Based on the fact that arterial vasodilation can be advantageous for endovascular catheterization and that an increase in body temperature can cause vasodilation by activating the cholinergic active vasodilator system, this study was planned to observe whether there was a significant change in the diameter of artery through ultrasound and to confirm the effectiveness of heating in the traditional palpation technique and the US-guided technique after local warming of the insertion site of arterial catheter in adult patients undergoing cardiac surgery.

Arterial cannulation is one of the important clinical techniques commonly used for real-time monitoring of blood pressure changes or when repeated blood tests are required. However, complications such as bleeding, hematoma, and vascular occlusion may occur if the operator has little or no experience in the procedure, or if arterial cannulation is not easy due to the patient's underlying disease and systemic factors. This situation prolongs the anesthesia induction time and may cause great harm to the patient in cases with a high bleeding tendency, such as in cardiac surgery. Various studies have reported various arterial cannulation techniques so far, and there have been many advances in arterial cannulation techniques due to the general use of ultrasound (hereafter US). However, there is still a risk of complications due to inexperience in the use of US or poor vascular status of the patient.

Inclusion Criteria:

• Adult patients over 18 years of age undergoing cardiac surgery under general anesthesia

Exclusion Criteria:

• If the patient already has an arterial catheter and does not need additional arterial cannulation.
• When arterial cannulation is performed on an artery other than the radial artery due to the surgical technique or the patient's condition.
• When the patient's condition is urgent, such as emergency surgery, and there is no time to proceed with the research.