A 72-year-old man with COPD presents with 3 days of increased dyspnoea, productive purulent sputum and wheeze. He has had two exacerbations in the past year. On examination, he is afebrile, SpO₂ 93% on room air, with widespread wheeze but no signs of pneumonia. What is the most appropriate initial management in addition to short-acting bronchodilators?