Clinical and Technological Approaches to the Prehospital Diagnosis of Large Vessel Occlusion

E ndovascular thrombectomy is highly effective for the treat- ment of acute ischemic stroke because of proximal large vessel occlusion, 1 but the treatment effect falls rapidly with time. 2 Almost all patients with severe stroke are transported by an emergency medical service (EMS), which is independently associated with reduced time to treatment.3 Nevertheless, delays are frequent in patients arriving for endovascular thrombectomy via secondary transport from another facility.1 To reduce time to treatment, some jurisdictions are exploring redirect policies, whereby patients bypass a closer primary stroke center and are instead transported directly to endovascular-capable facilities.4 Instituting a pathway for hospital bypass is a complex undertaking that involves the coordination of diverse stakeholders.4 Core components include patient selection criteria, interfacility agreements (eg, transfer and repatriation), paramedic training, and outcome evaluation.Approaches to patient selection have drawn recent interest, particularly in the use of simplified standardized clinical examinations for the diagnosis of proximal large vessel occlusion.In this review, we review current clinical and technological approaches to patient selection and discuss implementation in the context of jurisdictional features.The database search terms for this review article are provided in the online-only Data Supplement. Diagnosis: Foundation for TriageProximal large vessel occlusion is the substrate for endovascular thrombectomy-field diagnosis of large vessel occlusion is the sine qua non for hospital bypass.In this section, we discuss important caveats in prehospital diagnosis and follow with a review of specific clinical and technological approaches. CaveatsThree caveats apply to the interpretation of studies of diagnostic tests for transport decision making: First, diagnosis is primarily a means to support transport decision making, not an end.If 2 diagnoses share the same transport destination, then it might not be so important to distinguish between them.For example, distinguishing between intracerebral hemorrhage (ICH) and large vessel occlusion may be of little practical value if either would be transferred to a comprehensive center for advanced care.This pragmatic perspective is easy to overlook if singularly focused on the usual benchmark of diagnostic accuracy.Second, if the objective of transport decision making is to identify treatment candidates, it must be emphasized that diagnosis alone does not establish eligibility.Other factors, such as deficit severity, premorbid function, or the extent of ischemic injury, contribute to treatment decision making.Considering diagnostic and eligibility factors together may improve the specificity of selection criteria over diagnosis alone.Finally, the distinction between proximal and nonproximal large vessel occlusion is arbitrary.The classification of M1-middle cerebral artery and terminal internal carotid artery occlusions is not controversial, but the desirable classification of M2-middle cerebral artery occlusions is uncertain.Ideally, equipoise for this anatomic boundary would be recognized in the development and evaluation of diagnostic strategies.