Arterial cannulation is a common invasive procedure performed in the emergency room, ICU and operating room indicated especially in major operation and critical patients to monitor beat to beat hemodynamic changes. Radial artery is most commonly used due to its superficial course, dual blood supply of the hand, and low risk of complications.

Radial artery cannulation was traditionally performed by palpation of radial artery pulsation. USG guided techniques have been widely used in various vascular cannulations because of its visual characteristics and higher success rate of cannulation compared with traditional palpation.

Dynamic needle tip positioning  is a new modified ultrasound technique that is shown to result in greater peripheral venous catheterization success rate when compared to long-axis in-plane view in a phantom model.Use of this method for radial arterial cannulation was described in a case report by Goh et al. The dynamic needle tip positioning method combines the advantages of short-axis out of plane and long-axis in-plane ultrasound techniques.

Very few studies have been done comparing this new modification of ultrasound technique with traditional palpation technique. Therefore, we propose to conduct this study and hypothesize that this new technique would result in significant increase in first pass success rate of radial artery cannulation.