San Francisco sends out seven ambulances in response to people thought to be in cardiac or respiratory arrest for every one person that is actually in cardiac arrest, according to a new study of the city’s Emergency Medical Dispatch system.

The results reflect an issue faced by emergency departments around the world: how do you decide where to send a limited number of ambulances and paramedics?

“Using resources most effectively - that’s the name of the game,” Dr. Jeff Clawson told Reuters Health. Clawson, who was not involved in the current study, contributed to the first emergency medical dispatch system and is now with the National Academies of Emergency Dispatch in Salt Lake City, Utah.

In many cities, when a 911 call is made, a computer dispatch system uses the caller’s answers to a set of questions to categorize the call based on the kind of emergency and how serious it is. This prepares ambulance crews for what they will find at the scene and tells them if they need to use lights and sirens to get to the patient as fast as possible.

It also helps emergency departments use their ambulances and their crews most efficiently. “It’s expensive to send an ambulance plus sirens to every call,” Dr. Nicholas Johnson, the study’s lead author and then a medical student at the University of California, San Francisco, told Reuters Health. “There’s a finite number of ambulances. The goal ... is to make sure those ambulances are in the right place at the right time.”

Johnson and Dr. Karl Sporer, the vice chair of EMS and Disaster Medicine at UCSF, analyzed data from 911 calls for over 100,000 patients that were made over a year and a half in San Francisco. For each call, they compared how a patient was categorized by the dispatcher and the computer system with what paramedics reported when they arrived at the scene, looking specifically at cases of cardiac arrest - when the heart stops pumping blood effectively, throwing off circulation and the flow of oxygen to the brain.

The majority of cardiac arrests, as predicted, were assigned by the dispatch system to a group that included cardiac and respiratory arrests or death. But six out of seven calls in this category weren’t actually cardiac arrests.

Additionally, some patients who had been categorized for unconsciousness or breathing trouble were also found to be in cardiac arrest, as well as others that hadn’t been categorized by the system at all - probably because the call had been about another emergency, like a fire, the authors report in the journal Resuscitation.

Cardiac arrests are the highest priority of a dispatch system, Sporer told Reuters Health. Patients in cardiac arrest require immediate treatment if they are going to recover. So one goal of any emergency dispatch system is to make sure that every potential cardiac arrest gets an ambulance with lights, sirens, and an experienced crew.

But no dispatch system can perfectly determine who is in cardiac arrest and who isn’t. Sporer, who also works for the San Francisco Fire Department, said that the city ends up sending an ambulance with lights and sirens to more than 90 percent of patients who turn out to be in cardiac arrest. “That’s room for improvement, but we did pretty darn good,” he said. “What’s the price you pay for that? You send lots of people to calls and they turn out not to be in cardiac arrest.”

The authors did not determine what was wrong with patients who didn’t turn out to be in cardiac arrest despite the initial assessment, but Sporer said he is following up with a study that will track those other outcomes.

Johnson, who is now a resident in Emergency Medicine at the University of Pennsylvania, thinks other cities may benefit from similar studies. “This is a useful way for people who are involved in the administration of the emergency medical system to take a look at their own systems,” he said.

SOURCE: Resuscitation, online July 17, 2010.
By Genevra Pittman