A 26-year-old woman with a history of asthma presents to the emergency department with increasing breathlessness and wheeze. She is unable to complete full sentences, respiratory rate is 30 breaths/min, pulse 118 beats/min, oxygen saturation is 90 percent on room air and peak expiratory flow is 30 percent of predicted. She has already used her Salbutamol inhaler repeatedly at home. What is the most appropriate immediate management step in the emergency department