When should a lifeguard initiate the use of an Automated External Defibrillator (AED)?

The correct answer is based on established CPR and emergency response protocols. A lifeguard should initiate the use of an Automated External Defibrillator (AED) when faced with an adult victim who is unresponsive and not breathing normally after emergency help has been called. This situation indicates that the victim may be experiencing a cardiac arrest, where immediate intervention is critical to increase the chances of survival.

Using an AED is crucial in this scenario because it can provide life-saving shocks to restore a normal heart rhythm. The AED should be used as soon as it is available, and following the appropriate guidelines for its use can significantly improve the victim’s chances of survival.

In contrast, the other choices do not adequately represent scenarios warranting immediate AED use. For example, a situation involving a child near the pool edge doesn't imply a medical emergency requiring an AED, and initiating its use when the victim shows signs of improvement contradicts the purpose of the AED, which is for unresponsive victims. Additionally, relying on the lifeguard's personal judgment without clear indicators could lead to delays in treatment when time is of the essence.