For the clinical benefit of intravenous thrombolysis "IVT" or intra-arterial thrombectomy "IAT" time is the most crucial factor. Reducing the time between stroke onset en treatment is therefore a major goal. Since IAT is only suitable for stroke due to large anterior vessel occlusion "LAVO" which is only performed in specialized comprehensive stroke centers "CSC", triage of LAVO-patients in the prehospital phase (i.e. in the ambulance) in order to directly allocate them to such a specialized CSC will save vital time (time=brain!). Several LAVO-prediction scales for clinical triage have been developed but most were tested in- hospital by experienced neurologists. Consequently, there is a great need for validation of these scales in the prehospital setting by Emergency Medical Services "EMS" personnel.

Objective: to recalibrate, validate performance and assess feasibility of several existing LAVO-prediction scales in the prehospital phase (i.e. assessment by EMS personnel).

Study design: multiregional, multicenter observational cohort study to investigate performance and feasibility of LAVO-prediction scales a.

Study population: all patients potentially eligible for IVTIAT according to the protocol used by EMS personnel except for when younger than 18 years.

The study will be conducted in two EMS regions: Hollands Midden and Haaglanden. In addition, all hospitals in these regions that treat over 30 patients per year with IVT will participate, including at least 1 CSC with IAT-availability per region. These hospitals are: Leiden University Medical Center "LUMC"; Alrijne hospital (location Leiderdorp); Haaglanden Medical Center (HMC+); Haga hospital; LangeLand hospital (LLZ) and Reinier de Graaf hospital (RdGG).

The observational design is pragmatic and reflects standard practice for acute stroke care.

inclusion: All patients with suspected stroke potentially eligible for IVT/IAT as estimated by the on-site EMS nurse.

A web based application is used that merely structures observations that are currently noted on transport charts. EMS personnel will have access to the web-based application via the iPad/tablet/smartphone/computer on which the EMS transport chart is already filled out as part of standard care. Or via their patient record as used in the ambulance.

The application will consist of the following items:

• EMS transport number
• time of symptom onset
• probability of LAVO estimated by EMS nurse
• 9-12 questions to structure clinical observations made by the EMS nurse.

The application will be straightforward and designed in close co-operation with EMS personnel. With the items acquired all prediction scales can be reconstructed.

Data of the application will be retrieved retrospectively and coupled with retrospectively collected data from the participating hospitals by a trusted third party

Inclusion Criteria:

• Acute stroke code activated by EMS personnel

Exclusion Criteria:

• Age <18 years

All stroke codes within the ambulance regions of the Emergency medical services Hollands midden or Haaglanden.