You do not need to give rescue breaths. Hands-only CPR \u2014 continuous chest compressions without rescue breaths \u2014 is recommended by Resuscitation Council UK for bystanders who are untrained, unwilling to give rescue breaths, or unable to do so.
In the first few minutes after a cardiac arrest, the blood still contains enough oxygen to supply the brain and heart if compressions are delivered promptly and continuously. Stopping to give rescue breaths interrupts blood flow and is less important than maintaining continuous, high-quality compressions.
If you have been trained in CPR and are confident giving rescue breaths, a ratio of 30 compressions to 2 rescue breaths is recommended. But if you are not confident with rescue breaths, do not let that stop you from doing compressions \u2014 hands-only CPR is highly effective and far better than doing nothing.
The only situation where rescue breaths are considered more important is cardiac arrest in children, where the arrest is more likely to be caused by a breathing problem. In this case, if you can, five initial rescue breaths followed by 30:2 CPR is recommended \u2014 though again, compressions alone are better than nothing.