The records and scans of eight patients (three male; mean age, 30 years; range, 15 to 59 years) were examined (Table 1). Five patients presented after trauma sustained in road traffic accidents, one after an abdominal operation, one after cardiotho-racic surgery, and one patient after a severe pneumococcal pneumonia. At the time of entry into the study, each patient fulfilled the diagnostic criteria for ARDS used in our unit: an antecedent history of a precipitating condition, changes on chest radiograph suggestive of pulmonary edema, and a ratio of PaC>2:FI02 of <150 mm Hg (20 kPa) in the presence of normal plasma proteins and a pulmonary artery occlusion pressure <15 mm Hg.
All scans were performed on an electron beam ultrafast CT scanner (Imatron, San Francisco). Three-millimeter sections were performed at 10-mm intervals from the lung apices to bases in the supine position in all patients. Scan acquisition time was 200 ms and images were reconstructed using a high spatial resolution reconstruction algorithm. On the initial CT scan, ventilation was suspended at full inspiration asthma inhalers.
The CT images were viewed at window levels and widths appropriate for lung parenchyma (level, 500 HU; width, 900 to 1,500 HU). Immediately before each scan, a lung injury score (LIS), as described by Murray et al, was performed. The LIS is designed to provide a quantitative means of following the physiologic variables of patients with acute lung injury. In summary, lung compliance, the fractional inspired oxygen concentration, the degree of PEEP used, and a chest radiograph are scored numerically. A score greater than 2.5 is required before ARDS is diagnosed. A score of 0.1 to 2.5 is considered indicative of mild to moderate lung injury.
Table 1—Demographic Details of the Patients Studied
|Patient No.||Time to 1st CT,(d)||Time to 2nd CT,(d)||LIS (1)||LIS (2)|
|6 (abdominal operation)||12||134||1.0||0|