Approval from Ethical Committee of Faculty of Medicine Universitas Indonesia was acquired prior conducting the study. Subjects were given informed consent before enrolling the study. Non-invasive blood pressure (NIBP) monitor, ECG and pulse-oximeter was set on the subjects in the operation room. The uncuffed endotracheal tube (ETT) diameter predictions were measured firstly using ultrasonography (USG), then with Cole formula. After that, polyvinyl chloride (Mallinckrodt) ETT intubation with Cole diameter measurement was inserted using direct laryngoscopy. If the ETT was too small, use a 0.5 mm bigger ETT than the prediction diameter, if it too big, use a 0.5 mm smaller ETT than the prediction diameter. Reintubation and measurements using both methods were recorded. If bradycardia or desaturation happened, positive pressure ventilation, 100% oxygen, atropine 0,01-0,02 mg/kg, adrenaline 0,01 mg/kg could be given. Data was analyzed using SPSS using Bivariat Chi-square test or Fisher Exact Test (categorical comparative analytical study).