A 57-year-old man presents with gradually worsening dyspnea on exertion for the past 6 months. He has a 40-pack-year history of tobacco use. He has noted a minimally productive cough, worse in the mornings, for the past 2 years. He is otherwise healthy, without hypertension, hyper-cholesterolemia, or diabetes mellitus. On physical examination, he is comfortable at rest. His room air oximeter reading is 93%. His neck veins are flat and his cardiac examination is normal. He has no basilar crackles, but breath sounds are distant bilaterally. Chest x-ray shows hyperexpansion without evidence of cardiomegaly or pulmonary congestion. What is the most important next step in staging this patient’s illness?A) Arterial blood gas
The Global initiative for chronic Obstructive Lung Disease (GOLD) guidelines recommend the use of spirometric values to standardize the diagnosis and staging of COPD. The diagnosis emphasizes a compatible history and evidence of fixed or incompletely reversible airway obstruction as demonstrated by a ratio of FEV1 to FVC less than 70%. Restrictive lung disease causes a proportional decline in both FEV1 and FVC; so the ratio of the two will remain normal. The stage of COPD is then determined by the decrease in FEV1 (see table). Table: Staging of COPD None of the other tests is recommended in the routine staging or management of COPD. Reliable finger oximeters have replaced ABGs as a means of checking for O2 desaturation. An elevated serum bicarbonate on a chemistry profile may indicate metabolic compensation for a chronic respiratory acidosis; sometimes (but not routinely) ABGs will be necessary to precisely quantify the degree of CO2 retention. Chest CT will demonstrate bullous changes in patients with emphysema but is not part of routine patient care. Patients with COPD will usually have limitation of exercise tolerance, but this can be estimated and followed by clinical history. Echocardiogram can confirm pulmonary hypertension (often indicative of cor pulmonale) in patients with clinical evidence of RV dysfunction but again is not necessary in the routine case. Giving O2 for relief of hypoxia is the best way of preventing mortality from cor pulmonale in these patients.