Kevin S. Attenhofer, MD
The spectrum of acute ischemic stroke (AIS) care begins well before the emergency room. EMS first responders are often the first to examine the patient and consider the diagnosis of stroke. There are multiple triage scores and systems in place to assist EMS. Options include the Cincinnati Prehospital Stroke Scale (CPSS), Face Arm Speech Test (FAST), Los Angeles Prehospital Stroke Screen (LAPSS), etc. Most of these scales focus on identifying common findings of subcortical strokes (facial droop, hemiparesis). In 2014, Spanish researchers created and published the Rapid Arterial Occlusion Evaluation (RACE) Scale, which included cortical, as well as subcortical, exam findings to aid with pre-hospital identification of patients with higher likelihood of having a large vessel occlusion (LVO). In addition to facial palsy and hemiparesis, the RACE scale also scores gaze deviation, aphasia, and agnosia.
Clinical implications of the RACE scale are unclear. One ongoing clinical trial, RACECAT, is comparing direct transfer of patients with a high RACE score (> 4) to an endovascular center versus taking these patients to the closest acute stroke center (without endovascular capabilities) with subsequent “drip and ship” of patients determined to have an LVO. With those results not expected until 2020, Schlemm et al have implemented a conditional probabilistic model to calculate probabilities of good outcome (modified Rankin Scale ≤ 2 after 3 months) for triage of AIS patients with unknown vessel status to either a “mothership” approach (direct to endovascular center) or “drip and ship” approach.
They modeled a geographic environment containing one primary stroke center (PSC) and one comprehensive stroke center (CSC). Probabilities of good outcome for the mothership and drip and ship approaches are modeled as a function of 3 transport time variables (scene to PSC, scene to CSC, transfer time between hospitals) and the score of the RACE scale. Various treatment scenarios were created according to the time-based eligibility for the 2 treatment options (thrombolytic and thrombectomy).
Scenario I: Within window for tPA at PSC or CSC, transfer for EVT possible from PSC
Scenario II: Within window for tPA at PSC but not CSC, transfer for EVT possible from PSC
Scenario III: Within window for tPA at PSC or CSC, can’t transfer for EVT within treatment window
Scenario IV: Within window for tPA at PSC but not CSC, can’t transfer for EVT within treatment window
Optimal treatment scenario-specific RACE cutoff scores (the lowest RACE score, x, for which all RACE scores ≥ x would be associated with a higher average probability of good outcome under the mothership approach) were calculated.
Schlemm et al found that the RACE score at which the mothership approach begins to outperform the drip and ship approach is a moving target. In settings with a shorter distance between hospitals and a slower PSC in terms of thrombolysis and onward transfer, the optimal treatment scenario-specific RACE cutoff score is lower. While newly emerging data may change this practice in the future, they based their calculations on a requirement of groin puncture within 6 hours of symptom onset. Extending this window shifts more patients into treatment scenario models I and II, which favored higher RACE cutoff scores. We look forward to results of upcoming clinical trials, which are applying this scale to real-world clinical practice.