated for more than 48 hours at a level 1 trauma center. Two specially trained reviewers coded the reports using the chest x-ray element from the Clinical Pulmonary Infection Score (CPIS) as “no infiltrate,” “diffuse infiltrate or atelectasis,” or “focal infiltrate” and scored the reports on a three-point scale for suspicion of pneumonia as “no suspicion,” “suspicion,” or “probable pneumonia.”

    The CPIS classifier had a 90% overall accuracy, 93% specificity, 86% sensitivity, and 85% positive predictive value. The suspicion classifier achieved comparable results of 85%, 89%, 78%, and 78%, respectively.

    As expected, localized infiltrate was significantly more common in reports from BAL-positive than BAL-negative patients (13% vs. 9%), while no infiltrate was significantly more common in those from BAL-negative patients (15.3% vs. 11.5%). However, 1,013 chest x-ray reports, or 75.4% of the data, fell in-between with diffuse infiltrate or atelectasis and had a 50-50 chance of being diagnosed as VAP, Dr. Evans said at the annual meeting of the Surgical Infection Society.

    “Failure to discriminate diffuse infiltrate defines the group where culture data is most useful,” she observed.

    Radiology reports noting any suspicion of pneumonia were significantly more common in positive-BAL than in negative-BAL patients (45.6% vs. 28%), while reports with no suspicion of pneumonia were significantly more common in BAL-negative patients (68% vs. 60%).

    Still, 430 (50%) of the 856 chest x-ray reports with no suspicion of VAP were in patients with BAL-positive results, Dr. Evans pointed out.

    To sort out the implications of this finding, the investigators stratified the CPIS data by time and discovered that differences between the BAL-positive and -negative groups regarding the presence or absence of infiltrates were statistically significant only on chest x-ray reports from the day after BAL (P = .004).

    “Considering the timing of this chest x-ray report information is absolutely crucial and something we will definitely incorporate in the future,” she said, adding that future work will involve evaluation of coded chest x-ray report content in VAP risk assessment.

    Invited discussant Dr. Addison K. May, chief of trauma and surgical critical care at Vanderbilt University in Nashville, Tennessee, questioned whether the authors were surprised by the findings given that chest x-ray readings and BAL results correlate only about 40% of the time, and asked why the authors chose to include the radiology report from the day after BAL. Dr. Evans said the lack of correlation wasn’t surprising and that chest x-ray report language will be incorporated, along with other available clinical values, into their VAP risk assessment model.

    “To exclude the chest x-ray information is to ignore a fundamental piece of diagnostic data that clinicians use all the time,” she added. “As much as we don’t like to rely on the chest x-ray, I’m currently doing a qualitative study of the diagnosis of ventilator-associated pneumonia at my institution, and I can tell you in the 15 interviews I’ve done, every single person says the chest x-ray is a fundamental piece that they rely on to make the diagnosis.

    “So I think if we’re going to remove the chest x-ray from our definition, whether it’s from surveillance or from the definition that we use clinically, we have to have data to support that it shouldn’t be there.”

    Dr. Evans said the chest x-ray report from the day after BAL was included to help train the classifier to be accurate, and that the finding of statistical significance only for that day’s chest x-ray report data was unexpected and provocative.

    Dr. Pamela Lipsett, immediate past president of the Surgical Infection Society, was involved in the CDC’s redefinition of what is now termed ventilator-associated events. She argued against the use of chest x-rays for VAP diagnosis and said they were removed from the CDC definition because they are unreliable.

    Some attendees questioned why the authors didn’t just use a structured method for reading the radiographs. Dr. E. Patchen Dellinger, also a past president of the Society, simply asked, “Haven’t you just proved that we don’t know how to diagnosis VAP and that we should stop taking chest x-rays unless we’re worried about a pneumothorax?”

    Dr. Evans replied that there are many other indications for chest x-ray in the ICU, but added that “the days of getting a chest x-ray every morning just because the patient is ventilated are a gross overuse of that imaging modality.”

    The authors reported no relevant conflicts of interest.

(责任编辑:董明满)
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