Since it is extremely rare for any crew to conduct more than one cardiac arrest on a given day, the randomized vascular access method will only apply to the first cardiac arrest of the day. As crews do not return to the distribution center until the end of a shift (12 hours), it will be impossible to select additional envelopes for subsequent patient encounters. Paramedics will proceed with vascular access per current MEDIC prehospital protocols for any further cardiac arrest resuscitations that day.