Abstract:

Background: Hypoxemia in postoperative Intensive Care Unit (ICU) patients is often multifactorial, with common causes including atelectasis, pneumonia, or pulmonary embolism. However, right-to-left shunting through a Patent Foramen Ovale (PFO) is a rare but critical diff erential diagnosis in
unexplained hypoxemia.

Case presentation: A 65-year-old male with a history of Chronic Obstructive Pulmonary Disease (COPD) was admitted to the ICU after colon cancer surgery. Preoperatively, he had no hypoxemia, but intraoperative hypoxemia developed and persisted postoperatively despite mechanical ventilation. Chest radiograph revealed mild bilateral lower lobe opacities. Given the suspicion of right-to-left shunting, a contrast echocardiography (Agitated Saline Contrast Echocardiography) was performed, which demonstrated a massive right-to-left shunt.