[Hypoxemia after heart surgery by a right-left shunt via a permeable unrecognized foramen ovale]

Hypoxemia is a relatively common complication in the immediate postoperative period after cardiac surgery under cardio-pulmonary bypass, usually due to pulmonary disease. When this does not improve with oxygen therapy and in the absence of pulmonary disease, it may be due to a right-to-left shunt. We report a case with a right-to-left intracardiac shunt due to persistence of a patent foramen ovale, which became functional again under the new hemodynamic conditions after surgery under cardiopulmonary bypass and assisted ventilation. The diagnosis and physiopathological mechanism were studied by cardiac catheterisation and angiography. Contrast echocardiography should be able to detect these acquired shunts relatively easily. The diagnosis requires appropriate therapy: discontinuation of ineffective assisted ventilation as this may aggravate the situation by increasing pulmonary resistance, and anticoagulant therapy to prevent potentially disastrous paradoxical thromboembolism.