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EMS Intervals & Associated Mortality


Review of: Newgard CD, Schmicker RH, Hedges JR, et al. Emergency medical services intervals and survival in trauma: Assessment of the "golden hour" in a North American prospective cohort. Ann Emerg Med. 2010;55:235–246.

The Science
This prospective cohort (pulled from a registry of adult patients) study aimed to address the issue of the “golden hour” and its relationship to trauma patient outcomes. The study analyzed response intervals and mortality among the patients with field-based physiologic abnormality.

The registry was populated from 146 EMS agencies that transported to 51 Level 1 and Level 2 trauma centers. Patients included in the study had one or more of the following physiological abnormalities: systolic BP ≤ 90, respiratory rate < 10 or > 29, GCS of ≤ 12 or advanced airway intervention. The outcome measure was hospital mortality.

Of the 3,665 patients analyzed for the study, 806 died. Analyses didn’t demonstrate a significant association between time and mortality for any EMS interval: activation (odds ratio [OR] 1.00; 95% confidence interval [CI] 0.95 to 1.05), response (OR 1.00; 95% CI 9.97 to 1.04), on-scene (OR 1.00; 95% CI 0.99 to 1.01), transport (OR 1.00; 95% CI 0.98 to 1.01), or total EMS time (OR 1.00; 95% CI 0.99 to 1.01).

The authors conclude no difference in intervals and mortality in trauma patients.

The Street

Medic Marshall: I’m not sure where to begin. This prospective cohort study captured a large population of trauma patients from many EMS services from Canada and the U.S. with a great amount of variation between them. The way the data was collected makes it extremely difficult to analyze. In the paper the researchers state, “It is possible that other factors, such as unmeasured confounders, selection bias, statistical approach, inclusion criteria, intervals assessed, or heterogeneity in the sample (variance), precluded our ability to show such an association [between time and outcome].” Although I applaud the investigators for trying, I really believe they failed to answer their research question.

And again, the issue of “ALS doesn’t matter in trauma care” is brought up by the investigators. Personally, I’m sick and tired of hearing “paramedics/ALS doesn’t make a difference.” I challenge anyone out there to research the decision-making and critical-thinking skills of paramedics compared to EMRs and EMTs. Sure, there are a few ALS skills that can be utilized in trauma care, but those skills can be life-saving (e.g, chest decompression).

Finally, the investigators failed to obtain injury severity scores (ISS) on each of the trauma patients. This highlights a key problem with trauma studies: No matter what you do, some patients are just going to die. It’s a fact. Because ISS is the accepted standard of measuring the severity of patient injuries, I see no reason to accept this study as truly meaningful or earth shattering. Furthermore, using hospital outcomes to measure effectiveness of EMS is bogus in my opinion. There are too many variables associated with care rendered in the hospital to actually link patient outcomes with prehospital care.

Doc Wesley: I’m astounded that the authors would state, “In this North American sample, there was no association between EMS intervals and mortality among injured patients with physiologic abnormality in the field.” That isn’t what this study proved. A more accurate conclusion would be, “There is no association between EMS intervals and mortality in systems with total EMS times less than 47 minutes.”

Table 1 of the article lists the various times associated with their trauma patients. This table presents the mean and what is called the IQR or Inter-quartile range. This isn’t the total range but is instead the middle 50% of the total range. The longest total EMS time in this range was 47 minutes. Then, they compared the patients in each quartile and found no difference in mortality and make the assertion that even the fourth quartile patients, who had total EMS time in excess of 120 minutes, have no difference in mortality than those with shorter times. Although this is true, as far as it goes, the patient groups aren’t the same. One striking difference is that the fourth quartile group was transported by helicopter from the scene 15% of the time while the helicopter was using less than 2% of the other 75% of patients. I have to wonder if air medical’s care improved survival in these patients.

If anything, this study confirms that the “golden hour” is indeed the goal and that our years of training and education have paid off by instilling into our providers the importance of delivering the multiple trauma patient to definitive care as quickly as possible.

I’m encouraged to see that an on-scene time average of 19 minutes wasn’t associated with poor outcomes as we all know that it’s virtually impossible to extricate, stabilize and initiate transport in less than 10 minutes—a benchmark many have proposed.

The important take-home message is that this study was a sampling of multiple services across Canada and the U.S. and may not reflect EMS as a whole. In particular, studies of rural services have shown that EMS interval is associated with mortality, and this should be taken into consideration when developing criteria for air medical evacuation of the multiple trauma patient.



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