Arterial catheterization in small children is challenging, even for experienced anesthesiologists. For successful arterial catheterization, the arterial diameter, cross-sectional area, and depth from the skin surface are important considerations, especially in pediatric patients. THe investigators examined the posterior tibial artery (PTA) and dorsalis pedis artery (DPA) using ultrasound (US) to find a reasonable alternative arterial cannulation site to the radial artery (RA) in pediatric patients.

Inclusion Criteria:

• Patients undergoing general anesthesia needing invasive arterial monitoring

Exclusion Criteria:

• Surgery involving the both hands or foots