Comparison between oxygen reserve index and end-tidal oxygen concentration for estimation of oxygenation during pre-oxygenation via a tight-fitted face mask: A prospective observational study. Issue 3 (March 2021) - Hirata, Naoyuki; Nishimura, Mitsuo; Chaki, Tomohiro; Yoshikawa, Yusuke; Yamakage, Michiaki