A 19 year old man presents to the emergency department with dyspnea. He has a history of asthma, and has had 3 hospital admissions in the last year for asthma exacerbations. He has run out of his puffers for the past week. He is drowsy and unable to give a clear history. On exam, he is tachypneic at 35 breaths per minute, but otherwise using no accessory muscles. His HR is 130 beats per minute, with an O2 saturation of 88%. He is unable to use the peak flow meter. He has poor air entry on auscultation but no wheezing. What is the severity of his asthma exacerbation?