Nuclear medicine in ARDS: clinical applications

ARDS is still characterized by an exceedingly high mortality rate. Methods are then needed to detect ARDS at the earliest clinical stage. Over the last decade, radioisotopic techniques have developed, aimed at demonstrating an abnormal neutrophil sequestration in the lung or detecting functional alterations of the pulmonary alveolar-capillary barrier, which likely precede the onset of respiratory distress. Preliminary application of these techniques in patients with ARDS yielded conflicting results in terms of sensitivity and specificity. On the contrary, lung vascular abnormalities have been consistently observed in patients with ARDS studied by perfusion lung scanning. They consist of focal, non segmental perfusion defects, mostly peripheral and dorsal, with redistribution of blood flow to non-dependent lung regions. This scintigraphic pattern may be considered typical of ARDS since it is not observed in other acute lung disorders. Perfusion abnormalities on lung scans are detectable from the very early stage of ARDS and correlate with the severity of the syndrome as reflected by gas exchange, central hemodynamics, and chest radiography. Perfusion lung scanning may then be used in the early detection and evaluation of vascular injury in ARDS.