Miller Preston R, Meredith J Wayne, Chang Michael C
Department of Surgery, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA.
J Trauma. 2003 Aug;55(2):263-7; discussion 267-8. doi: 10.1097/01.TA.0000075786.19301.91.
BACKGROUND Identification of ventilator-associated pneumonia (VAP) with invasive methods such as bronchoalveolar lavage (BAL) paired with treatment is associated with improved mortality. Inappropriate antibiotic use, however, is known to increase bacterial resistance, making future treatment problematic. Thus, the diagnostic threshold for VAP in BAL must yield adequate sensitivity while limiting exposure of patients to unnecessary antibiotics. Our institution uses a cutoff of > or = 10(5) colony-forming units (CFUs)/mL, but the optimal cutoff remains an area of debate. In this project, the effects of lower diagnostic cutoffs on VAP diagnosis and unnecessary antibiotic use are examined.
Records of all patients admitted to the trauma intensive care unit over a 2-year period requiring > 48 hours of mechanical ventilation were reviewed. Number of BALs, quantity of organism on each BAL, and presence of VAP (> or = 10(5) CFUs/mL) were noted. Indication for BAL was pulmonary infiltrate, sepsis syndrome, and C-reactive protein > 17 microg/dL at > or = 48 hours after admission.
From January 1, 2000, to December 31, 2001, 563 patients were admitted to the trauma intensive care unit. Two hundred fifty-seven required > 48 hours of mechanical ventilation, and 257 BALs were performed in 168 (65%) of these patients. One hundred thirty-nine episodes of VAP occurred in 109 (42%) patients. Subdiagnostic quantities of bacteria (> or = 10(2) but < 10(5) CFUs/mL) were seen in 98 BALs. Of these, only 16 (16%) episodes of VAP with the same organism were seen later during hospitalization. At a threshold of > or = 10(4) CFUs/mL, 4 of 28 (14%) patients went on to develop pneumonia. A similar pattern was seen at diagnostic thresholds of > or = 10(3) CFUs/mL (10 of 72 [14%]) and > or = 10(2) CFUs/mL (16 of 98 [16%]).
A threshold of > or = 10(5) CFUs/mL for VAP diagnosis carries a low false-negative rate. Over 80% of additional patients who would have been treated had a threshold of > or = 10(4) CFUs/mL been used recovered without treatment and thus would have undergone unnecessary antibiotic exposure. A similar pattern is seen at all lower thresholds. Lower diagnostic thresholds would lead to marginal increase in sensitivity, and many would receive unnecessary VAP treatment with potential for increasing bacterial resistance.
背景 使用侵入性方法如支气管肺泡灌洗（BAL）并结合治疗来识别呼吸机相关性肺炎（VAP）与死亡率改善相关。然而，已知不恰当的抗生素使用会增加细菌耐药性，给未来治疗带来问题。因此，BAL中VAP的诊断阈值必须具有足够的敏感性，同时限制患者接触不必要的抗生素。我们机构使用的临界值为≥10⁵菌落形成单位（CFU）/mL，但最佳临界值仍是一个有争议的领域。在本项目中，研究了较低诊断临界值对VAP诊断和不必要抗生素使用的影响。
回顾了创伤重症监护病房2年内所有需要机械通气超过48小时的患者记录。记录BAL的次数、每次BAL中微生物的数量以及VAP（≥10⁵CFU/mL）的存在情况。BAL的指征为肺部浸润、脓毒症综合征以及入院后≥48小时时C反应蛋白>17μg/dL。
从2000年1月1日至2001年12月31日，563例患者入住创伤重症监护病房。257例需要机械通气超过48小时，其中168例（65%）患者进行了257次BAL。109例（42%）患者发生了139次VAP发作。在98次BAL中发现了亚诊断数量的细菌（≥10²但<10⁵CFU/mL）。其中，住院期间后期仅发现16例（16%）由相同微生物引起的VAP发作。在≥10⁴CFU/mL的临界值时，28例患者中有4例（14%）随后发生了肺炎。在≥10³CFU/mL（72例中的10例[14%]）和≥10²CFU/mL（98例中的16例[16%]）的诊断临界值时也观察到类似模式。
VAP诊断的临界值≥10⁵CFU/mL假阴性率较低。如果使用≥10⁴CFU/mL的临界值，超过80%原本会接受治疗的额外患者未经治疗就康复了，因此会遭受不必要的抗生素暴露。在所有较低临界值时都观察到类似模式。较低的诊断临界值只会使敏感性略有增加，许多患者会接受不必要的VAP治疗，有可能增加细菌耐药性。
