Final answer:
After ensuring high-quality CPR is performed on a pulseless and apneic child with established vascular access, next interventions include using an automated external defibrillator (AED) if available and administering appropriate medications as per advanced pediatric life support guidelines.
Step-by-step explanation:
When you arrive on the scene to a 4-year-old child who is pulseless and apneic, with high-quality CPR being performed and vascular access established, the next intervention would likely involve advanced life support measures which could include the use of medications and possibly the use of an automated external defibrillator (AED). High-quality CPR should be continued with minimal interruptions, and if an AED is readily available, it should be used according to the pediatric algorithms provided in life support guidelines. In a professional healthcare setting, lifesaving drugs and the presence of a healthcare professional to provide advanced interventions would be the next steps in the management of the child's condition. It is important to follow the guidelines outlined by official pediatric advanced life support courses, which are endorsed and provided by organizations such as the American Heart Association or equivalent bodies in different countries.