A 32-year-old male factory worker is brought to the emergency department 15 minutes after suspected inhalation of hydrogen cyanide gas during an industrial accident. He is conscious, anxious, with a respiratory rate of 28/min, heart rate 118/min, and blood pressure 142/88 mmHg. Arterial blood gas shows pH 7.28, PaCO₂ 32 mmHg, HCO₃⁻ 14 mEq/L, and normal PaO₂ on room air. What is the most appropriate immediate next step in management?