Review Question - QID 212383

A 66-year-old man presents to the emergency department due to a productive cough. His cough has been increasing in frequency and severity over the course of 3 days, and his sputum production has increased in volume. The color of his sputum is yellow-green. He denies any chest pain or palpitations but has experienced worsening shortness of breath with exertion and at rest, which is above his baseline. He has not noticed any changes in his weight or edema in his lower extremities. He denies any recent history of long travel. Medical history is significant for hypertension, hyperlipidemia, and chronic obstructive pulmonary disease (COPD). He has been hospitalized four times for similar symptoms within the last year. He has smoked approximately 1 pack of cigarettes per day for the past 45 years. His temperature is 102°F (38.9°C), blood pressure is 156/94 mmHg, pulse is 101/min, and respirations are 26/min with an oxygen saturation of 85% on room air. On physical exam, the patient has difficulty speaking, and there is asynchronous motion between the chest and abdomen with respiration. Wheezing is appreciated on pulmonary auscultation. An ECG demonstrates normal sinus rhythm. A chest radiograph is obtained, and he is administered supplemental oxygen. He is started on ipratropium, albuterol, and methylprednisolone. Which of the following should be added to this patient's treatment regimen?