A client in a postpartum unit complains of sudden sharp chest pain and dyspnea. The nurse notes that the client is tachycardic and the respiratory rate is elevated. The nurse suspects a pulmonary embolism. Which of the following would be the initial nursing action?

A. Initiate an intravenous line: Establishing IV access is important for administering medications or fluids, but immediate oxygenation takes priority to prevent hypoxia and tissue damage in a suspected pulmonary embolism. B. Assess the client's blood pressure: Monitoring vital signs, including blood pressure, is essential for detecting hemodynamic instability, but it is secondary to ensuring adequate oxygenation in the acute phase of a pulmonary embolism. C. Prepare to administer Morphine sulfate: Morphine may relieve pain and anxiety, but it does not address the primary threat of hypoxemia or impaired oxygen delivery, making it a lower priority intervention. D. Administer oxygen at 8 to 10L/min by face mask: Supplemental oxygen helps maintain adequate oxygen saturation, reduces hypoxemia, and supports vital organ perfusion. In a client with sudden dyspnea and tachycardia suggestive of a pulmonary embolism, rapid oxygen delivery is the immediate priority.