The 50% effective concentration of remifentanil by target controlled infusion was not determined for inhibiting the haemodynamic response during double-lumen tube (DLT) intubation. Previous study showed that Airtraq videolaryngoscope provided more stable haemodynamics than Macintosh for double-lumen tube intubation. In this study, the investigators will compare the 50% effective concentration of remifentanil between Airtraq videolaryngoscope and Macintosh laryngoscope for inhibiting haemodynamic responses during DLT intubation.

Dixon "up-and-down" method was used to determine 50% effective concentration of remifentanil by target controlled infusion for inhibiting the haemodynamic responses during DLT intubation with Airtraq videolaryngoscope or Macintosh laryngoscope.

Inclusion Criterias:

1. American Society of Anesthesiologists physical status of I-II
2. Patients aged 18-65 years
3. BMI 18-35 kg/m2
4. Elective pulmonary surgery under general anesthesia to double-lumen tubes intubation
5. Mallampati classifications Ⅰ-Ⅱ

Exclusion Criterias:

1. Emergency operation
2. Anticipated difficult airway or history of intubation difficulties
3. Be allergic to any of the drugs used in the experiment, or have a history of drug allergy
4. Preoperative use of analgesic, sedative and other drugs
5. Uncontrolled hypertension and heart disease
6. Have a history of heavy smoking and alcohol abuse, serious drug abuse, and severe systemic infections
7. There are severe mental and nervous system symptoms, and patients cannot cooperate with the study, such as language comprehension disorder, mental illness, etc
8. Other clinical trials were conducted within 3 months prior to inclusion in the study