Enhancement of hypoxemia by right-to-left atrial shunting in severe asthma.

We report two cases of severe hypoxemia due to right-to-left shunt in acute asthmatic patients. During acute asthma, the transmural right atrial pressure can be higher than left atrial pressure during inspiration and then induce a right-to-left shunt through inter-atrial communication leading to hypoxemia. Contrast echography as well as Doppler analysis can easily confirm the diagnosis.