Concentration 2 - 3 ng/ml Dose of remifentanil according to the randomization: Letter U between 2 - 3 ng/ml. The infusions that were used to reach the (PC) target were: Group U = 2 - 3 ng/ml. 20 years old - 6.0 mcg/Kg/h, 30 years old - 5.7 mcg/Kg/h, 40 years old - 5.3 mcg/kg/h, 50 years old - 5.0 mcg/kg/h, 60 years old - 4.6 mcg/kg/h, 70 years old - 4.3 mcg/kg/h, 80 years old - 4.0 mcg kg/h.