Computed tomographic assessment of lung weights in trauma patients with early posttraumatic lung dysfunction

Abstract

Introduction: Quantitative computed tomography (qCT)-based assessment of total lung weight (Mlung) has the potential to differentiate atelectasis from consolidation and could thus provide valuable information for managing trauma patients fulfilling commonly used criteria for acute lung injury (ALI). We hypothesized that qCT would identify atelectasis as a frequent mimic of early posttraumatic ALI.

Methods: In this prospective observational study, Mlung was calculated by qCT in 78 mechanically ventilated trauma patients fulfilling the ALI criteria at admission. A reference interval for Mlung was derived from 74 trauma patients with morphologically and functionally normal lungs (reference). Results are given as medians with interquartile ranges.

Results: The ratio of arterial partial pressure of oxygen to the fraction of inspired oxygen was 560 (506 to 616) mmHg in reference patients and 169 (95 to 240) mmHg in ALI patients. The median reference Mlung value was 885 (771 to 973) g, and the reference interval for Mlung was 584 to 1164 g, which matched that of previous reports. Despite the significantly greater median Mlung value (1088 (862 to 1,342) g) in the ALI group, 46 (59%) ALI patients had Mlung values within the reference interval and thus most likely had atelectasis. In only 17 patients (22%), Mlung was increased to the range previously reported for ALI patients and compatible with lung consolidation. Statistically significant differences between atelectasis and consolidation patients were found for age, Lung Injury Score, Glasgow Coma Scale score, total lung volume, mass of the nonaerated lung compartment, ventilator-free days and intensive care unit-free days.

Conclusions: Atelectasis is a frequent cause of early posttraumatic lung dysfunction. Differentiation between atelectasis and consolidation from other causes of lung damage by using qCT may help to identify patients who could benefit from management strategies such as damage control surgery and lung-protective mechanical ventilation that focus on the prevention of pulmonary complications.

Figure 1

Flowchart illustrating group assignment. RIS/PACS, Radiology Information System and Picture Archiving and Communication Systems of the Department of Radiology. CT, computed tomography; PaO₂/FiO₂, ratio of arterial partial pressure of oxygen to fraction of inspired oxygen; reference spontaneous group, spontaneously breathing trauma patients with normal lung morphology on CT; reference ventilated group, mechanically ventilated trauma patients with normal lung morphology; ALI group, mechanically ventilated trauma patients fulfilling the criteria for acute lung injury (ALI) as defined by the American-European consensus conference (AECC) on acute respiratory distress syndrome [1]. Ø, exclusion criteria.

Figure 2

Comparison of lung weights. Lung weights of 78 patients with acute lung injury (ALI) upon admission (red circles) in comparison to the values of 43 mechanically ventilated trauma patients with morphologically and functionally normal lungs (reference ventilated, gray circles). Dashed lines mark the 95% reference intervals for total lung mass and total lung volume, respectively, calculated from reference ventilated patients. Because reference ventilated patients were ventilated with the same positive end-expiratory pressure (10 cmH₂O) and also underwent computed tomography during uninterrupted mechanical ventilation, only these reference ventilated patients were used for the graphical comparison with ALI patients in this graph. ALI patients whose data points fall within the gray box did not have an increased lung weight.