Patients were randomly divided into two groups: ultrasound-guided (US-guided) in-plane distal radial access (IP-DRA) and in-plane proximal radial access (IP-PRA) catheterization.

For IP-DRA , a linear transducer is placed in the radial fossa, which is known as the snuff-box. After obtaining a long-axis view of the radial artery ,the needle is inserted in the midpoint of the small footprint transducer. Then,the needle is advanced under real-time US guidance until visualizing the tip of the needle inside the artery .

For IP-PRA , a linear transducer is placed in the standard conventional forearm radial.

After obtaining a long-axis view of the radial artery ,the needle is inserted in the midpoint of the small footprint transducer. Then,the needle is advanced under real-time US guidance until visualizing the tip of the needle inside the artery .

*Ultrasound-guided catheterization of the radial artery, by proximal approach:

• Patient's hand in hyperextension with slight dorsiflexion of the wrist.
• The placement of the ultrasound probe initially linear in order to obtain the "short axis" image of the artery; then a quarter turn until obtaining a longitudinal "long axis" view.
• The operator must identify the artery using the pulsed wave Doppler;
• Insertion of the needle in the middle of the transducer providing an "in plane" orientation. Thus the needle was advanced slowly and its tip was visualized throughout the procedure. *Ultrasound-guided catheterization of the radial artery, by distal approach:
• If the right hand is along the body / if the left hand is on the trunk.
• The ultrasound probe placed at the level of the anatomical snuffbox by placing the transducer in a linear fashion then rotated coronally until a longitudinal image is obtained *In the 2 groups: - The longitudinal "in plane" approach is used - After visualization of the penetration of the bevel of the needle into the lumen of the artery and the jet of arterial blood into the syringe on aspiration, a flexible metal guide was introduced into the artery through the trocar according to the Seldinger's method. - The correct positioning of the guide in the artery was then confirmed by ultrasound. Any obstacle preventing insertion of the guide system always led to a new puncture.

Inclusion Criteria:

• Patients admitted in intensive care unit requiring a central venous catheter (CVC)

Exclusion Criteria:

• Patients with radial AV shunt for hemodialysis
• Patients with Renaud phenomenon or lymphedema
• Congenital or acquired deformity of arms
• Cannulation site infection, hematoma and surgery