 An increasingly common addition to the EMS system is the use of highly trained dispatch personnel who can provide "pre-arrival" instructions to callers reporting medical emergencies.They use carefully structured questioning techniques and provide scripted instructions to allow callers or bystanders to begin definitive care for such critical problems as airway obstructions, bleeding, childbirth, and cardiac arrest.Even with a fast response time by a first responder measured in minutes, some medical emergencies evolve in seconds.