At the end of the surgery, the study drugs are discontinued before the patient is extubated. If patients present clinical signs of residual neuromuscular blockade, they receive atropine 0.01mg/kg and neostigmine 0.04mg/kg. All patients receive dipyrone 30 mg/kg in bolus and a PCA device is connected to the intravenous line before discharge to the Post Anesthesia Care Unit (PACU). PCA solution containing morphine 1mg/ml in 0.9% saline, is set to give bolus of 2ml (2mg) with a 10min lockout interval.