Efficacy of the prognostic nutritional index (PNI) in critically ill COVID-19 patients: A multicenter study under a treatment regime in accordance with practice guidelines oleh Masayuki Kaku, Shoji Ando, Hiroshi Ono, Yurie Koga, Yuki Hotehama, Yusuke Enomoto, Masakazu Miyagi, Tatsuya Ito, Shota Araki, Shinichi Honjyo, Sachiko Atsuta, Nao Hino, Yoshiyuki Ito, Shigemi Kamiya, Satomi Inoue, Yuri Yotsumoto, Toshihiro Sakurai, Takeshi Nishikawa