A 65-year-old man with a 40 pack-year smoking history and known COPD presents with increased dyspnoea, more purulent sputum and a mild fever. His usual inhalers include a long-acting muscarinic antagonist (LAMA) and a long-acting beta2-agonist (LABA). Vitals: BP 130/80 mm Hg, HR 96 beats/min, RR 22 breaths/min, SpO2 90% on room air. Chest X-ray is unchanged. What is the most appropriate initial management for this COPD exacerbation?