A 55-year-old man with a known history of chronic obstructive pulmonary disease (COPD) presents to the emergency department with increased shortness of breath, wheeze, and a change in sputum colour to green over the past 3 days. His oxygen saturation is 89% on room air. He is alert and his respiratory rate is 26/min. According to NICE guidelines, what is the most appropriate initial management regarding antibiotics and corticosteroids?