Abstract TP275: Modelling the Impact of Mobile Stroke Unit Dispatcher Accuracy on Patient Outcomes

Abstract

Introduction: Ischemic stroke with large vessel occlusion (LVO) cannot be definitively diagnosed without imaging. The Mobile Stroke Unit (MSU) has brought this capability (along with alteplase administration) to the field. In areas with widespread urban sprawl, having MSUs stationed in the community may improve patient outcomes. However, this is also dependent on how accurately dispatch can assess suspected stroke with LVO over the phone. We compare the probability of good outcome for patients taken direct to Comprehensive Stroke Centre (CSC) (mothership) vs utilizing a MSU at varying levels of dispatcher accuracy in identifying ischemic stroke with suspected LVO. Methods: Conditional probability models for patients with suspected LVO for mothership and MSU scenarios were generated. The positive predictive value (PPV) of dispatcher screening was varied from 25% to 75%. A sliding dichotomy was used to define good outcome, mRS 0-2 at 90 days was used for LVO patients and mRS 0-1 was used for non-LVO patients. Data from the HERMES collaboration was used for EVT patients, data from the Emberson meta-analysis (extrapolated to the HERMES population for LVO) was used for alteplase treated patients. Probability of good outcome for intracranial hemorrhage and stroke mimics was considered time invariant. Results: The results are visualized using temporal-spatial diagrams with one CSC and four MSUs stationed around the CSC with each MSU covering one quarter of the city. If dispatcher accuracy is poor the area where MSU predicts the best outcome is large as more non-LVO strokes, which benefit from fast alteplase, will be picked up. However, as dispatcher accuracy in identifying LVO increases the mothership areas also increase as the MSU would impose delays in these patients receiving EVT. Conclusions: The ability to accurately dispatch the MSU to patients with suspected LVO impacts transport decision making. This should be considered when designing a stroke system containing a MSU.