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Figure 5 | Critical Care

Figure 5

From: Measurement of alveolar derecruitment in patients with acute lung injury: computerized tomography versus pressure–volume curve

Figure 5

CT sections and P–V curves in a patient with diffuse loss of lung aeration. Image 1 shows a computed tomographic (CT) section representative of the whole lung obtained at zeron end-exoiratory pressure (ZEEP). The dashed line delineates the poorly aerated and nonaerated lung areas, which appear in light gray and red, respectively, on image 2 in accordance with a color-encoding system included in Lungview. Normally aerated lung areas are not observed and the delineation corresponds to the lung parenchyma present on the CT section. Image 3 shows the same CT section obtained at a positive end-expiratory pressure (PEEP) of 15 cmH2O. Image 4 shows the same CT section to which the color encoding has been applied, the normally aerated areas appearing in dark gray. In this patient without any normally aerated lung areas at ZEEP, alveolar derecruitment computed by the CT scan method is equal to the total decrease in functional residual capacity (ΔFRC = 583 ml). Because both CT and the pressure-volume (P–V curve) at ZEEP were acquired immediately after PEEP withdrawal, alveolar derecruitment is also equal to changes in end-expiratory lung volume measured by pneumotachography (596 ml). The P–V curve method markedly underestimates PEEP-induced alveolar derecruitment measured by the CT method.

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