Ultrasonographic measurements
Baseline measurements (T1) were performed before subcutaneous injection. All variables were measured again at 3 min after subcutaneous injection (T2) and immediately after radial artery cannulation (T3).The ultrasonic probe was placed longitudinally over the radial artery, and ultrasonographic measurements were recorded close to 2 cm from the radial styloid process. A mindray machine (M9, Shenzhen, Guangdong, China) with a 4–12 MHz variable frequency linear array transducer and a 1–5 MHz variable frequency convex array ultrasound transducer were applied. A set of vital signs and ultrasonographic parameters, such as internal diameter (cm, Fig. Ultrasonographic measurements: After activating pulsed wave Doppler ultrasound (PWD) mode, the volumetric gate was placed in the center of the arterial lumen, the arterial hemodynamics parameters were recorded. The ultrasound angle was kept between 30° and 60° in the process of the examination, which was defined as the angle between the direction of blood flow and the ultrasound beam. The time average maximal velocity (TAMAX, cm/s) was recorded as shown in Fig. 