Response Time Realities: The Scientific Evidence

Ask any EMS system in the U.S. about the quality of their performance, and almost invariably, one of the first benchmarks discussed is response time. But is that truly a measure of system quality? More importantly, does response time (RT) even matter in patient outcomes? How did response times become the predominant measure of system quality? How do we change our community’s understanding of what really matters and ultimately transform from being evaluated based on the effectiveness of a process–to the impact we have on patient outcomes?

How did we get here?

The closest thing we have to a “national standard” for response time is the “eight minute” standard (or 8:59) for ALS ambulances. How did this standard come about? Here are some hints. It was the year that the Ford Pinto was the best-selling car, Jimmy Carter was president, John McEnroe won the U.S. Open and the band Chic topped the Billboard charts with the song “Good Times.” Yep, 1979.

 

That year, the Journal of the American Medical Association published a study by the research team of Eisenberg, Bergner and Hallstrom called “Cardiac Resuscitation in the Community: Importance of Rapid Provision and Implications for Program Planning.¹” In the study, the authors found “if CPR was initiated within four minutes, and if definitive care was provided within eight minutes, 43% of patients survived. If either time was exceeded, the chances of survival fell dramatically.”

 

In the study, “definitive care” was defined as defibrillation. At that time, only paramedics could defibrillate. So voilà , the eight-minute standard for ALS was born.

 

To make matters worse, we as an industry, then used the concept of response time as a competitive determinate of success–even vowing to meet or exceed response time standards in an effort to win the right to serve communities. So in a way, the use of response times to measure a quality EMS system is a monster of our own making.

Scientific reality check

EMS has a history of implementing new systems or products based on perceived value. It has not been until recently that we started to focus on the science of service delivery. The same should apply to response times. Thankfully, several published studies seem to demystify the effect of response times to patient outcomes. Here are some highlights:

  • Paramedic response time: Does it affect patient survival?²
    This study evaluated 9,555 patients in Denver to see if there was any correlation to patient outcomes based on response times. The study concluded that “a paramedic response time within eight minutes was not associated with improved survival to hospital discharge after controlling for several important confounders, including level of illness severity. However, a survival benefit was identified when the response time was within four minutes for patients with intermediate or high risk of mortality. Adherence to the eight-minute response time guideline in most patients who access out-of-hospital emergency services is not supported by these results.”
  • Lack of association between prehospital response times and patient outcomes.³
    The authors of this study looked at the current 10:59 response time standard in an urban system and evaluated the patient outcomes of 746 patients experiencing life-threatening conditions. The authors concluded that “compared with patients who wait 10:59 minutes or less for ALS response, Priority 1 patients who wait longer than 10:59 minutes could experience between a 6% increase and a 4% decrease in mortality, and do not have an increase in critical procedures performed in the field. Our data are most consistent with the inference that neither the mortality nor the frequency of critical procedural interventions varies substantially based on this pre-specified ALS RT (response time).”
  • Optimal defibrillation response intervals for maximum out-of-hospital cardiac arrest survival rates.4
    As part of the well-known Ontario Prehospital Advanced Life Support (OPALS) Study, the authors published the following conclusion with regard to response times: “The eight-minute target established in many communities is not supported by our data as the optimal EMS defibrillation response interval for cardiac arrest. EMS system leaders should consider the effect of decreasing the 90th percentile defibrillation response interval to less than eight minutes.”
  • Response time effectiveness: Comparison of response time and survival in an urban EMS system.5
    This study reviewed 5,424 patient transports in an urban EMS system with a 10:59 response time standard and evaluated 71 patient encounters that resulted in death. The conclusion they reached was that “emergency calls where RTs were less than five minutes were associated with improved survival when compared with calls where RTs exceeded five minutes.

Although variables other than time may be associated with this improved survival, there’s little evidence in these data to suggest that changing this system’s response time specifications to times less than current, but greater than five minutes, would have any beneficial effect on survival.”

What about trauma?

We have often held that the “golden hour” was paramount in significant trauma cases. So one would presume that the “need for speed” would clearly be required in trauma cases, right? Several studies examined the correlation between response times and patient outcome for these types of incidents.

 

A study in Denver examined 3,940 trauma cases, all of which were transported to a Level 1 trauma center.6 The results from this study showed that “after controlling for other significant predictors, there was no difference in survival after traumatic injury when the eight-minute ambulance RT criteria was exceeded (mortality odds ratio 0.81, 95% CI 0.43—1.52). There was also no significant difference in survival when patients were stratified by the injury severity score group.”

 

The authors concluded that “exceeding the ambulance industry response time criterion of eight minutes does not affect patient survival after traumatic injury.”

 

In 2008, the U.S. Metropolitan Municipalities’ EMS Medical Directors (a.k.a. the “Eagles Consortium”) published a position paper in Prehospital Emergency Care regarding the issue of response times measures and the evaluation of the quality EMS system.7 The most notable quotes from their position paper are the following:

  • “In many jurisdictions, response-time intervals for advanced life support units and resuscitation rates for victims of cardiac arrest are the primary measures of EMS system performance;”
  • “The association of the former with patient outcomes is not supported explicitly by the medical literature, while the latter focuses on a very small proportion of the EMS patient population and thus does not represent a sufficiently broad selection of patients.”
  • “Over-emphasis upon response-time interval metrics may lead to unintended, but harmful, consequences (e.g., emergency vehicle crashes) and an undeserved confidence in quality and performance;”
  • “Much of the clinical research utilized to establish an acceptable advanced life support (ALS) response time interval was conducted in a period when only paramedics could operate a defibrillator, and the compression component of basic cardiopulmonary resuscitation (CPR) received much less emphasis.”
  • “Now that basic life support (BLS) providers and lay rescuers can provide rapid automated defibrillation as well as basic CPR, the relative importance of the ALS response-time interval has been challenged, both for cardiac arrest as well as for other clinical conditions;” and
  • “Many communities are still not measuring the intervals for the most important predictive elements for optimal outcome: time elapsed until initiation of basic chest compressionsand time elapsed until defibrillation attempts.”

What’s the harm?

Aside from the obvious risks of driving with lights-and-sirens to calls in which we will have minimal patient outcome impact, providing an eight-minute ambulance response time standard results in two major drawbacks. First, the community invests significant dollars for the cost of readiness to assure the ambulance can get there in eight minutes. Second, we need many more paramedics in the system staffing those ambulances. Is it better to have an experienced paramedic arrive in 15 minutes, or an inexperienced one arrive in eight minutes (or less)?

 

During his keynote address at the 2011 EMS Today Conference & Exposition in Baltimore, Myers expressed his opinion that it’s clinically beneficial to have fewer paramedics with more experience caring for patients.

 

Further, the Eagles Consortium stated in their previously mentioned position paper, “pragmatically, considering that ALS cases constitute a small minority of all EMS 9-1-1 responses, adding more paramedics into the system may actually reduce an individual paramedic’s exposure to critical decision-making and clinical skill competencies.”

What to do now?

As a profession, we need to unwind the clock and focus on the things that truly make a difference in patient outcomes. Imagine what we could do with a few million dollars saved by not having as many ambulances in our EMS systems.

 

We could fund more BLS first response units in order to get hands on the chest more reliably within five minutes. We could invest in public education campaigns for Continuous Chest Compression Resuscitation or even campaigns teaching chest pain or stoke patients to call 9-1-1 before their symptoms render interventions futile. Perhaps funds could even be used to invest in community health initiatives to prevent the 9-1-1 call by helping patients navigate our healthcare system and keep themselves healthy enough that they don’t need our services.

References

  1. Eisenberg MS, Bergner L, Hallstrom A. Cardiac resuscitation in the community: Importance of rapid provision and implications for program planning. JAMA.1979;241(18):1905—1907. doi:10.1001/jama.241.18.1905
  2. Pons PT, Haukoos JS, Bludworth W, et al. Paramedic response time: Does it affect patient survival? Acad Emerg Med. 2005;12(7):594—600. doi:10.1197/j.aem.2005.02.013
  3. Blackwell TH, Kline JA, Willis JJ, et al. Lack of association between prehospital response times and patient outcomes. Prehosp Emerg Care. 2009; 13(4):444—450. doi:10.1080/10903120902935363
  4. De Maio V, Stiell I, Wells G, et al. Optimal defibrillation response intervals for maximum out-of-hospital cardiac arrest survival rates. Ann of Emerg Med. 2003;42(2):242—250. doi:10.1067/mem.2003.266
  5. Pons P, Markovchick V. Eight minutes or less: Does the ambulance response time guideline impact trauma patient outcome? J Emerg Med. 2002;23(1):43—48. doi:10.1016/S0736-4679(02)00460-2
  6. Myers JB, Slovis CM, Eckstein M. Evidence-based performance measures for emergency medical services systems: A model for expanded EMS benchmarking. Prehosp Emerg Care. 2008;12(2):141—151. doi:10.1080/10903120801903793

 

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