Patient Care

Prehospital Ultrasound Proves its Worth in the War Against Stroke

Issue 12 and Volume 41.

You respond to a 9-1-1 call for a 61-year-old woman experiencing right-sided weakness and trouble speaking. The onset of symptoms was 10 minutes prior to the 9-1-1 call.

The patient resides in a rural area, and it takes 30 minutes for your crew to reach her. You learn that she has a history of hypertension and has a history of cigarette smoking.

You note that the patient is hypertensive with a blood pressure of 170/96. When you complete your Cincinnati Prehospital Stroke Scale, you find she has weakness on the right side of her body in both the arm and the leg, and has difficulty finding words. You’re able to quickly begin transport and determine this patient would be best treated at a facility that specializes in stroke care. Such a facility is an hour’s transport time from the patient’s home.

The “time is brain” axiom is repeated over and over in your mind as you realize how much time will pass before this patient’s suspected stroke is confirmed with imaging and treatment can begin.

Discussion

Stroke is a devastating neurologic condition with an alarming prevalence. Each year, an estimated 795,000 people in the United States alone will suffer a stroke. Stroke accounts for one in every 20 deaths in the U.S., and someone dies of stroke in the U.S. every four minutes.1 One third of people who have had a stroke will be left with some degree of long-term disability.2

Eighty-seven percent of all strokes are ischemic, meaning that a clot or other occlusion to blood flow forms within an intracranial vessel, depriving the brain tissue of blood flow.1 If this obstruction isn’t rapidly relieved, damage to the brain will occur.

Figure 1: Distal MCA mainstem occlusion in a patient
with global aphasia and right-sided hemiparesis

Prehospital Ultrasound for stroke
(a) Prehospital TCCS showed a resistance profile only at the origin of the
left middle cerebral artery (MCA), (b) whereas flow in the contralateral
MCA was unremarkable. At the hospital, (c) a CT scan displayed a
dense artery sign (arrow), and (d) a CTA showed occlusion
of the MCA (arrow). Reprinted with permission.11

Although effective acute ischemic stroke treatments exist, all are time-sensitive. Thrombolytic medications that break down blood clots represent the mainstay of therapy for acute ischemic stroke. These drugs can be delivered systemically or at the site of occlusion by threading a catheter into the occluded vessel. For each of these approaches, however, the complication rate increases and the success rate decreases as time from symptom onset progresses.

For this reason, the rapid identification and treatment of patients experiencing ischemic stroke is critical.

The Evolving EMS Role

The prehospital management of stroke has focused on recognition. The Cincinnati Prehospital Stroke Scale (CPSS), Los Angeles Prehospital Stroke Scale (LAPSS), and Melbourne Ambulance Stroke Screen (MASS) are several scales utilized in the field to screen patients who may be experiencing an ischemic stroke.3–5

Although these scales have been prospectively validated to demonstrate the ability to detect patients experiencing symptoms that are worrisome for the possibility of stroke, it’s unclear that these scales contribute significantly more than provider judgement alone when it comes to stroke recognition.3

Many EMS systems utilize destination protocols that designate certain receiving centers (if such a resource is available in the community) once a patient is identified by providers as potentially experiencing stroke. These stroke centers are equipped with imaging technology, stroke pharmaceuticals, acute stroke treatment specialists and teams focused on stroke rehabilitation.

EMS care during rapid transport of these patients to stroke centers focuses around preventing complications such as aspiration, but the vast majority of actual treatment for stroke occurs after patient turnover at the hospital.

Thrombolytic medications remain a mainstay of treatment in acute ischemic stroke. Tissue plasminogen activator (tPA) is a commonly administered thrombolytic agent that works by catalyzing the conversion of plasminogen (an inactive precursor) to plasmin, an enzyme that breaks down clots in the body. When administered within the first three hours of symptom onset, patients experiencing an ischemic stroke are 30% more likely to have minimal or no disability three months after the event as compared to patients who received a placebo agent in similar clinical circumstances.6

Recent research has shown that the systemic administration of tPA may be beneficial even up to 4.5 hours after the time of onset of stroke symptoms.7 The administration of thrombolytic drugs in the prehospital environment for the treatment of acute ischemic stroke has been discussed. A 2014 study in Berlin (PHANTOM-S) examined the ability of a mobile stroke unit to decrease the time interval between when an emergency call was made and thrombolytic medication was administered.8

The results of this study demonstrated that the average time to administration of thrombolytic medication was significantly shorter when the patient’s stroke diagnostics were completed in the field with the mobile stroke team, although the researchers weren’t able to determine whether this decrease in alert-to-needle time made a difference in functional outcomes for the patients who were treated in the field.8

The mobile stroke unit utilized in the PHANTOM-S trial was rich with stroke expertise; a paramedic, a radiology technician, and a neurologist were on board the unit at all times.

The vehicle contained an onboard mobile computed tomography (CT) scanner and a point-of-care laboratory, and was telemedicine connected. Although staffing such a vehicle in most systems is unrealistic—a single vehicle outfitted in this fashion costs an estimated $1.4 million8—this study emphasizes that reframing the model of stroke care and bringing what are historically hospital-based capabilities into the prehospital setting can decrease the time to delivery of thrombolytic therapy and narrow the critical window of time in which patients experience cerebral ischemia.

Ultrasound Alternative

Although outfitting a mobile stroke unit with all the resources in the PHANTOM-S trial is presently outside of the budget of many agencies, a portable ultrasound machine may not be. New ultrasound technology has been developed to evaluate blood flow through the intracranial vessels. Transcranial color-coded sonography (TCCS) is a technique in which Doppler flow measurements are paired with ultrasound images. TCCS can be performed using a portable ultrasound machine to assess blood flow through cerebral vessels by utilizing a high-frequency linear ultrasound transducer applied to the skull.

There are various positions on the skull where the bone in thin enough to allow passage of ultrasound waves to assess several intracranial arteries.

Sound waves emitted by the ultrasound transducer interact with blood that’s flowing through these vessels at a certain velocity.

The ultrasound’s computer is programmed to convert these interactions into a color representation that’s overlaid on the ultrasound image of the vessel. These color images represent the direction and speed of blood flow. Flow through these vessels can be confirmed by visualizing the presence of color, whereas if color flow isn’t visualized, an occlusion of the vessel may be suspected. (See Figure 1, above.)

Research on TCSS has demonstrated a high degree of agreement between TCSS findings and imaging modalities often utilized in the hospital to diagnose stroke (e.g., computed tomography with angiography (CTA)9 and magnetic resonance imaging.10

A 2015 study in Regensburg, Germany, evaluated the accuracy of transcranial color-coded sonography (TCCS) performed in the field as compared to traditional in-hospital imaging modalities. Two paramedics, an emergency physician and stroke-specialty neurologist responded to emergency calls in this region in which a patient was experiencing neurologic symptoms. If a neurologic exam performed on scene indicated cerebrovascular occlusion, TCCS was performed. All patients for whom stroke was felt to be a possibility were transported to a stroke center and evaluated with definitive hospital-based imaging modalities.11

During the study period, the specialized prehospital team performed TCCS on just over 100 patients who met eligibility criteria. The diagnosis of ischemic stroke was made in 73 of those patients, whereas 29 patients were felt to have other conditions that mimic the clinical findings of stroke.11

The responders’ combined neurological and sonographic assessments led them to be able to detect 94% of those patients who were ultimately determined to be having a stroke. When the investigators narrowed their focus on how well prehospital TCCS findings for a major occlusion within the middle cerebral artery (MCA) or the anterior cerebral artery (ACA) correlated with advanced imaging at the hospital, they found correlation 98% of the time.11

Although a neurologist accompanied emergency crews and performed the prehospital TCCS, the authors suggest that transcranial ultrasound could be performed by a broader range of providers including paramedics with telemedicine support, and could be especially beneficial in rural areas where transport times to stroke centers are prolonged.11

Of note, 42% of the TCCS examinations were performed in the transport unit en route to the hospital, indicating that this exam can be performed in a moving ambulance, and any further delays in care can be averted.11

Conclusion

The study demonstrates the feasibility of prehospital TCCS assessment at both identification of acute ischemic stroke in the MCA distribution and decreasing alarm-to-needle time.11 This adds to the growing interest in improving the delivery of stroke care, in expanding the role of EMS providers to include more diagnostic modalities, and in the potential for ultrasound to significantly impact prehospital stroke care.

As interest in telemedicine builds, the possibility of prehospital providers one day being trained to perform TCCS in conjunction with telemedicine consultation with a neurologist is real. As more research on prehospital stroke treatment develops, the essential pieces of stroke diagnosis and treatment may continue to find their way outside of the hospital and into the hands of EMS.

In the race to restore perfusion to an ischemic brain, the minutes saved by performing diagnostic studies in the field and beginning treatment as soon as the diagnosis of stroke is confirmed could make a tremendous difference in outcome for patients who might otherwise suffer the devastating consequences of ischemic stroke.

References

1. Mozaffarian D, Benjamin E, Go A, et al. Heart disease and stroke statistics—2016 update: A report from the American Heart Association. Circulation. 2016;133(4):e38–e360.

2. Leal J, Luengo-Fernandez R, Gray A, et al. Economic burden of cardiovascular disease in the enlarged European Union. Eur Heart J. 2006;27(13):1610–1619.

3. Frendl D, Strauss D, Underhill B, et al. Lack of paramedic training and use of the Cincinnati Prehospital Stroke Scale on stroke patient identification and on-scene time. Stroke. 2009;40(3):754–756.

4. Bray J, Coughlan K, Barger B, et al. Paramedic diagnosis of stroke: Examining long-term use of the Melbourne Ambulance Stroke Screen (MASS) in the field. Stroke. 2010;41(7):1363–1366.

5. Kidwell C, Starkman S, Eckstein M, et al. Identifying stroke in the field: Prospective validation of the Los Angeles Stroke Screen (LAPSS). Stroke. 2000;31(1):71–76.

6. The National Institute of Neurological Disorders and Stroke rt-TPA Stroke Study Group. Tissue plasminogen activator for acute ischemic stroke. NEJM. 1995;333(24):1581–1587.

7. Hacke W, Kaste M, Bluhmki E, et al. Thrombolysis with alteplase 3 to 4.5 hours after acute ischemic stroke. NEJM. 2008;359(13):1317–1329.

8. Ebinger M, Winter B, Wendt M, et al. Effect of the use of ambulance-based thrombolysis on time to thrombolysis in acute ischemic stroke. JAMA. 2014;311(16):1622–1631.

9. Brusner A, Lavados P, Hoppe A, et al. Accuracy of transcranial Doppler compared with CT angiography in diagnosing arterial obstructions in acute ischemic strokes. Stroke. 2009;40(6):2037–2041.

10. Boddu D, Sharma V, Bandaru V, et al. Validation of transcranial Doppler with magnetic resonance angiography in acute cerebral ischemia. J Neuroimaging. 2011;21(2):e34–e40.

11. Herzberg M, Boy S, Holscher T, et al. Prehospital stroke diagnostics based on neurological examination and transcranial ultrasound. Crit Ultrasound J. 2014;6(1):3.