In which of the following situations can an AED be used?

The use of an Automated External Defibrillator (AED) is indicated in a patient who is in cardiac arrest. In this critical scenario, the heart is not pumping effectively, often due to a life-threatening arrhythmia such as ventricular fibrillation or pulseless ventricular tachycardia. The AED works by analyzing the heart's rhythm and delivering an electric shock if necessary to restore a normal rhythm.

In contrast, an AED is not suitable for a conscious patient experiencing trouble breathing, as they are still responsive and do not require defibrillation. Similarly, an unconscious child who has a pulse does not require an AED, because their heart is functioning, albeit they are unresponsive, and other interventions would be more appropriate, such as assessing airway and breathing. Lastly, a conscious adult experiencing chest pain may be experiencing angina or a myocardial infarction, but unless they show signs of cardiac arrest, an AED is not warranted in this situation either. In summary, the AED is specifically designed to be used when there is a confirmed cardiac arrest, making that scenario the only appropriate choice among the options presented.