Patient Care

Mobile Stroke Units: A Device in Search of an Indication

If you’ve been to any regional or national EMS conference in the last two years, you’ve seen these mobile stroke units. They are beautiful large ambulances with the latest and greatest in modern technology including mobile CT scanners. Often, the name of a hospital is blazoned on the side. There is usually a staff member present to tell you how great these will be for your community. But are they? Where’s the science? What’s the cost? These are important questions that should be asked and answered before these devices are deployed on a widespread basis.

Although still somewhat controversial, therapies are now available to help reduce or mitigate the effects of an acute stroke. In many cases, these treatments can help the acute stroke patient to maintain a certain level of functioning. In some cases, such therapy can be lifesaving. But, it is not without significant risk. Today, there are several strategies available to treat an acute ischemic stroke. These include the administration of a thrombolytic (fibrinolytic) therapy such as recombinant tissue plasminogen activator (rtPA). More recently, several centers are now providing interventional neurology treatments where patients with emergent large vessel occlusion (ELVO) strokes are catheterized and receive endovascular thrombolytic therapy or other therapies into the affected artery in hopes of relieving part of the obstruction and restoring perfusion to the affected region of the brain.1

The interventional window for stroke therapy is 3 hours (4.5 hours in some centers) for providing definitive therapy for patients who have experienced an acute stroke. In some facilities, the interventional window has been further extended with specialized technologies.2 Certainly there are patients who benefit from interventional therapy for stroke. It’s now a diagnosis of the highest priority for many hospitals where patients are closely tracked to assure prompt intervention in case of a stroke. In fact, in some circles, it is almost a de facto standard of care that patients with selected stroke syndromes be offered thrombolytic therapy or other interventional therapy. The term “time is brain” has been utilized to emphasize the need for rapid diagnosis and intervention (if eligible) because reportedly 1.9 million neurons die each minute in which stroke is untreated.3

If it’s determined that a patient is a candidate for stroke therapy, it seems intuitive that the sooner the drug is administered, the better. This is very similar to the push to provide thrombolytic therapy and other therapies for ST-segment elevation myocardial infarction (STEMI). In fact, when rtPA was approved by the FDA in 1996, it was touted as a therapy for both STEMI and stroke. Thrombolytic therapy, in fact, had a high-level recommendation from the American Heart Association for stroke. However, further evidence did not show that stroke could be treated in a fashion similar to STEMI. The primary issue was that not all strokes are ischemic.

While approximately 87% of strokes are of ischemic origin (thrombotic or embolic), the remaining 13% or so are hemorrhagic. Because of this, the administration of thrombolytics without obtaining a correct diagnosis of stroke type could be fatal if the patient were to receive thrombolytics in the setting of a hemorrhagic stroke. The only way to determine with any degree of accuracy whether a stroke is ischemic or hemorrhagic is with CT imaging of the brain (and this is not 100% accurate). Thus, the decision to administer thrombolytic therapy to patients who are candidates for this is treatment is dependent upon the interpretation of an emergent CT image of the brain. Because it would be unwise and even dangerous to administer thrombolytics to stroke patients without a CT, strategies were developed to try to decrease the time it takes to make a definitive diagnosis. Thus, the idea of mobile stroke units with CT scanners was introduced.

The idea of placing CT scanners in an ambulance and taking the scanner to the stroke patient (instead of the stroke patient to the scanner) was introduced in Germany.4,5 These initial studies indicated that the administration of rtPA therapy for stroke in the prehospital setting was safe with a faster time-to-treatment and an increase in the overall treatment rate (21% to 33%). In these two initial studies, a stroke neurologist was part of the mobile stroke unit team.

The first mobile stroke unit in the United States was implemented in 2014 in Houston. The unit was placed in the Texas Medical Center complex. For the first two years, a stroke neurologist was aboard the unit in Houston. Now, there are approximately 20 mobile stroke units operating in the U.S. The units cost between $600,000 to $1,000,000 each, and the cost to operate these (for just 12 hours each day) is estimated at $950,000 to $1,200,000 annually.6 While reviews of this technology have been mixed, there are some questions that must be first asked and answered:

  1. Do patients benefit? This is the most important question, yet it is has remained unanswered. The limited studies to date have shown that the time to administration of thrombolytic therapy is shortened through use of mobile stroke units. However, the time may not be clinically significant. One study showed only a 15-minute time reduction to thrombolytic therapy administration using mobile stroke units. A Cleveland study showed a 42-minute reduction compared to standard care. A German study of 100 patients treated with either a mobile stroke unit or standard hospital therapy found a reduction in time to treatment for the group treated by the mobile stroke unit, yet there was no substantial difference in number of patients who received intravenous thrombolysis or in neurologic outcome.4,7 It has also been suggested that any improvement in outcomes with early rtPA administration may not actually represent bona fide improvement. In actuality, many of the patients deemed initially as having a stroke may actually be suffering a transient ischemic attack (TIA) and would have gotten better without treatment.8
  2. Is it worth the cost? Without a doubt, this is an expensive technology and there have been no studies that have demonstrated it to be cost-effective or even sustainable. EMS in the U.S. is grossly underfunded, yet money is available for mobile stroke units and medical helicopters—both of which lack any significant scientific evidence of improved patient outcomes. Why have these been introduced? First, as with any technology, it has to be tried and studied, and the initial mobile stroke units were operated by teaching hospitals as a research protocol. Other hospitals have now added mobile stroke units. The reasoning, unfortunately, is not altruistic. The competition between hospitals for patients in 2017 has reached a fevered pitch. They will do anything to get patients into their system. Nothing says “high-tech” like a mobile stroke ambulance or a medical helicopter. They know that once patients have gotten into their hospital system they will stay in the system. This is the real reason behind the introduction of expensive technologies into the prehospital setting that do not pay for themselves. They are simply loss leaders to get patients into the hospital system.
  3. Is staffing sustainable? Most mobile stroke units are staffed by neurologists or neurology residents in addition to support personnel. These physicians have the education and experience to make decisions regarding thrombolytic therapy. Replacing the stroke neurologist with paramedics or nurses using telemedicine has been suggested. However, this is limited by current technology. It takes a tremendous amount of bandwidth to transmit the CT images of the brain from a mobile stroke unit to a neuroradiologist at a remote site. If you also try to stream telemedicine between the mobile stroke unit and a stroke physician at the same time, communications would be virtually impossible. Presently, many of the mobile stroke units are only staffed at certain times of day and not available on a 24-hour basis. Unfortunately, strokes don’t just happen during working hours.
  4. Does the community benefit? A community with a mobile stroke unit does potentially stand to benefit from a shortened treatment time—especially in the case of ELVO strokes. However, most stroke units are now hospital-based and only have access to a very small geographic area. Also, there is a disproportionate number of strokes in certain ethnic groups and in lower socioeconomic areas. If this technology is to benefit the community, it must benefit all of the community and not just those near the hospital. This is an ethical issue that will have to be eventually addressed.
  5. Are stroke patients even candidates for interventional therapy? Not all stroke patients are eligible for thrombolytic therapy. In a recent study of 177,179 patients with a stroke who arrived within two hours of stroke onset and who met all other inclusion criteria, 65% of these patients had a contraindication or warning for rtPA use. The most common reason was improving symptoms (51%) which oftentimes is indicative of a TIA.9 The data available from the mobile stroke units, although limited, indicates that most patients encountered are not candidates for intravenous thrombolytic therapy. In fact, one mobile stroke team reported only treating 1.5 patients per week.10
  6. How educated are EMS providers on stroke identification (especially ELVO strokes)? Time and money are better spent on helping EMS personnel to identify strokes (especially ELVO strokes) and getting the patient rapidly to a full-service stroke center with a short door-to-needle time. The current literature shows that prehospital stroke identification schemes are not particularly great for identifying strokes. Perhaps there should be emphasis on identifying ELVO strokes since these are often easier to identify, more devastating, and stand to benefit more from thrombolytic or other interventional therapies. Scoring systems are being developed to help personnel identify ELVO strokes.

In summary, while mobile stroke units seem like a good idea and there is genuine hope that they will improve outcomes for selected stroke patients, there is not yet any evidence that this is the case. They are expensive and financially non-sustainable. Without widespread deployment, they stand to benefit few, if any, patients. The money spent on these devices would be better spent on improving the current EMS system including paramedic education, the availability of stroke centers, and on the early recognition of ELVO strokes.11

References:

1. Southerland A, Johnston K, Molina C, et. al. Suspected large vessel occlusion: Should emergency medical services transport to the nearest primary stroke center or bypass to a comprehensive stroke center with endovascular capabilities? Stroke. 2016;47:1965–1967.

2. Demaerschalk B, Kleindorfer D, Adeoye O, et. al. Scientific rationale for the inclusion and exclusion criteria for intravenous alteplase in acute ischemic stroke: A statement for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2016;47:581–641.

3. Saver J. Time is brain—quantified. Stroke. 2006;37(1):263–266.

4. Walter S, Kostopoulos P, Haass A, et. al. Diagnosis and treatment of patients with stroke in a mobile stroke unit versus in hospital: a randomized controlled trial. Lancet Neurol. 2012;11(5):397–404.

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

6. Bukata R. Are mobile CT stroke units worth the price tag? Emergency Physicians Monthly. 2017;(1):15–18.

7. Kunz A, Ebinger M, Geisler F, et al. Functional outcomes of pre-hospital thrombolysis in a mobile stroke treatment unit compared with conventional care: an observational registry study. Lancet Neurol. 2016;15:1035–1043.

8. Saver J, et. al. Time to treatment with intravenous tissue plasminogen activator and outcome from acute ischemic stroke. JAMA. 2013;309(23):2480.

9. Messé S, et al. Why are acute ischemic stroke patients not receiving IV tPA? Neurology. 2016;87(15):1565–1574.

10. Bowry R, Parker S, Rajan S, et. al. Benefits of stroke treatment using a mobile stroke unit compared with standard management: The BEST-MSU study run-in phase. Stroke. 2015;46:3370–3374.

11. Hastrup S, Damgaard D, Johnsen S, et. al. Prehospital acute stroke severity scale to predict large artery occlusion: Design and comparison with other scales. Stroke. 2016;47:1772–1776.