Vieira S R, Puybasset L, Richecoeur J, Lu Q, Cluzel P, Gusman P B, Coriat P, Rouby J J
Unité de Réanimation Chirurgicale, Department of Anesthesiology and Department of Radiology (Thoracic Division), La Pitié-Salpêtrière Hospital, University of Paris VI, Paris, France.
Am J Respir Crit Care Med. 1998 Nov;158(5 Pt 1):1571-7. doi: 10.1164/ajrccm.158.5.9802101.
The aim of this study was to assess positive end-expiratory pressure (PEEP)-induced lung overdistension and alveolar recruitment in six patients with acute lung injury (ALI) using a computed tomographic (CT) scan method. Lung overdistension was first determined in six healthy volunteers in whom CT sections were obtained at FRC and at TLC with a positive airway pressure of 30 cm H2O. In patients, lung volumes were quantified by the analysis of the frequency distribution of CT numbers on the entire lung at zero end-expiratory pressure (ZEEP) and PEEP. In healthy volunteers at FRC, the distribution of the density histograms was monophasic with a peak at -791 +/- 12 Hounsfield units (HU). The lowest CT number observed was -912 HU. At TLC, lung volume increased by 79 +/- 35% and the peak CT number decreased to -886 +/- 26 HU. More than 70% of the increase in lung volume was located below -900 HU, suggesting that this value can be considered as the threshold separating normal aeration from overdistension. In patients with ALI, at ZEEP the distribution of density histograms was either monophasic (n = 3) or biphasic (n = 3). The mean CT number was -319 +/- 34 HU. At PEEP 13 +/- 3 cm H2O, lung volume increased by 47 +/- 19% whereas mean CT number decreased to -538 +/- 171 HU. PEEP induced a mean alveolar recruitment of 320 +/- 160 ml and a mean lung overdistension of 238 +/- 320 ml. In conclusion, overdistended lung parenchyma of healthy volunteers is characterized by a CT number below -900 HU. This threshold can be used in patients with ALI for differentiating PEEP-induced alveolar recruitment from lung overdistension.
本研究的目的是采用计算机断层扫描（CT）扫描方法评估6例急性肺损伤（ALI）患者呼气末正压（PEEP）诱导的肺过度膨胀和肺泡复张情况。首先在6名健康志愿者中确定肺过度膨胀情况，这些志愿者在功能残气量（FRC）和肺总量（TLC）时，气道正压为30 cm H₂O条件下进行CT扫描。在患者中，通过分析呼气末零压力（ZEEP）和PEEP时全肺CT值的频率分布来量化肺容积。在FRC时的健康志愿者中，密度直方图分布呈单相，峰值位于-791±12亨氏单位（HU）。观察到的最低CT值为-912 HU。在TLC时，肺容积增加79±35%，峰值CT值降至-886±26 HU。超过70%的肺容积增加位于-900 HU以下，表明该值可被视为区分正常通气与过度膨胀的阈值。在ALI患者中，在ZEEP时密度直方图分布要么是单相的（n = 3），要么是双相的（n = 3）。平均CT值为-319±34 HU。在13±3 cm H₂O的PEEP水平时，肺容积增加47±19%，而平均CT值降至-538±171 HU。PEEP诱导的平均肺泡复张为320±160 ml，平均肺过度膨胀为238±320 ml。总之，健康志愿者过度膨胀的肺实质特征是CT值低于-900 HU。该阈值可用于ALI患者，以区分PEEP诱导的肺泡复张与肺过度膨胀。
