Brief H&P:

A 67 year-old male with a history of hypertension and diabetes presents to the emergency department after a syncopal episode. He had been completing his normal morning routine when he developed a sensation of lightheadedness and awoke on the ground of his kitchen. He denies associated chest pain, palpitations, diaphoresis, or recent illness. He has no known sick contacts nor exposures to individuals undergoing evaluation for COVID-19.

On arrival in the emergency department, the patient was noted to be hypoxic with pulse oximetry measuring 74%. He was placed on supplemental oxygen via non-rebreather with improvement of oxygen saturation to 94%. Examination demonstrated diminished alertness (requiring constant stimulation for responses) and generalized motor weakness. Cardiac and pulmonary examinations were unremarkable with the exception of tachypnea and no extremity edema was appreciated.

A chest radiograph was obtained which demonstrated platelike atelectasis. An arterial blood gas was obtained with PaO2 of 72mmHg suggesting a prominent A-a gradient. CT pulmonary angiography was obtained:


CT Pulmonary Angiography:

Bilateral pulmonary emboli. Case courtesy of Associate Prof Frank Gaillard, Radiopaedia.org, rID: 19636

Upon return, the patient’s mental status worsened associated with hypotension and he was intubated for airway protection and received systemic thrombolysis. He was subsequently taken for emergent endovascular treatment of massive pulmonary embolus.

An Algorithm for the Differential Diagnosis of Hypoxemia & Hypoxia1-7

Hypoxemia is defined as low PaO2 while hypoxia is insufficient global or local tissue oxygen content.

An Algorithm for the Differential Diagnosis of Hypoxemia and Hypoxia


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