Received: 3 October 2019
Accepted: 6 April 2020
First Online: 11 May 2020
Ethics approval and consent to participate
: The study followed the principles of the Declaration of Helsinki and was approved by the Ethics Committee of Zibo Central Hospital. Written informed consents were obtained from the guardians of the patients.
: All authors have read and approved the manuscript for publication.
: The authors declare no competing interests.