Received: 26 August 2019
Accepted: 9 January 2020
First Online: 3 February 2020
Ethics approval and consent to participate
: The study protocol was approved by the institutional review board (Ethics Committee of the Medical Faculty, University of Cologne, 17–407). Individual informed consent was waived due to the retrospective nature of the collected data.
: Not applicable.
: The authors declare, that they have no competing interests.