This all depends on what type of arrest the patient is in (V-fib/VT vs. asystole or PEA) as well as how they got there (trauma vs. medical or even hypothermia). Also depends on how the patient is responding to treatment, if at all. I've worked CORs for as little as one round of meds to as long a an hour or so. Usually, we work them until there is no longer any "workable" rhythm, and we no longer have any reasonable treatments that could make a difference. To some extent, family comfort with ending resuscitation also plays into this, but don't get trapped into continuing to work someone who obviously has no chance JUST because the family wants you to keep going. It is FAR better for the family to stop and explain to them that there was nothing more that could be done...as long as that's true!
Nate.