Limitations
The current study has some limitations. First, the total sample was relatively small. Second, subcutaneous nitroglycerin should be injected near the target site as the radial artery dilatation occurs locally near the injection site. Third, subcutaneous injection may mask the ultrasound image of the radial artery, so it should be carefully injected under direct ultrasound without bubbles. Fourth, we evaluated radial artery diameter and distal perfusion only intraoperatively. As the timing of catheter removal varies with the type of surgery and clinical situation, we were unable to assess the radial artery diameter and distal perfusion after catheter removal.