The aim of this study is to conduct a prospective, single-center randomized controlled study to investigate the effect of mild midazolam combined with sufentanil on radial artery cannulation in novice operators.

outcome: patients discomfort，visual analogue scale，First-attempt success rate，the success rate of radial artery cannulation within 10 minutes, Complication rate

Inclusion Criteria:

• Patients who required arterial cannulation for continuous blood pressure monitoring
• Aged >20years
• ASA physical status of 1-3
• BMI 18-28kg/m2
• All patients agreed to participate in this study at the time of recruitment and signed an informed consent form.

Exclusion Criteria:

• a positive Allen's test
• infection at the puncture site
• coagulation disorders; arterial diseases (such as Raynaud's disease or thromboangiitis obliterans)
• use of vasoactive drugs within 30 minutes before measurement during the study
• patients with arterial abnormalities and bends; hemorrhagic shock
• arterial atherosclerosis; radial artery puncture within the past 30 days
• chronic use of opioid or benzodiazepine drugs
• and known allergies or adverse reactions to benzodiazepines or opioids.