How long before an unexpected critical event or actual cardiac arrest does a patient's baseline begin to deteriorate?

The answer to this question is a mean of 6.5 hours.

Cardiac arrest is a situation when the heart loss its function of pumping blood in the body. The main cause of cardiac arrest is due to coronary artery disease. Some of the causes of cardiac arrest are heart failure, lack of oxygen in the body, and due to a plenty of blood loss. If a person is under cardiac arrest and not treated immediately, the patient will die.    

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.