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Prehospital stroke diagnosis and treatment in ambulances and helicopters—a concept paper

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Abstract

Stroke is the second common cause of death and the primary cause of early invalidity worldwide. Different from other diseases is the time sensitivity related to stroke. In case of an ischemic event occluding a brain artery, 2 000 000 neurons die every minute. Stroke diagnosis and treatment should be initiated at the earliest time point possible, preferably at the site or during patient transport. Portable ultrasound has been used for prehospital diagnosis for applications other than stroke, and its acceptance as a valuable diagnostic tool “in the field” is growing. The intrahospital use of transcranial ultrasound for stroke diagnosis has been described extensively in the literature. Beyond its diagnostic use, first clinical trials as well as numerous preclinical work demonstrate that ultrasound can be used to accelerate clot lysis (sonothrombolysis) in presence as well as in absence of tissue plasminogen activator. Hence, the use of transcranial ultrasound for diagnosis and possibly treatment of stroke bares the potential to add to current stroke care paradigms significantly.

The purpose of this concept article is to describe the opportunities presented by recent advances in transcranial ultrasound to diagnose and potentially treat large vessel embolic stroke in the prehospital environment.

Introduction

The need to improve upon disparities that restrict rapid identification and treatment of acute stroke is obvious. Stroke is both the second most common cause of death and the leading cause of early invalidity worldwide [1]. In the United States, nearly 800 000 people suffer an acute stroke every year, and globally, stroke accounts for 5.5 million deaths per year. Tissue plasminogen activator (tPA) is the accepted criterion standard of stroke current stroke therapy and the only drug approved by the US Food and Drug Administration (FDA) [2]. Innovative neurointerventional techniques provide new treatment options by mechanical removal of the vessel occluding thrombus [3], [4], [5], [6].

Because of delays in access and lack of effective stroke systems, the number of patients currently receiving tPA ranges between 1.6% [7] and 9% [8] with an average of 3% to 4% of the global stroke population. The number of tPA-treated stroke victims who do show an improved outcome after 3 months varies between 30% [9] and 60% [10], depending on the literature cited. Two major limitations restricting the use of tPA are the time window (up to 4.5 hours after known onset of stroke symptoms) and the exclusion of an intracranial hemorrhage using cranial computer tomography (CT). The latter is the main reason why tPA can only be administered in the hospital because mobile CT units are not available. Exception of this rule is the mobile stroke unit, introduced by investigators at the Charité hospital in Berlin, Germany [11]. This unit carries a CT scanner, besides clinical chemistry capabilities, enabling the administration of tPA in the field. The concept of a mobile stroke unit, however, is rather cumbersome, expensive, requires greater manpower, and is not necessarily widely applicable, mainly because of the costs.

Neurointerventional techniques designed to mechanically retrieve vessel-occluding blood clots show great promise but are limited to highly specialized medical centers with on-call trained interventionalists. By far, major limitation, however, is the lack of recognition of stroke symptoms and the delayed presentation after acute stroke onset.

Effective stroke care is much more likely in large metropoles where prehospital transportation commonly averages 15 minutes or less [12]. According to a recent publication 80% of the US population is within 60 minutes of a stroke center for air medical transport [13]. Stroke victims in rural communities may encounter transports that take hours. The odds of good outcomes are significantly higher in industrialized countries where state-of-the-art care can be quickly accessed [14]. However, 85% of all strokes occur in low- to middle-income countries where 85% of the world's population resides [15]. The risk of stroke rises with increasing age. By 2025, more than 800 million senior citizens (age ≥ 65 years) will reside in developing countries, predominantly in Asia and Latin America [15]. Clearly, most of the world's stroke victims would benefit from quick, simple, and effective interventions.

In an effort to limit the time-dependent loss of brain tissue, any delay in diagnosis and treatment should be avoided and ideally started once the emergency call has been dispatched. In ischemic stroke, nearly 2 million neurons die every minute [16].

The purpose of this article is to describe the opportunities presented by recent advances in transcranial ultrasound to diagnose and potentially treat ischemic strokes in the prehospital environment.

Section snippets

Prehospital transcranial ultrasound

The body of literature demonstrating the use of portable ultrasound devices for early diagnostic assessment at the emergency scene or during transport is rapidly increasing [17], [18], [19], [20], [21], [22]. Yet, their use is far from being accepted or even considered as a standard tool for prehospital personnel. The range of potential diagnostic indications for prehospital ultrasound now includes focused sonographic assessment in trauma [22], [23], [24], [25], cardiac arrest [26], [27], [28],

Macrovasculature

It is known that ultrasound has the capability to mechanically disaggregate the fibrin network of a blood clot. The prothrombolytic effect of ultrasound in combination with tPA has been demonstrated [43], [44], [45], [46], [47], leading to a first clinical trial in humans in 2004. Alexandrov et al [48] showed that the time to MCA recanalization was significantly decreased when tPA was used in combination with 2 hours of continuous transcranial ultrasound exposure. In this study, diagnostic

Potential use of ultrasound for prehospital stroke treatment

The ultimate goal of definitive stroke care is the initiation of beneficial treatment at the earliest time possible. Based on preliminary data, ultrasound treatment could be initiated in as little as 10 minutes following the arrival of prehospital personnel. Confirmation or exclusion of a major vessel occlusion using transcranial ultrasound should not take longer than 2 minutes in most suspected stroke victims. Whether treatment might be initiated using the same diagnostic ultrasound device or

Conclusion

Time remains the most important denominator for successful stroke treatment. Yet, few strategies address stroke before the patient arrives at the hospital. The current curriculum stresses attention to basic life support activities (airway, breathing, and circulation), assessing blood glucose and administering supplemental oxygen, establishing an intravenous access, and expediting transport to a designated stroke center if one exists. Novel approaches have been either cumbersome and costly (such

Acknowledgment

The Prehospital Transcranial Stroke Diagnosis Using Ultrasound And Wireless Technology project at the University of California, San Diego, has been supported by the MedEvac Foundation International.

Philips Ultrasound, Bothell/Washington, USA, provides the portable duplex ultrasound device, equipped with 4G wireless capability, for the aforementioned project.

The Bavaria California Technology Center (BaCaTec) provides travel funds for the ongoing joint project between the University of

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