The goal of this observational study is to understand the incidence and risk factors of complications associated with midline catheter placement in pediatric patients (under 18 years old) undergoing general anesthesia. The main questions it aims to answer are:

What is the overall complication rate (including malfunction, bleeding, thrombosis, inflammation, and infection) after midline catheter placement in children?

What factors (e.g., age, weight, vein diameter, insertion site, catheter maintenance duration) are associated with a higher risk of complications?

Participants will:

Receive a midline catheter during surgery under general anesthesia.

Undergo ultrasound-guided assessment of the catheter site immediately after placement, 24 hours later, and before the catheter is removed.

Be monitored for any complications related to the catheter, including infection, blood clots, or blockage.

This study will help identify which factors increase the risk of complications, improving the safe use of midline catheters in pediatric patients.

Inclusion Criteria:

• Pediatric patients under 18 years of age
• Scheduled to undergo general anesthesia for surgery at Seoul National University Children's Hospital.
• Clinically indicated for midline catheter insertion as determined by the attending anesthesiologist.

Exclusion Criteria:

• Patients requiring central venous catheter (CVC) insertion instead of a midline catheter.
• Known coagulation disorders.
• History of severe thrombosis.
• Any other conditions that, in the investigator's judgment, make the patient unsuitable for the study.

The study will include pediatric patients under 18 years of age who are undergoing general anesthesia for surgery at Seoul National University Hospital and require midline catheter placement. This population is selected to investigate the incidence and risk factors for complications associated with midline catheter insertion in pediatric patients.