ADVERTISEMENT
Using Ultrasound for Stroke
Strokes are the third leading cause of death, with one American dying of stroke every 3.5 minutes.1 They are also the leading cause of disability. While EMS can use prehospital stroke scales to diagnose the presence of stroke reliably, imaging is needed to determine the specifics of the event, with the most important aspect being able to differentiate ischemic and hemorrhagic events.
Approximately 80% of strokes are ischemic in nature. At current, tPA administration is perceived as the “gold standard” of treatment in these strokes. In reality, only about 5% of stroke victims actually end up receiving thrombolytic therapy.1 Those who do show a high rate of complications, with only one of eight affected patients regaining 100% pre-incident function within three months of the initial insult. In total, approximately 50% face severe disability or death.2
EMS does have a positive effect on door-to-CT times and the rate in which patients receive thrombolytic therapy. Early notification has been shown to decrease door-to-CT time by 17% and nearly doubles the rate of tPA administration.3-5 There has been a recent trend of programs utilizing mobile stroke units, specialized head CT-equipped ambulances, postulating that they will further improve outcomes. Thus far, these mobile stroke units have been shown to decrease onset-to-thrombolysis times, with 35% of patients receiving tPA within 90 minutes with standard procedures versus 62% of those treated with mobile stroke units. Despite these numbers, no improvements in outcomes have been shown.6 Given the cost of mobile stroke units themselves ($1.5 million or more), plus the cost of operation (over $1 million/year), it becomes more difficult to see a true cost benefit in them. As with most anything else in medicine, surely, there must be a better way.
Enter point-of-care ultrasound. Many ultrasound systems are capable of performing Transcranial Doppler (TCD). TCD can be utilized in the field to diagnose a large number of ischemic strokes. Traditional TCD exams are time intensive, performed by a specialist and look at the entire vasculature of the brain through multiple windows. In our case we are looking at only the middle cerebral artery (MCA) through the temporal bone. This much more focused exam is sometimes referred to as Transcranial Color Coded Sonography (TCCS). Typically, we say that ultrasound waves are unable to penetrate bone; however, the temporal bone is thin enough that it can be used as a viable window. The culprit vessel in approximately 90% of all ischemic strokes is the MCA7 (if you’re keeping score at home, that’s around 2/3 of all strokes).
To perform TCCS, a phased array transducer is used in the Duplex Color Doppler mode. This mode registers blood flow and presents it in a color-coded fashion on top of the traditional black and white B-mode image. This allows for the highlighting of the vessels responsible for cerebral perfusion. In an ideal view, the window will reveal all three branches of the MCA as well as parts of the anterior cerebral artery (ACA) and the internal carotid.
As we are directly visualizing blood flow, an MCA with an occlusion present will simply not appear. Additionally, the steal effect will be noted. Since the same amount of blood is still present in the cerebral vasculature, the excess blood that would normally be flowing through the MCA is rerouted into collateral circulation, distending adjacent vessels, typically the ACA. In essence, another vessel “steals” the blood from the occluded MCA. Looking for these markers TCD has been shown to be about 90% specific for MCA occlusion. The downside is that the MCA is visible using this technique in only around 70% of the population, which may make some call into question the efficacy of TCD—after all, what would providers say if a valid 12-lead ECG could be performed on only 70% of the population? There is however a way to increase this number. By utilizing microbubble contrast—smaller than a red blood cell purpose-produced albumin-based spheres—the success rate is increased to close to 99%.
After ruling-in an MCA occlusion, treatment can theoretically progress as it would have by ruling-out hemorrhage in a mobile stroke unit—while it is true that there have been isolated cases of patients presenting with concurrent ischemic and hemorrhagic pathologies, the rate is statistically insignificant.8 Virtually all cases of intracranial hemorrhage in ischemic stroke are iatrogenic, stemming from reperfusion attempts.
Given that an appropriately equipped POCUS system costs ~$25,000, there is an obvious cost savings—even before factoring in the multitude of other indications that the equipment can be used for. To put it in perspective, about 80 ultrasound systems can be purchased for the cost of a $2 million mobile stroke unit, with a much lower annual cost to maintain them.
But there’s an even bigger bonus benefit to this diagnostic modality—that same POCUS unit has the potential to actually treat the occlusion. Sonothrombolysis has been shown to disrupt clots both on its own and as an adjunct treatment with traditional thrombolytics.9 In 2005 Eggers et al conducted a small 15-patient study in patients ineligible for tPA. The group receiving transcranial doppler experienced higher rates of vessel reopening and had better early functional outcomes.10 A larger phase 3 study of a similar hands-free device called the CLOTBUST ER trial is currently underway. While the exact mechanism of action is not fully understood, it is believed that both mechanical disruption from cavitation created by the ultrasound waves and by agitating the clot itself, exposing it to a greater number of intrinsic fibrinolytic enzymes, is responsible for clot degredation.11 While this treatment modality may not be quite ready for use in all ambulances yet, it is easy to see how a machine we should already be carrying may drastically change prehospital stroke care.
Diagnostic transcranial sonography is a bleeding edge use of ultrasound in the prehospital arena. While TCCS may already have been validated in the field by neurologists12 and be significantly easier to perform than a true TCD, it likely still lies at the very edge of what even the most aggressive EMS agencies are capable of. Still, with the prevalence of multi-million-dollar head CT ambulances popping up all over major cities, the ability to not only diagnose, but potentially treat the same strokes, without tPA, using massively cheaper equipment that also has so many other uses, that’s a hard deal to pass up.
References
1. Mazighi M, Derex L, Amarenco P. Prehospital stroke care: Potential, pitfalls, and future. Curr Op Neurol, 2010; 23(1):31–Saqqur M, Uchino K, Demchuk A, et al. Site of arterial occlusion identified by TCD predicts the response to intravenous thrombolysis forstroke. Stroke, 2007; 38(3):948–54.
2. Strbian D, Soinne L, Sairanen T, et al. Ultraearly thrombolysis in acute ischemic stroke is associated with better outcome and lower mortality. Stroke, 2010; 41(4):712–716.
3. Abdullah AR, Smith EE, Biddinger PD, et al. Advance hospital notification by EMS in acute stroke is associated with shorter door-to-computed tomography time and increased likelihood of administration of tissue-plasminogen activator. Pre Emerg Care, 2008; 12:426–31
4. Belvis R, Cocho D, Marti-Fabregas J, et al. Benefits of a prehospital stroke code system: feasibility and efficacy in the first year of clinical practice in Barcelona, Spain. Cerebrovasc Dis, 2005; 19:96–101
5. Kim SK, Lee SY, Bae HJ, et al. Pre-hospital notification reduced the door-to-needle time for IV t-PA in acute ischaemic stroke. Eur J Neurol, 2009; 16:1331–35
6. Functional outcomes of pre-hospital thrombolysis in a mobile stroke treatment unit compared with conventional care: an observational registry study, The Lancet 2016. DOI: 10.1016/S1474–4422(16)30129–6
7. Jichici D. Anterior Circulation Stroke. In Medscape. Retrieved from https://emedicine.medscape.com/article/1159900-overview.
8. Toyoda K, Kumai Y, Fujii K, et al. Simultaneous onset of haemorrhagic and ischaemic strokes in a haemodialysis patient Journal of Neurology, Neurosurgery & Psychiatry, 2002; 72:673-674.
9. Rubiera M, Alexandrov AV. Sonothrombolysis in the management of acute ischemic stroke. Am J Cardiovasc Drugs, 2010; 10(1):5–10.
10. Eggers J, Seidel G, Koch B, et al. Sonothrombolysis in acute ischemic stroke for patients ineligible for rt-PA. Neurology, 2005; 64(6):1052–4
11. Sonothrombolysis in acute large vessel ischemic stroke, Neurology India 2017. DOI: 10.4103/0028–3886.198176
12. Schlachetzki F, et al. Transcranial Ultrasound from Diagnosis to Early Stroke Treatment – Part 2: Prehospital Neurosonography in Patients with Acute Stroke – The Regensburg Stroke Mobile Project. Cerebrovasc Dis, 2012; 33:262–271.
Branden Miesemer, NRP, FP-C, is a flight paramedic in the Midwestern United States and an adjunct paramedicine instructor for several local colleges. He is an advocate for leveraging technology and social media to provide low-cost, cutting-edge medical education and training. Follow him online at EMSPOCUS.com, Facebook.com/emspocus and on Twitter at @emspocus.
Jason Bowman MS, FF/CCEMTP, is a 4th year medical student at Texas A&M going into emergency medicine. Prior to medical school, Jason was a firefighter and critical care paramedic for nearly 10 years. During this time he established the prehospital ultrasound program at Keller Fire Rescue in north Texas where he used ultrasound for cardiac arrest, heart failure, obstetrical emergency and to diagnose strokes in the field, among many other uses. Jason currently writes for resuscitationist.com and is part of the emspocus.com group. Follow him on twitter @texprehospital.
