A 25 year old patient with asthma arrives at the emergency depament complaining of extreme shoness of breath. He has been compliant with his medications, which are metaproterenol and inhaled betamethasone. Over the past 6 hours, his wheezing and shoness of breath have become increasingly severe. At present, his blood pressure is 136/84 mm Hg and with deep inspiration falls to 116/56 mm Hg. His pulse is 126/min, and respirations are 32/min and labored. There is retraction of the sternocleidomastoid muscles with inspiration. There are soft wheezes and poor air movement diffusely throughout both lung fields. His peak expiratory flow rate is 60 L/min, and he is immediately staed on an albuterol nebulizer and given IV hydrocoisone. His aerial blood gas revealed a pH of 7.55, pCO2 of 21 mm Hg, and a pO2 of 60 mm Hg. Twenty minutes later, a repeat peak flow rate is still 60 L/min. A repeat aerial blood gas reveals that his pH is now 7.46, his pCO2 is now 34 mm Hg, and his pO2 is 64 mm Hg. Which of the following is the most appropriate next step in management?