Comparison of the Effectiveness of Ultrasound-Guided Direct and Seldinger Cannulation Techniques in Patients With Anticipated Difficult Radial Artery Cannulation Undergoing Cardiac Surgery

Study Protocol and Patient Assessment: Data collection and the procedural intervention will be performed in the preoperative period, prior to the induction of anesthesia. All patients will undergo a modified Allen test. The radial artery site will be selected based on the following hierarchy: preferably the non-dominant hand (unless surgical plan dictates otherwise), an arm with no history of coronary angiography, and the side determined to be easiest for cannulation via ultrasound (USG) assessment.

Ultrasound Assessment and Exclusion: A 12 MHz linear ultrasound probe will be used for all assessments and procedures. Before the intervention, a detailed sonographic evaluation of the radial artery will be recorded, including:

• Artery diameter and wall thickness
• Lumen continuity and flow velocity
• Presence of calcification, vessel irregularity, or tortuosity
• Stenosis (percentage) and plaque characterization (stable/unstable; fibrous/fatty)
• Presence of hematoma, posterior wall injury, or dissection
• Skin- mid radial artery distance Patients with significant stenosis where an appropriate arterial segment matching the cannula diameter and length cannot be identified will be excluded from the study, and cannulation will be performed at an alternative site.

Randomization and Positioning: Patients will be randomized into two groups using a computer-generated random number table:

• Group D (Direct): Cannulation performed using the catheter-over-needle technique.
• Group S (Seldinger): Cannulation performed using the catheter-over-guide-wire technique.