The goal of this clinical trial] is to evaluate the efficacy and safety of the ultrasound-guided "Modified Dynamic

Needle Tip Positioning Short-Axis, Out-Of-Plane" (MDNTP-SAOP) technique compared to the "Conventional, Short-Axis, Out-Of-Plane" (C-SAOP) technique for femoral arterial cannulation performed by anesthesia residents in children. The main question it aims to answer is:

What is the time required for attempted femoral arterial cannulation by anesthesia residents at the first puncture site?

Researchers will compare the efficacy and safety of MDNTP-SAOP versus C-SAOP methods for femoral arterial cannulation performed by anesthesia residents in infants and children undergoing cardiac surgery.

Participants will be randomized to either the MDNTP-SAOP or the C-SAOP group. Intraoperatively, time taken for attempted cannulation by the resident at the first site of femoral arterial puncture, number of attempts at arterial cannulation, and number of cannulae required for successful cannula insertion will be recorded. Adverse events will be monitored on postoperative days 1 and 3. The insertion site will be examined for thrombosis, hematoma, infection, or limb ischemia distal to the insertion site

Background: Arterial cannulation in infants and children can be challenging, even for the most experienced provider. The femoral artery, preferred over the radial artery for its size and stronger pulsation, serves as the access site in infants and children undergoing cardiac surgery at our institution. While ultrasound-guided techniques have improved cannulation success compared to the conventional palpation technique, there is limited comparative research on different ultrasound-guided methods, namely "Modified Dynamic Needle Tip Positioning, Short-Axis, Out-Of-Plane" (MDNTP-SAOP) method versus "Conventional, Short-Axis, Out-Of-Plane" (C-SAOP) method, specifically for the pediatric age group, done by anesthesia residents.

Specific Aims: This study aims to evaluate the efficacy and safety of the ultrasound-guided MDNTP-SAOP technique compared to the C-SAOP technique for femoral arterial cannulation performed by anesthesia residents in children. The primary objective is to measure the time taken for successful cannulation at the first femoral arterial puncture site, with secondary outcomes assessing the number of attempts, first-attempt success rates, total cannulae used, and complications such as hematoma or thrombosis.

Methods: This prospective randomized controlled trial will include 80 children under 12 years of age scheduled for cardiac surgery. Participants will be randomized to either the MDNTP-SAOP or the C-SAOP group. This study will be double-blinded: Patients and research members will be blinded to the group allocation. Intraoperatively, time taken for attempted cannulation by the resident at the first site of femoral arterial puncture, number of attempts at arterial cannulation, and number of cannulae required for successful cannula insertion will be recorded. Adverse events will be monitored on postoperative days 1 and 3. The insertion site will be examined for thrombosis, hematoma, infection, or limb ischemia distal to the insertion site.

Analysis: Statistical analysis will involve continuous variables reported as means with standard deviations and analyzed using t-tests, while categorical data will be summarized as counts and percentages and examined using chi-square or Fisher's exact tests where appropriate. Non-parametric data, such as the number of attempts, will be reported as median and range. The significance level will be set at p < 0.05. The cumulative success percentage and time to successful cannulation will be analyzed using Kaplan-Meier survival curves and compared between groups using log-rank tests.

Significance: If the MDNTP-SAOP technique demonstrates a significantly shorter time to successful cannulation and lower complication rates relative to the C-SAOP method, it may provide a new standard for training anesthesia residents in the pediatric age group. This could ultimately enhance patient safety and improve clinical outcomes in pediatric cardiac surgery.

Inclusion Criteria:

• Infants and children under 12 years of age.
• American Society of Anesthesiologist (ASA) physical status II-IV.
• Patients with congenital heart disease undergoing cardiac surgery who do not have existing arterial line access.

Exclusion Criteria:

• Need for emergency surgery.
• Hemodynamic instability.

This study will be double-blinded: Patients and research members will be blinded to the group allocation.