Objective : To determine the success of using medium-flow anesthesia with fresh gas flow (FGF) 2 Ipm in adults without gas and agent monitoring.Method : Three hundred and six patients (age 16-70 years, ASA physical status 1-2) undergoing surgery under general anesthesia with controlled ventilation were randomly allocated into 2 groups. Both groups receieved FGF 2 Ipm with standard monitoring (NIBP, ECG, Pulse oximeter) together with gas and agent analyzer. However, in the study group the anesthetists were unaware of gas and agent analyzer which were monitored by another anesthetist. Outcome measurement including SpO2, EtCO2, FiO2, isoflurane diual setting, Fi isoflurane, Fe isoflurane, heart rate, noninvasive blood pressure (NIBP), body temperature and urine output (if operative time was longer than 3 hours or excessive blood loss was predicted) were recorded. Failure of using this technique was defined as 1) SpO2<95% for 1 minute 2) EtCO2 > 45 mmHg for more than 3 minutes 3) FiO2 < 0.30 or 4) awareness > 0.2%. Results : There was no difference between the study and control groups regarding age, body weight, anesthetic technique, type of surgery, anesthesia time, operation time and medium-flow duration. The outcome measurement and the parameter in detecting failure of using medium-flow showed no difference. Conclusion : FGF 2 Ipm could be used successfully in adult patients neither using gas nor agent analyzer with lower cost than FGF 6 Ipm was used.