In terms of CPR, which of the following situations would result in the highest mortality?

The situation of unwitnessed arrest with no prior CPR results in the highest mortality because the absence of immediate intervention significantly reduces the chances of survival. When a cardiac arrest occurs, every passing minute without CPR decreases the likelihood of a successful resuscitation. This is largely due to the rapid onset of brain damage and the limitation of oxygen supply to vital organs.

In cases of unwitnessed arrests, there is a critical delay in recognition and response. If no bystander or emergency response is present to start CPR promptly, the individual is not receiving any life-saving measures, leading to a drastic decline in survival rates. The longer the heart goes without effective circulation, the lower the chances of preserving neurological function and life.

Other scenarios, such as witnessed arrests with immediate CPR or even witnessed arrests with delayed CPR, typically see better survival outcomes because they involve immediate or eventual intervention. Unwitnessed cases with prior CPR would also provide some benefit, as initial chest compressions can help mitigate some of the detrimental effects of the lack of circulation prior to advanced medical help arriving.