All patients were treated in the ICU using modes of mechanical ventilation, an FIO2, and inotropic agents sufficient to produce an oxygen delivery index of 300 mL/min/m2 birth control.
The initial CT scan was performed as soon as the patient could be transferred safely to the CT scanning unit in a mechanically ventilated state. An LIS was performed immediately before the patient leaving the ICU for CT scanning. The scan was repeated as soon as possible after each patient was discharged from hospital and became fully ambulatory. A second LIS was performed on the same day as the CT scan using a standard chest radiograph and arterial gas analysis (Corning 170 blood gas analyzer, Corning UK, Essex).
Each CT image was assessed by two observers for the presence and distribution (the lung was divided into six zones: upper, middle, lower; anterior or posterior) of five patterns of disease as follows: (1) ground-glass opacification: hazy areas of increased attenuation of the lung parenchyma, without obscuration of the underlying vascular markings and bronchial walls; (2) consolidation: characterized by markedly increased attenuation of the lung parenchyma with obscuration of the underlying vascular markings usually accompanied by an air bronchogram; (3) reticular opacities: most frequently representing interlobular septa thickened by edema or fibrosis; (4) linear opacities: thickened interlobular septa or fibrous strands traversing areas of destroyed lung; and (5) parenchymal distortion: shown as distortion and dilatation of bronchi, so-called “traction bronchiectasis.”
The total extent of disease was derived by both observers visually estimating the percentage of abnormal lung to the nearest 5% at five predefined CT levels: (1) origin of the great vessels; (2) mid-arch of the aorta; (3) main carina; (4) pulmonary venous confluence; and (5) 1 cm above the right dome of diaphragm. Allowance was made for differences in lung volumes at these levels: the volume adjustment was made using a weighting factor, calculated from CT measurements of ten randomly selected patients with diffuse lung disease.