Dexmedetomidine, a selective alpha2-adrenergic agonist is known to reduce propofol and opioid requirements due to its sedative and analgesic properties. However, until now, there has been studies based on indirect measures such as hemodynamics. Entropy shows to quantify the level of consciousness by EEG and Surgical pleth index(SPI) allows to predict the effect of pain stimuli and analgesic therapy by the index of the nociception-anti-nociception balance. The investigators analyzed quantitatively the requirements of propofol and remifentanil under continuous infusion of dexmedetomidine when using entropy and SPI.

Dexmedetomidine, a selective alpha2-adrenergic agonist is known to reduce propofol and opioid requirements due to its sedative and analgesic properties. However, until now, there has been studies based on indirect measures such as hemodynamics. Entropy shows to quantify the level of consciousness by EEG and Surgical pleth index(SPI) allows to predict the effect of pain stimuli and analgesic therapy by the index of the nociception-anti-nociception balance. The investigators analyzed quantitatively the requirements of propofol and remifentanil under continuous infusion of dexmedetomidine when using entropy and SPI.

Patients (20~65 years old, ASA class 1 or 2) scheduled lumbar discectomy under general anesthesia were recruited. The patients were randomly allocated to two groups. Both groups received Target controlled infusion(TCI) of propofol and remifentanil and the dexmedetomidine was added to the Dex group and normal saline was added to the Placebo group. The Dex group received 1mcg/kg loading dose followed by 0.5mcg/kg/hr infusion of dexmedetomidine which was administered at induction of anesthesia through skin closure. The placebo group received equal amount of normal saline. During maintenance of anesthesia the effect site concentration of propofol and remifentanil was titrated to maintain Entropy(SE) 40~60 and SPI under 50. Blood pressure and heart rate also was measured. The total amount of propofol and remifentanil administered, time between eye opening and extubation was recorded. The quality of recovery was evaluated by QoR-40 survey after 24 hours postop.

Inclusion Criteria:

1.The patients (20~65 years old, ASA class 1 or 2) scheduled lumbar discectomy under general anesthesia

Exclusion Criteria:

1. ASA class (American Society of Anesthesiologist physical status classification) 3 or higher
2. Patients with history of allergy or side effects on propofol, remifentanil, dexmedetomidine
3. BMI (body mass index) higher than 35
4. Patients taking monoamine oxidase inhibitor or adrenergic blocking agent
5. Pregnancy, Emergency operation
6. Patients with liver disease, cognitive dysfunction or drug abuse history