Right-to-left interatrial shunt in ARDS: dramatic improvement in prone position

The mechanisms leading to shunting through a patent foramen ovale include h igh right-sided cardiac pressures and respiratory factors due to mechanical ventilation and also anatomical changes in the right atrium as described i n the platypnea-orthodeoxia syndrome. We report a patient with the adult re spiratory distress syndrome (ARDS) who had a right-to-left atrial shunt whi ch decreased in the prone position, after which oxygenation improved. The p atient was admitted to the intensive care unit because of ARDS due to an in vasive fungal infection. He had a history of chronic lymphocytic leukemia a nd paradoxical embolisms through a patent foramen ovale. Despite mechanical ventilation and antifungal treatment he developed severe ARDS. He was ther efore turned to the prone position. Blood gas values improved dramatically (arterial oxygen tension/fractional inspired oxygen ratio increasing from 5 9 to 278 torr). Transcranial Doppler sonography was performed with bubble s tudy, which confirmed a massive right-to-left shunt in the supine position and which instantaneously decreased in the prone position. This case sugges ts that a decrease in right-to-left shunt in patients who have a patent for amen ovale could partly explain the improvement in hypoxemia in the prone p osition.