2.1. Simulation training
Before starting the study, simulation training was conducted. The Intravenous ARM III (Kyoto Kagaku Co., Japan) simulator was used to train the direct visual and palpation techniques for peripheral venous access for 30 minutes. The peripheral venous catheter was BD Insight 22G, 25 mm (Nippon Becton Dickinson Co., Japan). A brief explanation of the principles of near-infrared venous imaging was given, and each participant searched for a vein in his or her own arm using near-infrared vein imaging. The near-infrared visualization system was Vein Viewer Flex (Terumo Co., Japan).Next, the principles of ultrasound guidance were briefly explained, followed by a demonstration of ultrasound imaging of veins in the upper extremities. Ultrasound imaging was performed with a Sonotore Linear (linear probe 7.5 MHz, ALFABIO Co., Japan). Out-of-plane (dynamic needle tip positioning