A 32 year old woman with a history of asthma presents with worsening wheeze and shortness of breath despite using her salbutamol inhaler every 30 minutes. On examination, her respiratory rate is 32 breaths per minute, pulse 124 beats per minute, and peak expiratory flow is 35 percent of her best. She is able to speak in short phrases only and has widespread polyphonic wheeze. What is the most appropriate immediate management step?