A. Correct response: The evidence for the use of heliox in patients with COPD exacerbations is not robust or mature. Most of the peer-reviewed literature consists of case reports, case series, and physiologic studies in small samples of carefully selected patients. Even in the physiologic studies, a consistent response is not reported in all patients. Some patients with COPD exacerbations have a favorable physiologic response to heliox therapy, whereas others do not, and predicting who will be a responder and who will not is difficult.
B. Incorrect response: See explanation A.
C. Incorrect response: See explanation A.
D. Incorrect response: See explanation A.