Geospatial Modeling of Stroke Care Accessibility

A series of polygons was calculated for the zones covered (isochrones) representing the distance that can be attained from each stroke treatment facility in a particular length of time. The first stage thus consists of listing and geolocalising each stroke treatment infrastructure. Thus, public hospital emergency departments, Primary Stroke Center (PSC) and Comprehensive Stroke Center (CSC) [35 (link)] in the Rhône and neighbouring counties were geolocalised using their precise postal addresses (Table 2).Table 2

Distribution of patient admission infrastructure

Infrastructure	County	Staff
Emergency department	Rhône (69)	7
	Ain (01)	3
	Saône-et-Loire (71)	6
	Isère (38)	7
	Loire (42)	6
PSC	Rhône (69)	2
	Ain (01)	1
	Saône-et-Loire (71)	1
	Isère (38)	2
	Loire (42)	2
CSC	Rhône (69)	1
	Ain (01)	0
	Saône-et-Loire (71)	0
	Isère (38)	1
	Loire (42)	1

Preliminary measurement of accessibility to facilities from all points in the network with 10, 20, 30, 45 and 60-min access time was thus calculated. These time steps were chosen after bibliographic analysis [7 (link), 16 (link)–19 (link), 36 (link), 37 (link)]. Each scenario was applied to this modelling.
Although it is pertinent to characterise the area according to the time required for travel from any point in the network to the treatment facility, it is even more interesting to model overall admission time. Treatment of stroke requires the best possible upstream taking in hand of the patient [4 (link), 38 (link)]. This means that it is necessary to know the pattern of the territory according to the type of transport and also the positions of stroke treatment facilities. In our case, the development of thrombectomy and recent studies have shown its advantages for patients [39 (link)–41 (link)] and modelling overall patient reception was performed using the location of the CSC. With this model it is possible to characterize the territory by care delays from the emergency call to the admission in nearest CSC. It is a global approach of care because all the times of pre-hospital emergency care for stroke patients are taken into account. The second phase of our study was therefore aimed at georeferencing each fire station in the Rhône and neighbouring counties, together with each SMUR team, using their precise addresses. After this georeferencing, supply zones were calculated for these facilities and then for each CSC to finally show total admission time—i.e. the estimated times from SMUR centres or fire stations to all the points in the network and then from any point to the CSC (Fig. 2). In this model, private car is not considered because it is not possible for patient to go directly to the CSC by his own. It was interesting to take intervention and triage times into account to better estimate the time. Thus, after a review of the literature, average time for ambulance dispatch, time spent at the scene and transport to a Comprehensive Stroke Center and intervention at the site of occurrence determined by Adeoye [19 (link)] were chosen (Fig. 2). The final times were calculated using the United States EMS (Emergency Medical Service) register for stroke cases alone.Fig. 2

Diagrammatic representation of overall journey time modelled according to the type of transport (SMUR and fire brigade)

This overall approach was represented on the basis of IRIS area units (Ilots Regroupés pour l’Information Statistique, small zones grouped for statistical information), the smallest administrative division of Insee (Institut National de la Statistique et des Etudes Economiques) and that respect demographic (populations of 2000) and geographic criteria [42 ]. This representation gives an accurate view and characterisation of areas according to access time to an CSC. For thrombectomy, discussions are in progress with regard to direct admission to CSC (Mothership) or a first stop at PSC (‘Drip ‘n Ship’) [35 (link)]. In this study accessibility has been modelled using the Mothership pattern.