You can do "Hands-Only" CPR where you just push, and no breaths. As was mentioned above, basically heel of hand centered on sternum at the 'nipple-line' and just push, 100 times/min. about 2" deep... keep going.
If you give breaths it's 30 compressions and then 2 breaths. (I'd just do 'hands-only' since air is forced in and out with each compression anyway)
P.S. It's NOT normal to break ribs, if you're in the right location and pushing the right depth you should NOT break ribs... if you hear popping or cracking it's more likely it's cartilage separating, not a big deal, and even if you break a rib, you just keep going.
For 'traumatic full-arrest' such as someone in cardiac arrest after a motorcycle crash, the chance of survival is TERRIBLE, since some injury requiring surgery has probably caused massive hemorrhage leading to the cardiac arrest, but CPR is indicated anyway, and there's always a chance it's not trauma related, that they had a heart attack causing them to crash.
I've been a Paramedic since 1980. Former L.A. City Fire Dept.
P.S. The VAST majority of people 'actually' in cardiac arrest do NOT survive, you have to defibrillate them within less than 5 min. of the event to have much chance to save them. Most dead people stay dead. Getting a defibrillator to them QUICK is the key to them surviving, CPR won't do it by itself... for every minute that goes by that they are not defibrillated there's a 10% less chance they'll live, CPR or not.
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