A 70-year-old man with a history of COPD (FEV1 45% predicted), presents with a 2-day history of increased breathlessness, increased sputum volume which is now purulent, and increased wheeze. He is not pyrexial. His oxygen saturation is 90% on air. He normally uses tiotropium and a salmeterol/fluticasone combination inhaler. According to NICE NG114, what is the most appropriate initial management for this exacerbation in the community?