Misleading Capnography in Acute Pulmonary Embolism: Case Series of Masked End-Tidal CO₂ Response During Airway...

End-tidal carbon dioxide (ETCO₂) monitoring is the standard method for confirming endotracheal tube placement during emergency airway management. However, massive pulmonary embolism can create paradoxical capnography findings that complicate airway confirmation and resuscitation efforts. We present two cases of cardiac arrest where massive pulmonary embolism masked expected ETCO₂ changes despite confirmed endotracheal tube placement. In the first case, a 33-year-old male with diabetic ketoacidosis developed cardiac arrest with absent colorimetric ETCO₂ change despite direct visualization of correct tube placement, leading to suspicion of massive pulmonary embolism. In the second case, a 68-year-old male who underwent below-knee amputation for necrotizing fasciitis experienced recurrent cardiac arrests with persistently low ETCO₂ values despite confirmed intubation and adequate ventilation. Both patients had massive pulmonary embolism confirmed on computed tomography pulmonary angiography and received thrombolytic therapy. These cases highlight that massive pulmonary embolism increases alveolar dead space, preventing carbon dioxide delivery to the alveoli and resulting in absent or persistently low ETCO₂ despite adequate ventilation. Clinicians should maintain high suspicion for pulmonary embolism when ETCO₂ remains paradoxically low despite confirmed endotracheal tube placement and adequate ventilation during cardiac arrest, particularly in patients with risk factors for venous thromboembolism.