Final answer:
The appropriate therapy for the unresponsive and apneic 3-year-old child receiving CPR is to continue high-quality CPR and use an AED if available. The initial defibrillation dose should be 2 J/kg, following up to 4 J/kg for subsequent shocks if needed.
Step-by-step explanation:
In the case of the 3-year-old child who is unresponsive and apneic and receiving CPR with bag-mask ventilation, the best course of action would be to continue high-quality CPR. If the patient is in cardiac arrest, the use of a defibrillator is essential. Automated External Defibrillators (AEDs) are accessible in many public places and are designed to be user-friendly so that even laypersons can use them effectively. They provide verbal instructions for use and can automatically determine the heart rhythm and apply a shock at the appropriate energy and waveform. CPR should be sustained until the child shows signs of recovery or until a healthcare professional determines the next steps. For a pediatric patient like the one described, the initial defibrillation dose should be 2 J/kg, followed by up to 4 J/kg for subsequent shocks if needed.