(196) Under Pressure: One Potential Danger of a Hidden Patent Foramen Ovale

Introduction: Patent foramen ovale (PFO) is a congenital heart defect in which the foramen ovale does not completely close after birth and remains patent in adulthood. Most PFOs are asymptomatic and incidentally discovered. Acute conditions causing elevated right atrial (RA) pressures, such as intubation or acute pulmonary emboli, may result in reversal of the typical pressure gradient, resulting in right-to-left shunting. This shunting results in blood flow bypassing the pulmonary circulation and subsequent significant hypoxemia may develop.

Description: A 55 year-old female with a past medical history of chronic diastolic heart failure, pulmonary hypertension (PH) diagnosed by transthoracic echocardiogram (TTE), and morbid obesity was scheduled for routine surgery. In the OR she was intubated and immediately became hypoxic with oxygen saturations falling to 60%. Increasing PEEP paradoxically worsened the degree of hypoxia. Intraoperative TEE revealed pathophysiology consistent with right-to-left shunting via a previously undiagnosed PFO. Emergent cardiology and pulmonology consultants recommended aborting the procedure and extubating in attempt to decrease intrathoracic pressure and decrease shunting. Upon extubation oxygenation improved, eventually returning to baseline. After discharge she underwent outpatient surgical PFO closure. Her baseline supplemental oxygen requirements have decreased since undergoing PFO closure.

Discussion: This patient had known PH with increased RA pressures as indicated on previous TTE. When she was mechanically ventilated during surgery, her right intracardiac pressures further increased resulting in right-to-left shunting via previously undiagnosed PFO. After extubation her intracardiac pressures returned to her physiologic baseline and oxygenation consequently improved.

This patient underwent TTE prior to operation as part of routine screening for PH. However, she had never had a bubble study performed. Had she undergone TTE with bubble study her PFO would have been revealed and further risk stratification and guidance would have been obtained. From this case we believe it would be advantageous for patients being screened for PH to undergo screening with bubble study to prevent unnecessary future complications, such as decompensation during mechanical ventilation.