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?