Final answer:
Change the compressions:ventilations ratio from 30:2 to 15:2
Step-by-step explanation:
When a 12-year-old child suddenly collapses, is unresponsive, apneic, and pulseless, and CPR is in progress, the next step after attaching the AED and receiving a shock recommendation is to change the compressions:ventilations ratio from 30:2 to 15:2. This means that the rescuer should deliver 15 chest compressions followed by 2 ventilations. This change allows for more frequent delivery of chest compressions, which is vital for maintaining blood circulation and oxygen supply to the body.