Paradoxical Hypoxemia Following Positive Pressure Ventilation: Exploring the Pathophysiology.

Unlabelled: Positive pressure ventilation (PPV), both non-invasive and invasive, enhances ventilation but can sometimes lead to unexpected hypoxemia. This case report describes an instance of paradoxical hypoxemia after initiating bilevel positive airway pressure (BiPAP) in a 58-year-old female with a medical history of systemic lupus erythematosus, interstitial lung disease, and pulmonary embolism. BiPAP was started, leading to improved hypercarbia but worsened hypoxemia. Further investigation revealed a right-to-left interatrial shunt via a small patent foramen ovale (PFO). Adjusting BiPAP settings improved arterial blood gas parameters. This case illustrates how positive pressure ventilation with underlying PFO can cause paradoxical hypoxemia. The case emphasizes the importance of understanding the pathophysiology and tailoring BiPAP settings based on individual haemodynamics.

Learning Points: Positive pressure ventilation can trigger paradoxical hypoxemia through a right-to-left shunt in patients with patent foramen ovale.Unexplained hypoxemia after initiating positive pressure ventilation warrants investigating intracardiac shunts with a saline contrast echocardiogram.Adjusting bilevel positive airway pressure settings based on individual haemodynamics is essential for improving oxygenation.