Medic 12 and Engine 14 respond to a possible stroke at a private residence. Upon arrival, Engine 14 finds a 64-year-old female lying on her couch. The patient is conscious but is having difficulty communicating with the firefighters. The patient’s husband states she complained of a headache and weakness that started about two hours ago. At that time, he noticed she had slurred speech but did not want him to call an ambulance. He helped get her to the couch so she could lie down. When her speech difficultly worsened (about 15 minutes ago), he decided to call for help.
When paramedics from Medic 12 arrive, they find a conscious patient with no observable respiratory distress. The patient’s blood pressure is 150/94 mm Hg, the pulse rate is 92, the respiratory rate is 16 and the room air pulse oximetry value is 95 percent. The head-to-toe exam is unremarkable for trauma. In addition to the dysarthria, the patient has a positive arm drift and right-facial paresis. The point-of-care glucose reading is 89 mg/dL and the patient’s ECG shows sinus rhythm with no ectopy.
As the firefighters prepare the patient for transport, Medic Sanchez attempts to pinpoint the time the patient last appeared normal. The patient’s husband was initially unsure but remembered it was just after his watch alarm sounded, which reminds him to take his medication. The alarm was set for 8 a.m., which was 2 hours and 25 minutes ago.
During 25-minute transport, the patient rests comfortably. Medic Sanchez notifies the receiving primary stroke center and activates the stroke alarm. Upon arrival, the emergency department staff performs a quick evaluation and transfers the patient to the radiology department where the patient undergoes emergency computerized tomography. Following the CT scan, the patient is transferred back to the ED. The ED physician continues the stroke assessment using the National Institute of Health Stroke Scale. In the meantime, the neuroradiologist examines the CT scan and excludes hemorrhage, demarcated infarction or other pathological findings, but does find evidence of a hyperdensity in the left middle cerebral artery suggestive of occlusion.
It has now been 3 hours and 45 minutes from time zero, the moment the patient was last seen normal. The neurologist and ED physician agree that since the patient has evidence of a large vessel occlusion, she should probably receive mechanical recanalization at a comprehensive stroke center about 40 minutes away. However, both also agree the patient should receive bridging IV-thrombolysis as quickly as possible.
The ED staff begins IV thrombolysis and arranges critical care transport to a comprehensive stroke center located about 30 miles away. There, the neurointerventionalist and vascular neurologist provide mechanical recanalization and intra-arterial thrombolysis at 5 hours and 30 minutes from time zero. Over the next several days, the patient’s neurological symptoms improve rapidly and upon discharge on the eighth day, the patient has minor facial paresis, mild to moderate dysarthria, and mild hemiparesis in the upper extremities (NIHSS = 5).
Despite the patient’s improvement over the course of hospitalization, the medics wonder if the outcome would have been better if the patient had received IV thrombolysis even sooner.
Study review of mobile stroke unit impact
Researchers in Germany conducted the Prehospital Acute Neurological Treatment and Optimization of Medical care in Stroke (PHANTOM-S) study to investigate the impact of the world’s first mobile stroke unit on treatment time and safety [1]. More than a decade before, researchers proposed the creation of a mobile stroke unit (MSU) that would reduce the interval from symptom onset to treatment decision for patients having acute ischemic stroke [2]. The proposed MSU would be equipped with a CT scanner and point of care laboratory testing that would allow the ambulance staff to determine which patients were eligible to receive thrombolytic therapy before and during transport to a stroke center. The MSU was created and operated through a joint effort between a stroke research center in Berlin, the fire brigade, and two commercial companies who supplied telemedicine services and biomarker assays [3].
The staff for the MSU consisted of a neurologist, a paramedic and a radiology technician. In addition to the diagnostic equipment, the MSU contained telemedicine technology that allowed the MSU staff to consult with a remote neuroradiologist who could review the results of the CT scan and provide input on the appropriate field therapy.
Study period randomization consisted of four-week blocks of MSU availability and non-availability. During the available weeks, dispatchers in the emergency call center (similar to a 911 system in the United States), would use a scripted questionnaire to identify patients with a suspected stroke. In those instances, the dispatchers would send a normal emergency response consisting of first responders and a paramedic-staffed ambulance along with the MSU. When the MSU arrived, the neurologist assessed the patient while the first responders and paramedics provided routine prehospital care. If the assessment suggested acute ischemic stroke, the staff moved the patient to the MSU and performed the necessary POC laboratory tests and non-contrast CT scan. The neurologist then transmitted the results of the CT scan to a remote neuroradiologist for consultation. If both agreed on the results, and after verifying absence of exclusion criteria, the MSU staff initiated thrombolytic therapy and began transport to the nearest stroke center.
During the randomized weeks when the MSU was not available (control group), patients received the normal emergency care by first responders and paramedics. Researchers could then compare alarm to treatment intervals between the two groups to determine how much time the MSU concept could save.
Results of mobile stroke unit concept
During the 21-month study period, the emergency call center activated the stroke dispatch protocol almost 7,100 times. The patients were evenly distributed between MSU weeks and unavailable weeks (3,668 vs. 3,440, respectively). After assessment and pre-determined exclusions, 192 patients received thrombolytic therapy in the field and 218 patients received thrombolytic therapy in the hospital.
For the primary outcome variable, patients treated in the field received thrombolytic therapy 25 minutes earlier than patients treated in the stroke center. This resulted in 10 additional patients receiving thrombolytic therapy in the field who likely would not have received the drugs in the hospital because of the 4.5-hour administration window recommendation by ILCOR and the AHA [4]. In addition, when compared to normal care, deployment of the MSU resulted in a 50 percent increase in the use of thrombolytic therapy. Finally, careful and controlled field administration of thrombolytic medication incurred to significant risk of intracerebral hemorrhage or seven-day mortality.
What the MSU research means for you
The time dependent nature of the benefits of IV thrombolytic therapy for the management of acute ischemic stroke is well established [5]. Results from a pooled analysis of seven randomized-controlled trials involving IV thrombolysis for acute ischemic stroke indicates the chances of having a favorable outcome slowly diminish throughout the first 4.5 hours following symptom onset and become undetectable beyond that point [6]. For every minute a large vessel stroke remains untreated, the patient will lose approximately 1.9 billion neurons, which is roughly equivalent to 3 weeks of normal brain aging [7]. Thus, the sooner a patient can receive proper treatment, the greater the chances of optimizing the outcome. The greatest benefit occurs in patients treated within the first 90 minutes from symptom onset [8].
Acknowledging the time-sensitive nature of stroke care, the American Heart Association/American Stroke Association recommends a door-to-needle time of 60 minutes or less [9]. This period is meant to represent the interval from when the patient arrives at the ED door until the administration of IV thrombolytic therapy. Unfortunately, most patients suffering from acute ischemic stroke do not receive IV thrombolytic therapy within the recommended time frame. In a recent analysis of over 25,000 patients treated within three hours of symptom onset at over 1,000 hospitals in the United States, only about one-fourth (26.6 percent) had door-to-needle time intervals or 60 minutes or less [10].
Even in situations where hospitals can routinely meet the recommendations for door-to-needle times, prehospital factors constitute a significant source of delay from symptom onset to treatment for patients suffering from acute ischemic stroke [11]. Prehospital delays are significant enough to exclude about 50 percent of patients from being considered for thrombolytic therapy [12], although some data indicates the exclusion percentages may be much higher [13-15]. In an Australian study, only 52 percent of the emergency calls reporting symptoms consistent with stroke were made within the first hours after symptom onset [16].
There are two major categories of prehospital delays; those that result from symptom onset until someone notifies the EMS system and those that occur between the time EMS is notified and when patients are delivered to the stroke center. Pre-EMS notification delays primarily include the public’s general lack of knowledge about the warning signs of stroke [17-20]. In a sample of patients hospitalized following an acute ischemic stroke, only 37 percent were able to identify two or more stroke warning signs, and 35 percent could not identify even one stroke warning sign [21]. Only about one-fourth of patients suffering a stroke correctly attribute their symptoms to the condition [22]. Adding to this warning sign recognition failure, patients lack sufficient information about the importance of accessing the emergency response system. In one study, 80 percent of patients with an eventual diagnosis of stroke called their family physician rather than an ambulance to report the problem [23].
EMS assessment and transportation factors further contribute to delays in receiving prompt thrombolytic therapy. For patients ultimately discharged with a diagnosis of stroke, EMS responders failed to recognize the stroke in 40 percent of the cases [24]. Paramedics cite the diversity of stroke presentation, language barriers and alcohol or drug influence as confounders to assessment accuracy [25]. The use and documentation of a prehospital stroke screening tool improves diagnostic accuracy among EMS personnel [26]. Distance is another delaying factor, with fewer than 1 in 4 Americans (22.3 percent) living within 30 minutes of a primary stroke center [27]. Two-thirds (66 percent) of all patients in the United States with a discharge diagnosis of acute ischemic stroke in the Medicare Provider and Analysis Review database had geographic access to a primary stroke center within one hour by ground ambulance [28]. However, that percentage rose to 91 percent when including an air transport option.
The MSU concept offers one potential solution to the time problem common in the treatment of acute ischemic stroke [29]. This concept is more than just a mobile CT scanner. The MSU concept offers specially trained personnel and equipment which can provide remote diagnosis and evidence-based management to patients who might otherwise miss an opportunity for definitive treatment. Providing thrombolytic therapy before arrival in the ED has the potential to reduce neurological damage caused by stroke beyond any other therapies currently available in the field.
Limitations of the present MSU study
One limitation in this trial lies in the randomization process. Randomization that produces the least amount of bias (error) provides every individual an equal opportunity to be allocated to the treatment or the control group. Rather than randomize by individual, this trial randomized by week. This means that during the weeks the MSU was not available, it was impossible for any patient meeting the inclusion criteria to be randomized to the treatment group. Although the amount of bias may be small, it is present nonetheless.
Another limitation of this study lies in the fact there was only one MSU in operation at the time of the study. All of the patients included in the data analysis lived within 16 minutes of the station that housed the MSU. Whether that subgroup of patients was diverse enough to represent the entire population of patients in the city suffering from stroke is a matter of speculation. It is possible that placing the MSU in another area with a different subgroup of patient could yield different results.
Summary
Mobile stroke unit response significantly decreases the interval from symptom onset to the initiation of thrombolytic therapy without an increased risk of adverse events. More studies are needed to assess the generalization of these results to a larger population of patients suspected of having an acute stroke. Although at least three mobile stroke units currently operate in the United States (Houston, Cleveland, and Denver) [30], researchers in Houston are conducting the first study in the United States to compare outcomes between acute ischemic stroke managed by a mobile stroke unit and those receiving standard EMS management [31]. The trial is expected to end in early 2021 [32].
The author has no financial interest, arrangement, or direct affiliation with any corporation that has a direct interest in the subject matter of this presentation, including manufacturer(s) of any products or provider(s) of services mentioned.
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