Final answer:
The next step in treatment for an unresponsive adult without breathing or a pulse is to perform cardiopulmonary resuscitation (CPR) immediately and continue until professional help arrives or the patient regains a pulse.
Step-by-step explanation:
If an adult victim is unresponsive, not breathing, and without a pulse, the next step in treatment is to perform cardiopulmonary resuscitation (CPR). This emergency procedure is crucial because cardiac arrest occurs when the heart no longer effectively pumps blood, and without immediate intervention, vital organs, particularly the brain, cannot function. Starting CPR within minutes is essential since brain cells begin to die after just a few minutes without oxygen. According to current standards, chest compressions should be at least 5 cm deep and at a rate of 100 compressions per minute, which coincides with the beat of the song "Staying Alive". CPR should be administered until the patient regains a pulse or until an experienced healthcare professional can take over.