A nurse is caring for a female client in the emergency department who reports shortness of breath and pain in the lung area. She states that she started taking birth control pills 3 weeks ago and that she smokes. Her heart rate is 110/min, respiratory rate 40/min, and blood pressure 140/80 mm Hg. Her arterial blood gases are pH 7.50. PaCO2, 29 mm Hg PaO2 60 mm Hg. HCO3 20 mEq/L and SaO2 86%. Which of the following is the priority nursing intervention?

Rationale: A. Administer oxygen via face mask is important because the client is hypoxic (SaO₂ 86%, PaO₂ 60 mm Hg), but this is not the highest priority. Oxygen supports tissue oxygenation but does not address the underlying life-threatening cause. B. Prepare for mechanical ventilation is incorrect because the client is currently alert and maintaining her airway. Mechanical ventilation is only needed if respiratory failure develops. C. Assess for indications of pulmonary embolism (PE) is correct because the client has multiple risk factors for PE: recent use of oral contraceptives, smoking, sudden onset shortness of breath, pleuritic chest pain, tachycardia, tachypnea, and hypoxemia. PE is life-threatening and requires immediate recognition and intervention to prevent complications such as shock or death. Nursing assessment and rapid diagnostic testing (e.g., CT pulmonary angiography, D-dimer) are essential first steps. D. Prepare to administer a sedative is incorrect because sedation could depress respiratory drive, worsening hypoxia in a patient with suspected PE. Sedatives are contraindicated in acute respiratory compromise unless specifically indicated for anxiety with careful monitoring.