2.3 Ultrasound measurement
The patient lied in bed, the upper limbs were placed on both sides of the body, the back of the hand was perpendicular to the bed surface, and the left hand held the bandage. The sonographer palpated and marked the radial artery at the 2 cm proximal to the transverse crease of the wrist. The sonographer palpated and marked the distal radial artery at the anatomical snuffbox. The same sonographer used the same ultrasound machine and the same ultrasound probe to measure the distal radial artery and the radial artery of the left hand of all patients (Figure 1). The ultrasound machine was a PHILIPS CX50 (Royal Philips, Amsterdam, the Netherlands); the ultrasound probe was an L12-3 broadband linear array probe (probe frequency, 3-12 MHZ).