Propofol is widely used in general anesthesia induction, but the occurrence of peripheral intravenous pain is relatively high, causing anxiety, fear and other adverse emotions in patients , aggravating the stress response, and even leading to adverse events of cardiovascular system . The use of mediate-long chain fat emulsion propofol partly reduces the incidence of injection pain but patients can still suffer from different degrees of pain. Advanced intravenous injection of lidocaine can alleviate the pain of propofol injection, but its application method and dose are controversial. It is worthy of further discussion on how to select the appropriate dose of advanced intravenous injection of lidocaine to effectively prevent the injection pain of mediate-long chain fat emulsion propofol, and simultaneously avoid the adverse reactions of intravenous lidocaine, thus improving patient satisfaction and perioperative safety. In this study, in order to provide clinical references, sequential method was used to find the median effective dose (ED50) by means of pre-intravenous injection of lidocaine to suppress pain in mediate-long chain fat emulsion propofol injection.

Inclusion Criteria:

• Ages ranged from 18 to 65.
• ASA Ⅰ or Ⅱ level.

Exclusion Criteria:

• Allergy or contraindication to lidocaine or propofol; required for Central venipuncture catheterization;
• Abnormal liver or kidney function;
• Heavy drinking and long-term use of sedatives, analgesics or anti-anxiety drugs;
• Hearing and language impairment;
• Peripheral vascular disease;
• Severe cardiovascular disease or neurological disorders;
• Failure of one-time peripheral venipuncture;
• Infection of hand or wrist skin.