When performing vascular cannulation such as radial artery cannulation, ultrasonography (US) helps proper positioning of the tip of needle in the vascular lumen, which facilitating cannulation of the catheter and successful pressure monitoring. Conventionally, short-axis out-of-plane (SAX) and long-axis in-plane (LAX) views are commonly used method to image the target vessel during cannulation under US guidance. Dynamic needle tip positioning (DNTP) method is newly introduced by one group of investigators who conducted a related study using vascular phantom model.

In DNTP, SAX is used, and additionally, when the needle tip is imaged in the screen as an echogenic point, the practitioner (a) proximally moves the US probe a bit, and then (b) the needle is advanced until the needle tip reappears in the screen. In this manner, the practitioner repeats (a) and (b) until the needle is inserted 1 cm into the lumen of vessel, and then the catheter is inserted to finish the procedure.

DNTP has not been compared to conventional imaging methods. The aim of this trial is to see the effect of DNTP on success rate of the radial artery cannulation at the first attempt, compared to the conventional LAX.

Inclusion Criteria:

• Elective cardiovascular surgery where RA catheterization is newly required.

Exclusion Criteria:

• skin infection or trauma
• Bilateral arteriovenous fistula for dialysis
• Severe peripheral vascular disease
• Severe arteriosclerosis or arterial atheroma
• Raynaud disease
• Shock
• Patients on ECMO or IABP support
• Morbid obesity
• Profound coagulopathy
• Negative results of modified Allen's test