Korean J Anesthesiol when premedication is given with benzodiazepine or fentanyl, myoclonus is reduced by inhibition of subcortical neuronal activity [22,23]. In the case of this study, it was performed with a TCI pump to titrate the effect site concentration of remifentanil. In the absence of a TCI pump, a cautious bolus injection could be a substitution for the pump infusion. The effect site concentration of 4-6 ng/ml of remifentanil could be achieved by a bolus dose of 0.8-2.1 μg/kg if adjusted according for various ages and body weights [24]. The maximal time to the effect site concentration was about 70-100 seconds. Fifteen patients in Group Q ex- perienced chest wall rigidity. In Group R, the incidence of chest wall rigidity was significantly decreased and there was no other side effect. Opioid administration during induction has often been complicated by muscular rigidity and difficult ventilation. The sequelae of difficult ventilation are clinically important and can include hypertension, hypoxemia, pulmonary hypertension, respiratory acidosis, and increased intracranial pressure [25- 27]. Difficult or impossible ventilation after opioid induction is commonly ascribed to rigidity of the abdominal and thoracic musculature. There has been some evidence that fiber optic visualization of the glottis revealed closed vocal cords in some; however, they also described patients who had opened vocal cords but could not be ventilated [28]. The incidence of rigidity and severities varies depending on the kinds of opioid and doses used and the rate at which it is administered. To avoid serious airway obstruction like glottic closure, cautious dosing and administration must be carried out. In the case of our study, normal ranges of end tidal carbon dioxide showed there were no cases of airway obstruction. 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