A nurse in the emergency department is caring for a female client who reports shortness of breath and pain in the chest. The client states she began taking oral contraceptives 3 weeks ago and that she smokes. Her vital signs are: heart rate 110/min, respiratory rate 40/min, and blood pressure 140/80 mm Hg. Arterial blood gas results 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. The ABGs show respiratory alkalosis (pH 7.50, PaCO₂ 29) with hypoxemia (PaO₂ 60, SaO₂ 86%). The priority is to administer oxygen via face mask to correct hypoxemia. B. Mechanical ventilation may be needed if oxygen therapy is ineffective, but it is not the first action. C. A sedative is not appropriate because the hyperventilation is compensatory for impaired oxygenation. D. Assessing for pulmonary embolism is important (risk factors: oral contraceptives, smoking, sudden dyspnea), but ensuring oxygenation takes priority in the immediate situation.