Which Prehospital Scale Best Flags Large
Vessel Stroke?

December 03, 2020

Seven different scales designed to identify patients with a symptomatic large anterior vessel occlusion (sLAVO) stroke in the prehospital setting all showed good accuracy, high specificity, and low sensitivity in a new study.

Two scales, the Los Angeles Motor Scale (LAMS) and the Rapid Arterial Occlusion Evaluation (RACE) showed the highest accuracy, although the RACE scale may require more focused training, the researchers found. 

"Our study is the first to our knowledge to provide external validation in the field as well as to offer head-to-head comparisons of several established sLAVO prediction scales," the authors report.

The study was published online November 30 in JAMA Neurology.

Dr Nyika Kruyt

Ambulance staff attending a patient with a suspected stroke have to decide which hospital to go to — a comprehensive stroke center where endovascular therapy can be performed or a primary stroke center just for thrombolysis and possible onward transfer for endovascular therapy if required, explained senior author Nyika D. Kruyt, PhD, Leiden University Medical Center, Leiden, the Netherlands. Only a small percentage of patients are eligible for endovascular therapy — those with a large anterior vessel occlusion.

"The time needed to transfer from a primary to comprehensive stroke center can be high even if the hospitals aren't that far from each other, because of preparing the patient for the transfer and waiting for an ambulance," Kruyt said. "It would be great if we could distinguish sLAVO patients in the field and allocate them to the appropriate facility.

"Several scales have been designed to be used by paramedics to identify these patients, but they haven't been validated in the field by emergency services ambulance workers. We conducted this study in order to validate these scales."

From a literature review published earlier, the researchers found seven clinical scales that were most likely to be used. Each scale consists of various different combinations of tests to assess characteristics such as aphasia and degree of paralysis. For the current study, all the clinical items involved in the different scales were listed in an application, and paramedics were asked to complete the application after patient assessment but before ambulance departure.

"Each scale did not have to be assessed fully by the paramedic, but full reconstruction of each scale was possible by combining items used in more than one scale; for example, motor strength or aphasia," Kruyt explained.     

The study was conducted between July 2018 and October 2019 in a large urban center in the Netherlands with a population of approximately 2 million people; it included two different emergency services, three comprehensive stroke centers, and four primary stroke centers.

The study comprised 2007 consecutive patients aged 18 years or older for whom an acute stroke code was activated and data on the scales were available.

The clinical observations made by the paramedics enabled reconstruction of seven prediction scales. In addition to the LAMS and RACE scales, these were:

  • Cincinnati Stroke Triage Assessment Tool (C-STAT)

  • Prehospital Acute Stroke Severity (PASS)

  • gaze-face-arm-speech-time

  • Field Assessment Stroke Triage for Emergency Destination

  • gaze, facial asymmetry, level of consciousness, extinction/inattention

Scale scores were linked to hospital data, which established whether the patient had a sLAVO or not.

Results showed that of the 2007 patients assessed, 158 (7.9%) had a sLAVO. Accuracy of the scales ranged from 0.79 to 0.89, with LAMS and RACE scales yielding the highest scores (0.89 and 0.88 respectively).

Specificity was high for all scales (range, 80%-93%), whereas sensitivity was low (range, 38%-62%), the researchers report.

Feasibility was measured by assessing how often each test was performed by the paramedics. 

"There is no point using a scale if some of the tests are only filled out 50% of the time," Kruyt noted. 

"Most scales were quite feasible — with each item being performed 80% of the time. That's pretty good," he said. 

The paramedics did not receive any specific training beforehand as the researchers did not want to influence the results. "So we think these results are applicable to other places," Kruyt commented. 

The RACE scale, among others, was found to be slightly less feasible. Neglect, "in which a patient is not aware of one side of his or her world, appeared to be difficult to assess, but with specific training that can be improved," Kruyt noted.

Applying LAMS to their cohort — an urban region with relatively short distances between primary and comprehensive stroke centers — indicated that:

  • 13 patients with sLAVO who first presented to a primary center would have benefited from direct allocation to a comprehensive center,

  • 17 patients with ischemic stroke treated with thrombolysis would have unnecessarily bypassed a primary stroke center,

  • and 38 patients without sLAVO (including stroke mimics) would have been unnecessarily allocated to a comprehensive center (including 6 patients with clinically severe intracerebral hemorrhage)

The researchers are now working to see if it is possible to construct a different combination of tests which may have an even higher accuracy than the original scales used, and if incorporation of other data on vital parameters such as blood pressure and the sudden onset of symptoms would improve performance further.

Recommendations Will Be Specific to Locality

Kruyt said it was difficult to make sweeping recommendations based on these results.

"For urban areas similar to ours we think it is wise to use LAMS or RACE scales to identify patients to be taken straight to the comprehensive center. But they are not 100% specific and some patients who are not eligible for endovascular therapy may be taken to a comprehensive center when they could have received care more quickly by going to a primary stroke center," he explained.

This is less important if the centers are close to each other, Kruyt noted, "but if the distance to the comprehensive center is quite long then these patients lose more time for thrombolysis."

"In general, time lost for endovascular therapy seems more clinically important than time lost for thrombolysis, but we also have to look at the numbers of patients in each category," he added.

The recent RACECAT study found that the approach of using the RACE scale to identify sLAVO patients who were then directed to a comprehensive center showed similar clinical outcomes as the strategy of taking all patients to the nearest stroke hospital.

But Kruyt pointed out that the RACECAT study was conducted in the Catalonia region of Spain — a more rural region than the large urban center in the Netherlands used for this study. "The RACECAT region was very different to ours. They had much longer distances involved and a large variation in driving times between hospitals. Their conclusion that going direct to 'mothership' was not worse even in such an area is interesting," he commented.  

Although distance is one important delaying factor, transfer times between hospitals is another important consideration, he said.

"We have a very well-organized system in the Netherlands but still it takes 50 to 60 minutes to transfer a patient from a primary to a comprehensive center even if the driving time is only 10-15 minutes. If we can get these times down, then the 'drip and ship' strategy could be a better option. In RACECAT, the primary stroke centers achieved impressive transfer times," Kruyt said.

"Tremendous Work"

In an accompanying editorial, Kori S. Zachrison, MD, Massachusetts General Hospital, Boston, and Pooja Khatri, MD, University of Cincinnati, Cincinnati, Ohio, say: "With no doubt, our ability to identify patients with stroke due to large vessel occlusion in the prehospital setting is of paramount importance," adding that the authors of the current study "do tremendous work in advancing the state of this science."

They estimate that using the most accurate scale (LAMS) rather than the least accurate (C-STAT) in this study in 1000 patients with a suspected stroke would result in 120 fewer patients (12%) being taken unnecessarily to a comprehensive stroke center.

The editorialists also suggest that more technological approaches could become available in the future, including noninvasive sensors to detect large strokes and smartphone applications to weigh various transport options — and even incorporate live traffic patterns.

"The solutions are undoubtedly local and any attempt at a one-size-fits-all approach is fraught," they stress. 

Noting that regional patient characteristics as well as local hospital resources and quality measures also need to be taken into account, they conclude that: "We must prespecify these guiding principles in nuanced and nimble ways."

The study was funded by grants from t he Netherlands Brain Foundation, the Netherlands Organization for Health Research and Development, the Dutch Innovation Funds, and Health~Holland. The study authors have disclosed no relevant financial relationships. Editorialists Zachrison and Khatri each have multiple disclosures. The full list can be found with the original editorial.

JAMA Neurol. Published online November 30, 2020. Abstract, Editorial

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