Received: 18 August 2019
Accepted: 20 December 2019
First Online: 7 January 2020
: Not applicable as this is a review and meta-analysis. Trials meta-analysed have all received their original ethical approval.
: Not applicable.
: A/Prof. D. De Luca has received grants for research and educational projects from Chiesi Pharmaceuticals spa and ABBVIE inc. He also received travel grants from ABBVIE inc. He served as consultant and lecturer for both Chiesi Pharmaceuticals spa and ABBVIE inc. Finally, he was member of the advisory boards for both Chiesi Pharmaceuticals spa and ABBVIE inc. These companies produce two surfactants analyzed in the paper, but they had no role in design and conduct of the study; collection, management, analysis and interpretation of the data; preparation, review, approval of the manuscript or decision to submit it for publication.The other author declares no competing interests.