- Following pre-oxygenation with 100% O2, anesthesia was induced with propofol and remifentanil, which were administered using a target effect-site concentration-controlled infusion pump (Perfusor® Space, B. Braun Melsungen, Germany) by using the models suggested by Schnider et al. and Minto et al (Minto et al., 1997; Schnider et al., 1998).