Columns, Commentary, Patient Care

Stroke Triage: EMS needs a diagnostic tool that goes beyond a simple history & physical exam

Issue 5 and Volume 43.

As a young EMT and paramedic, I had relatively little education about acute myocardial infarctions. In the age of the 3-lead ECG, education was largely focused on arrhythmia detection and how to differentiate heart blocks, tachycardia and bradycardia. Detection of heart attack was largely based upon history and physical exam findings.

Three decades later, the thought of relying on a physical exam to diagnose a ST- elevation myocardial infarction (STEMI) is hard to imagine. Although we’ve made remarkable progress in the prehospital detection of STEMI, we’ve made significantly less progress in the diagnosis of acute stroke.

Identification Systems

Our initial focus on triage for stroke was the simple identification of stroke vs. stroke mimic, followed by establishment of systems for prehospital activation of stroke centers.

Our goal was to get patients to a center where they had established teams that could rapidly evaluate patients, provide a CT scan of the head to differentiate hemorrhagic from ischemic stroke, and administer intravenous fibrinolytics, such as tPA.

There have been multiple hospital and prehospital scoring systems to aid in the diagnosis of stoke and determination of stroke severity. Since the mid-1990s, the gold standard for evaluation of stroke has been the NIH Stroke Severity score. This 15-factor, 42-point score was designed to create a common language in the evaluation of stroke patients by correlating exam findings with a scoring system. This score has been a reliable tool in predicting outcomes from stroke, as well as responses to interventions like tPA.

Challenges in Differentiation

Although there’s been some progress in severity scoring and differentiating stroke vs. stroke mimic, differentiating hemorrhagic vs. ischemic stroke remains challenging.

There have been prehospital efforts to improve this differentiation, such as the introduction of the stroke ambulance equipped with a CT scanner. Although these scanners are increasing in popularity, the logistical and financial impacts make them unlikely candidates for widespread use. Some stroke ambulances can cost $1 million per unit, not including the staffing and equipment costs, estimated at $500,000 per year.

What’s desperately needed is a convenient way to differentiate stroke vs. stroke mimic, hemorrhagic vs. ischemic, and large vessel occlusion (LVO) from non-LVO infarction.

This is even more important now that recent publications have shown the significant benefit of identification of LVO and the time dependence associated with endovascular therapy.

A 2016 meta-analysis pooled data from major endovascular studies and revealed not only a significant benefit to endovascular thrombectomy, but also an important time- dependent association with improvement in disability from stroke.1

The study found that one in every 100 patients had a significant increase in disability for every nine minutes of delay in endovascular thrombectomy. Patients who received endovascular thrombectomy at 480 minutes had an almost 40% decrease in the chance of independent function at three months compared to those who received the therapy at 180 minutes from symptom onset.1

Some have argued that primary stroke centers can quickly screen patients and then transfer patients to a comprehensive center capable of thrombectomy therapy. In this study, there was a delay of up to one hour in reperfusion time among transferred patients compared to direct arrival patients.1

Advances in Triage

There are several biotech companies exploring out-of-hospital stroke triage that hold the potential for significant advancement. One concept involves the use of biomarkers associated with the immune response that results from acute strokes. Not only does this have the potential to detect stroke vs. stroke mimic, it may also be able to differentiate hemorrhagic vs. ischemic and LVO vs. non-LVO.

This technology has the potential to provide a highly sensitive and specific way for EMS providers to accurately triage and navigate our patients to the appropriate facility.

Another concept uses a modified and portable electroencephalogram (EEG) that can be easily carried in the back of an ambulance.

It uses an algorithm to diagnose stroke electronically, and it may also be able to differentiate between stroke types.

Though these technologies are still being developed, they offer hope for the future of rapid and accurate triage for stroke.

Due to time-dependent associations between appropriate intervention and outcomes, along with the significant morbidity, mortality and costs associated with stroke care in the United States, we can expect rapid and significant advancement in stroke triage in the coming years.

EMS needs a diagnostic tool that goes beyond a simple history and physical exam, so we can navigate our stroke patients to the closest facility that can provide the appropriate intervention for their stroke pathology.

Reference

1. Saver JL, Goyal M, van der Lugt A. Time to treatment with endovascular thrombectomy and outcomes from ischemic stroke: A meta-analysis. JAMA. 2016;316(12):1279–1289.