In Doppler group decided to provide VE ( 10-30 m1/kg of Hydroxyethyl starches HES ) when the index stroke volume decreased by 15 % from the baseline value , in clinical group , hemodynamic variables triggering colloid administration mean arterial blood pressure ( MAP ) less than 20 % below baseline or central venous pressure ( CVP ) < 5 cmH2O in both groups : Ringer 's acetate was infused at constant rate ( 6 m 1/kg/h ) .