In the case of an unresponsive patient with no pulse, what should be initiated immediately?

In the scenario of an unresponsive patient with no pulse, the immediate priority is to start CPR and attach an Automated External Defibrillator (AED). This is because the lack of responsiveness and pulse indicates that the patient is in cardiac arrest, and immediate intervention is crucial to provide artificial circulation and increase the chances of survival.

Starting CPR ensures that blood continues to circulate to vital organs, especially the heart and brain, while the AED can analyze the heart's rhythm and deliver a shock if needed. The combination of these actions is the cornerstone of advanced life support protocols and significantly improves the likelihood of a successful outcome.

Other options, like notifying the nearest hospital or providing medication, while important in the broader context of emergency response, do not take precedence when the patient's life is at immediate risk due to cardiac arrest. These steps can be taken after ensuring that basic life support measures, like CPR and defibrillation, are underway. Portable oxygen therapy is also not the primary action in this critical situation, as ventilation is secondary to ensuring circulation first.