During adult CPR, as a second rescuer, you should prepare to administer two ventilations after:

• A. 30 chest compressions
• B. 5 chest compressions
• C. 15 chest compressions
• D. Every 5 seconds

Answer: (A)

In two-rescuer adult CPR, the cycle is high-quality chest compressions followed by a brief ventilation pause. After completing 30 chest compressions, you deliver two ventilations, then immediately resume compressions and repeat the cycle. This 30:2 rhythm maximizes blood flow to the heart and brain while providing oxygen, without excessive interruptions.

Ventilating after only a few compressions or every few seconds would disrupt blood flow too often, lowering perfusion. Ventilating every 5 seconds would also create too many breaths and keep stopping compressions, which isn’t as effective. So the best approach is to administer two ventilations after 30 chest compressions.