Research challenges link between quick EMS response and survival chances

By Margot Sanger-Katz
The Concord Monitor

CONCORD, N.H. — In 2002, emergency medicine specialists at the Denver Health Medical Center wanted to find out how much response times affected the survival of the major trauma patients they treated — often the victims of car crashes, gunshots and stabbings. They treated the kind of patients for whom every minute — they thought — would matter.

More Research Studies on the Response Interval – Clinical Outcome Relationship

By Mic Gunderson

This article from the Concord Monitor raises important questions about the relationship between response intervals and clinical outcomes. The author cited just one of several such studies that have been carried out over the past few years.

Here is a summary of some of the others from the peer-reviewed literature.

The Ontario Prehospital ALS (OPALS) Study Group publication entitled 'Optimal Defibrillation Response Intervals for Maximum Out-of-Hospital Cardiac Arrest Survival Rates1 ' examined 9,273 resuscitation cases from multiple cities in Ontario during a six-year time frame.

The average response interval was 6.2 minutes (90th percentile at 9.3 minutes). Their data correlated survival rates to 90th percentile compliance to various response intervals: 9 minutes (4.6percent survival), 8 minutes (5.9percent survival), 7 minutes (7.5percent survival), 6 minutes (9.5percent survival), and 5 minutes (12.0percent survival).

The investigators concluded that the 8-minute ambulance response interval target established in many communities is not supported by their data as the optimal EMS defibrillation response interval for cardiac arrest.

They suggest that EMS system leaders consider the effect of decreasing the 90th percentile defibrillation response interval to less than 8 minutes.

The study by Callaham and Madsen entitled 'Relationship of timeliness of paramedic advanced life support interventions to outcome in out-of-hospital cardiac arrest treated by first responders with defibrillators3' looked for the effect the interval between the arrival of first responder/defibrillators and paramedic advanced life support (ALS) interventions on outcome.

 The study concluded that faster response by medics, or any individual ALS intervention other than first-responder defibrillation, demonstrated no benefit in this urban population with short intervals between responder arrivals. Aggressive ALS increased the number of survivors but also decreased their neurological outcome quality.

A study by Pons and colleagues entitled 'Paramedic response interval: Does it Affect Patient Survival3?' concluded that response intervals within 8 minutes were not associated with improved survival to hospital discharge after controlling for several important confounders, including level of illness severity for multiple condition types including cardiopulmonary arrest and trauma.

A survival benefit was identified when the response interval was within 4 minutes for patients with intermediate or high risk of mortality.

Adherence to the 8-minute response interval guideline in most patients who access out-of-hospital emergency services is not supported by these results.

1 The Ontario Prehospital ALS (OPALS) Study Group: Optimal Defibrillation Response Intervals for Maximum Out-of-Hospital Cardiac Arrest Survival Rates. Ann Emerg Med. 2003;42:242-250

2 Callaham MJ, Madsen CD: Relationship of timeliness of paramedic advanced life support interventions to outcome in out-of-hospital cardiac arrest treated by first responders with defibrillators. Ann Emerg Med. 1996 May;27(5):638-48

3 Pons PT, Haukoos JS, Bludworth W, Cribley T, Pons KA, Markovchick VJ: Paramedic response time: does it affect patient survival?. Acad Emerg Med. 2005 Jul;12(7):594-600

Blackwell and Kaufman published a paper entitled 'Response Time Effectiveness: Comparison of Response Time and Survival in an Urban Emergency Medical Services System.4'

The authors concluded that when emergency calls had response intervals of less than 5 minutes, they were associated with improved survival when compared with calls where response intervals exceeded 5 minutes.

They acknowledged that variables other than time may be associated with this improved survival, but there is little evidence in these data to suggest that changing the study system’s response interval specifications (10:59 for life threatening emergency cases and 12:59 for non-life threatening case) to times less than current, but greater than 5 minutes, would have any beneficial effect on survival.

The cases types included all cases types – including cardiopulmonary arrest and major trauma. Feero and colleagues’ study, 'Does out-of-hospital EMS time affect trauma survival?5' tried to determine if out-of-hospital emergency medical services time intervals are associated with unexpected survival and death in urban major trauma. Of 848 major trauma cases, there were 13 (1.5percent) unexpected survivors and 20 (2.4percent) unexpected deaths.

Of those patients with complete EMS times, the mean out-of-hospital response interval was significantly shorter for the unexpected survivors (3.5 +/- 1.2 minutes v 5.9 +/- 4.3 minutes; P = .04). The mean EMS on-scene time interval (7.8 +/- 4.1 minutes v 11.6 +/- 6.5 minutes; P = .06) and the mean transport time interval (9.5 +/- 4.4 minutes v 11.7 +/- 4.0 minutes; P = .17) also favored the unexpected survivor group. Overall, the total EMS time interval was significantly shorter for unexpected survivors (20.8 +/- 5.2 minutes v 29.3 +/- 12.4 minutes; P = .02).

It was concluded that a short overall out-of-hospital time interval may positively affect patient survival in selected urban major trauma patients. In a different study by Pons and colleagues entitled 'Eight minutes or less: does the ambulance response interval guideline impact trauma patient outcome?6', the authors concluded, that there was no difference in survival after traumatic injury when the 8 min ambulance response interval was exceeded.

There was also no significant difference in survival when patients were stratified by injury severity score group. The authors assert that exceeding the commonly used ambulance industry response interval criterion of 8 min does not affect patient survival after traumatic injury.

From my own perspective, I do not think there is much of any evidence to support choosing 8 minutes over any other particular number for an EMS response interval target in order to improve outcomes.

Looking at each of these studies in detail, I did not see data showing a particular time frame have any particular significance over any other. For the most truly time sensitive cases, such as a witnessed onset cardiac or respiratory arrest, the sooner the better is what the data shows – and even in urban systems, we probably do not get there fast.

That's because the costs go up exponentially as the response interval target gets shorter and shorter. So, where a community chooses to set the response interval target, it becomes more of a financial and political question than a clinical one.

4 Blackwell TH, Kaufman JS: Response Time Effectiveness: Comparison of Response Time and Survival in an Urban Emergency Medical Services System. Acad Emerg Med 2002; 9:288–295

5 Feero S, Hedges JR, Simmons E, Irwin L: Does out-of-hospital EMS time affect trauma survival? Am J Emerg Med. 1995 Mar;13(2):133-5

6 Pons PT, Markovchick VJ: Eight minutes or less: does the ambulance response time guideline impact trauma patient outcome? J Emerg Med. 2002 Jul;23(1):43-8

Mic  Gunderson serves as the President of Integral Performance Solutions (formerly the emergency medicine, fire and 9-1-1 division of HealthAnalytics).  You can contact him at

But after studying two years' worth of their hospital's major trauma cases, the researchers found no effect. Patients who arrived at the hospital quickly fared no better than those who took longer to reach the emergency room. Confused by this result, the specialists widened their analysis to look at all the patients who came to the city's emergency rooms by ambulance. Again, the data showed, response time didn't matter. They looked at patients with heart attacks, respiratory problems and other life-threatening health emergencies. None found a correlation between response time and survival

"It's a patient satisfaction and public relations issue, but in terms of patient outcome," said Dr. Vincent Markovchick, who worked on the studies, "a very rapid response time makes no difference."

As municipalities in New Hampshire and nationwide have made efforts to improve the quality of their ambulance services, they have often looked to their response times as the best measure of performance. The federal government has set an eight-minute response time target that fire departments and rescue squads endeavor to meet, often at great expense. Response time is an easily measured, intuitive proxy for the quality of EMS care. But though research in EMS is limited, no major published studies refute the Colorado results. According to Markovchick, there's simply no science that supports the national standard.

"The eight-minute standard is a very arbitrary number that was established 20 or 30 years ago," Markovchick said. "It was a guess."

EMS is less than 40 years old, and it has developed without a lot of scientific guidance about best practices. For years, states failed to gather comprehensive information about system performance.

The latest research makes it difficult to know what investments will have the best payoff for communities hoping to improve their pre-hospital care. Studies show not just that expensive response time improvements may have limited benefit but also that investing in paramedic-level care may not be cost-effective.

The federal eight-minute response time target was built around one particularly life-threatening emergency: sudden cardiac arrest. For patients who suffer from cardiac arrest, every minute that passes until their hearts are shocked back into rhythm dramatically decreases their chances of survival. In the 1970s and '80s, studies suggested that if personnel could reach cardiac patients within eight minutes, they could save many of them.

The latest thinking is that for patients to have a decent chance of meaningful survival, they really should be shocked within four minutes of when their hearts stop beating. And that's not four minutes from when the ambulance is called; it's four minutes from the beginning of the event. Those cases represent less than 1 percent of all 911 calls. And overall, survival from this type of heart attack is less than 5 percent.

Most rural ambulance services have already dispensed with a four- or eight-minute standard. In a densely populated city, it's possible to keep drive times short by spreading ambulances around. When it takes 10 minutes to drive from the fire station to the edges of town, a one-ambulance community will necessarily take longer to reach some patients.

"I know people would like to see it quicker, but from a safety perspective, I don't know how much faster you'd like to see them driving," said Epsom fire Chief Stewart Yeaton.

But how long is acceptable? Should a volunteer department with a 15-minute response time invest in full-time staff to cut that number down to 12 minutes? The answers are hard to come by.

Most ambulance calls are for minor medical conditions where experts say a taxi ride would serve just as well. Patients with sprained ankles, broken wrists or kidney stones may prefer medical care right away, but a few minutes won't change their prognosis.

But there are certain medical conditions where EMS and emergency room doctors say they know minutes matter. In trauma cases, doctors talk about the "golden hour" in which a patient should reach an operating room at an appropriate hospital. (Despite the wide use of the term in the emergency medical community, studies have also failed to show any proof that an hour is a critical time - most trauma patients who die do so either more quickly or more slowly.)

Other time-sensitive emergencies, experts say, include strokes, respiratory distress and severe allergic reactions. But medical research has yet to establish firm standards for how long those patients can wait before it's too late to save them.

Several researchers said they doubt a few minutes of improvement on a rural response time would make much of a difference.

Locally, nearly every large municipal EMS department boasts paramedics on every ambulance. But research done by Dr. Ian Stiell and others involved in the large scale Ontario Prehospital Advanced Life Support studies suggests that it takes careful training and use of medics to show a benefit to patients.

Stiell's research, which is ongoing, initially showed no benefit to medic care when it looked across the range of health emergencies. But as he drilled down to particular kinds of care, the findings were different.

In cases of respiratory distress, patients had higher survival rates when they had access to advanced life support.

In trauma cases, their rates were lower.

"That was kind of disturbing," Stiell said.

Cardiac patients did about the same no matter who treated them. What mattered, Stiell said, was whether they were treated with CPR and a defibrillator quickly.

Paramedics are trained to perform myriad treatments that basic EMTs can't do: They can administer drugs, insert breathing tubes and start IVs. Those skills can benefit a patient who needs the right kind of speedy care, but only if the medic also has the judgment to know what treatment to offer and the skills to do it right.

"They can put the tube in, but that's only a tiny part of it. The sort of cognitive skill of when to put it in, that's far more important," Stiell said. "Just because you know how to put it in doesn't mean that's what you're supposed to do."

An error, either in judgment or technique, while performing advanced life support skills, can have catastrophic consequences. "At the basic level, it's pretty difficult to kill someone. At the medic level, it's pretty easy," said Weare EMS Capt. Bob DeStefano, who recently completed paramedic training.

Just as surgeons drive down their error rates the more frequently they perform a particular operation, paramedics have been found to be better at assessing critically ill patients and administering paramedic-level treatments the more often they do it. In rural settings, that level of experience can be difficult to maintain.

Rich Serino, the deputy administrator of FEMA, who until recently ran Boston EMS, said Boston's department thought carefully about the best way to use paramedics. Instead of putting a medic on every ambulance, he said, they opted to put one in every fourth ambulance. Basic EMTs respond to every emergency, and the paramedics back them up when they are needed.

Serino said the system, which has become a model, saves the city the expense of staffing as many medics, who command higher salaries because of their training. He said it also ensures the medics on staff see enough tough cases to keep their skills sharp.

Researchers and municipal EMS directors talk about the design of an overall EMS system - not reliance on any one measure - as the key to providing the best care to patients in trouble.

They all agree that staffing ambulances with skilled EMTs who could provide a reliable, predictable response was important. But they also agree those systems worked better on larger scales, where it was possible to measure outcomes and maximize EMTs' exposure to a variety of calls.

They pointed to a parallel body of research suggesting an ideal system can go beyond ambulances, particularly when it comes to cardiac patients. In recent years, manufacturers have developed automatic external defibrillator machines, or AEDs, that can be used by the lay public and work just as well as an EMT's paddles.

Markovchick said expanding the use of these machines could make a real difference in cardiac arrest survival. Put them in police squad cars, school gymnasiums, nursing homes and malls, he said, and teach people to use them.

One large study supports this approach. In Las Vegas, casinos collaborated to train all their security guards in how to use AEDs. By 2000, the survival of people stricken with cardiac arrest in the casinos improved to 53 percent of all cases - better than the survival rate for patients in hospitals - according to a study in the New England Journal of Medicine.

The city of Seattle encouraged community members to learn how to use AEDs and ensured that every high school student took a CPR course before graduation. A recent study showed that Seattle may be the best city in North America in which to suffer cardiac arrest - the city outperformed nine others in a study published in the Journal of the American Medical Association.

In rural areas, expanding access to CPR and defibrillators makes particular sense, experts said. "Anybody can do CPR," said Sue Prentiss, New Hampshire's EMS chief. "It doesn't take an EMT to do it. Anybody can use a defibrillator."

Copyright 2009 Concord Monitor

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