A 23-year-old woman presents to ED with acute shortness of breath and wheeze. She has a history of asthma, uses salbutamol as needed, and has had no admissions previously. On arrival: HR 118 bpm, RR 26, SpO2 94% on room air, speaking in full sentences. Chest auscultation reveals widespread wheeze. According to adult asthma guidance, what is the most appropriate initial pharmacological management in ED?