The propofol & half-fentanil ( Pf ) group , propofol & half-sufentanil ( Ps ) group and propofol & half-remifentanyl ( Pr ) group were given 0.5 g/kg fentanyl , 0.05 g/kg sufentanil and 0.5 g/kg remifentanyl , respectively and later administrated 1-2 mg/kg propofol .