Received: 17 April 2018
Accepted: 18 July 2018
First Online: 31 July 2018
Ethics approval and consent to participate
: This study was approved by the Ethical Review Board, Faculty of Medicine, Kagawa University (Heisei 29-049). The consent form was acquired when anesthesia was explained or at the admission to the intensive care unit.
: The consent form was acquired at the time of the explanation of anesthesia or admission to the intensive care units.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.