On entering an adult patient's room, a nurse finds the patient unresponsive, not breathing, and without a pulse. What is the nurse's priority action?

Current American Heart Association Basic Life Support guidelines for healthcare providers responding to an unresponsive, apneic, pulseless adult prioritize high-quality chest compressions as the first action once unresponsiveness and absence of pulse are confirmed. Beginning chest compressions immediately is critical because cerebral perfusion declines rapidly during cardiac arrest; every 10-second interruption reduces the chance of successful return of spontaneous circulation. In a healthcare setting, activating the emergency response system (calling a code) should occur simultaneously — ideally by directing a second rescuer to call while compressions begin — but compressions must not be delayed to make the call. Providing rescue breaths alone (without compressions) is not the recommended initial action. Opening the airway is incorporated into the compression-ventilation cycle after compressions are underway, not as the first priority. The 2020 AHA guidelines emphasize a compression-first approach (C-A-B rather than the older A-B-C) precisely because circulatory support is more immediately life-saving than airway management in witnessed adult cardiac arrest. Therefore, beginning chest compressions represents the nurse's priority action.