Days after surgical fixation of a fractured femur, a client suddenly reports chest pain and difficulty in breathing. The nurse suspects that the client had a pulmonary embolus. Which action should the nurse take first?

A. While notifying the healthcare provider is important, the priority is to address the client's immediate physiological needs. B. Starting a continuous heparin infusion is important in the management of a pulmonary embolus, but providing oxygen is the first priority to ensure adequate oxygenation. C. Providing supplemental oxygen helps alleviate hypoxia, which is critical in the management of a pulmonary embolus. D. Bringing the emergency crash cart may be necessary if the client's condition deteriorates, but providing oxygen takes precedence in the initial management.