This may lose a few non-technical people, with terms like “coronary perfusion pressure”, but bear with me. This excellent video drives at the heart of what CPR is, why it’s so important to saving the life of a cardiac arrest victim, and why over the past 8 years chest compressions have increased in importance. Yes, humans require oxygen in our brains and vital organs to survive, but the role of ventilations in most cardiac arrest situations is minimized.
In simpler terms, chest compressions are used to circulate blood when the heart is not beating. Any interruption to chest compressions stops the blood circulation, and blood flow ramps up when compressions start again. 
Yes, we need oxygen, and yes we need to shock with an AED. Otherwise, try to limit interruptions to the chest compressions. When your heart and lungs are working, does your heart stop for 10-12 seconds every 18 seconds?