Desflurane is a halogenated ether with low solubility, giving rapid induction and emergence from anesthesia This character is suitable for Volatile Induction and Maintenance Anesthesia (VIMA). But desflurane can cause airway irritation when it used as a sole induction agent to adult or children, so there were many studies about reducing the airway reflex combined with desflurane.

Remifentanil is a short acting opioid and is quickly hydrolyzed by nonspecific esterase in the plasma and multiorgan. Several studies suggest the optimal dose of remifentanil for reducing airway reflex or cardiovascular response for intubation combined with desflurane. But these studies were under 1 Minimal Alveolar Concentration (MAC) of desflurane and this point could be a limitation because desflurane concentration over 1 MAC increase airway irritation significantly. This study this study was designed to determine a median effective effect-site concentration (EC50) of remifentanil to prevent airway irritation during desflurane anesthesia over 1 MAC.

Inclusion Criteria:

• patients for surgery requiring general anesthesia
• American Society of Anesthesiologists(ASA) classification I, II

Exclusion Criteria:

• history of gastroesophageal reflux, High grade obesity, Predicted difficult airway, Asthma, Chronic obstructive pulmonary disease(COPD), Upper respiratory infection (URI) within 3 weeks