MRCP-0922

A 68 year old man who has chronic obstructive pulmonary disease (COPD) is reviewed. On examination, there is evidence of cor pulmonale with a significant degree of pedal oedema. His FEV1 is 44%. During a recent hospital stay his pO2 on room air was 7.4 kPa. Which one of the following interventions is most likely to increase survival in this patient?