Received: 6 April 2018
Accepted: 1 April 2019
First Online: 9 April 2019
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board and Ethics Committee of Tohoku University School of Medicine (#2015-1-787, approved on March 17, 2016). We did not obtain informed consent from the study participants because we used opt-out sampling.
: Not applicable.
: All authors declare no competing interests regarding the publication of this study. This work was presented in part at the Annual Meeting of American Society of Anesthesiologists (ANESTHESIOLOGY 2016) on October 2016 in Chicago, IL, USA.
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