Lung CT Scan

In the last 20 years, the use of computed tomography (CT) to evaluate thoracic diseases has rapidly gained popularity and CT has become firmly established as an important research and diagnostic modality. In particular, CT has played an important role in improving our knowledge about the pathophysiology of the adult respiratory distress syndrome (ARDS) and in determining the morphological and functional relationships of different therapeutic options commonly used in the clinical management of this syndrome. CT scan may provide: 1) accurate measurement of the impact of mechanical ventilation on hyperaeration and reaeration/recruitment, being the most objective technique currently available to set mechanical ventilation and identifying patients for extracorporeal lung support; 2) the amount of lung edema, associated with the severity of the alveolar capillary barrier lesion and the risk of mortality; 3) clinical information in patients with a sudden and unexplained deterioration of the clinical status or the lack of expected improvement as well as to follow the evolution with time. We recommend to perform: 1) one single whole lung CT scan at end-expiration at PEEP 5 cmH2O, to evaluate the distribution of aeration and to compute the amount of lung weight; 2) only three lung CT slices, taken at the lung apex, hilum, and basis, at PEEP = 5 cmH2O and at Pplat = 45 cmH2O, to assess of lung recruitability; 3) a CT scan as early as possible after onset of ARDS (if clinical characteristics persist for more than 24 hours) and repeat it after 1 week if no clinical improvement is observed; 4) a CT scan in presence of any clinical deterioration not explained by conventional diagnostic tools. We suggest considering the measurement of extravascular lung water and end-expiratory lung volume by non radiological techniques and lung ultrasound if CT scan cannot be done.