A patient with suspected pulmonary embolism and ABG showing alkalemia (pH 7.50, PaCO2 29, PaO2 60, HCO3 20) should receive which intervention first?

• A. Prepare for mechanical ventilation
• B. Administer oxygen via facemask
• C. Prepare to administer a sedative
• D. Assess for indications of pulmonary embolism

Answer: (B)

When a patient with suspected pulmonary embolism has hypoxemia with respiratory alkalosis, the immediate priority is to improve oxygenation. The ABG shows alkalemia from low PaCO2 due to hyperventilation, and a markedly low PaO2 indicating insufficient oxygen delivery to the blood. Administering oxygen via a facemask directly addresses the hypoxemia, raises arterial oxygen tension, and stabilizes the patient while definitive diagnostic and therapeutic steps for the embolism are initiated.

Mechanical ventilation is not the first step unless there is impending respiratory failure or an inability to protect the airway. A sedative could depress respiration and worsen gas exchange in this setting. While evaluating for pulmonary embolism is essential, the most urgent action to improve outcome is correcting oxygenation with supplemental oxygen.