The vanishing heart--deterioration on chest radiography with clinical improvement during prone position ventilation.

Prone position ventilation is used in the treatment of ARDS. Its beneficial effects are due to increased ventilation of the dorsal lung areas. Consequently, the now dependent parts of the lungs collapse, resulting in decreased sharpness of the cardiac silhouette. The latter may be misinterpreted as a worsening of the cardiopulmonary condition while, in fact, gas exchange and ventilation may be markedly improved. These features are illustrated in the case presented.