Potential effects of a mobile stroke unit on time to treatment and outcome in patients treated with thrombectomy or thrombolysis: A Danish-German cross-border analysis

Abstract

Background and purpose: A mobile stroke unit (MSU) reduces delays in stroke treatment by allowing thrombolysis on board and avoiding secondary transports. Due to the beneficial effect in comparison to conventional emergency medical services, current guidelines recommend regional evaluation of MSU implementation.

Methods: In a descriptive study, current pathways of patients requiring a secondary transport for mechanical thrombectomy were reconstructed from individual patient records within a Danish (n = 122) and an adjacent German region (n = 80). Relevant timestamps included arrival times (on site, primary hospital, thrombectomy centre) as well as the initiation of acute therapy. An optimal MSU location for each region was determined. The resulting time saving was translated into averted disability-adjusted life years (DALYs).

Results: For each region, the optimal MSU location required a median driving time of 35 min to a stroke patient. Time savings in the German region (median [Q1; Q3]) were 7 min (-15; 31) for thrombolysis and 35 min (15; 61) for thrombectomy. In the Danish region, the corresponding time savings were 20 min (8; 30) and 43 min (25; 66). Assuming 28 thrombectomy cases and 52 thrombolysis cases this would translate to 9.4 averted DALYs per year justifying an annual net MSU budget of $0.8M purchasing power parity dollars (PPP-$) in the German region. In the Danish region, the MSU would avert 17.7 DALYs, justifying an annual net budget of PPP-$1.7M.

Conclusion: The effects of an MSU can be calculated from individual patient pathways and reflect differences in the hospital infrastructure between Denmark and Germany.

Keywords: drip and ship model; mobile stroke unit; stroke; thrombectomy; thrombolysis.

FIGURE 1

Mapping of patient pathways. The two study regions are located adjacent to each other on the two sides of the Fehmarn Belt (a). Hospital landscapes and patient locations are displayed for the German region (b) and the Danish region (c), both inhabited by about 500,000 people. Blue points denote individual locations of stroke patients who have been treated in the thrombectomy centre of the University of Lübeck (triangle in left map) and in the thrombectomy centre of the University of Copenhagen (triangle in right map). Plus symbols show the positions of the seven primary hospitals in Germany and the single primary hospital in Denmark. Patients were admitted to a primary hospital first. After initial imaging and thrombolysis (if applicable) they were brought to the thrombectomy centre with a secondary transport. This real‐world situation was compared to a hypothetical MSU pathway that starts thrombolysis at the patient location and admits them directly to the thrombectomy centre, bypassing the primary hospital. The red ambulance symbol denotes the optimized MSU location rendered by AI using the Nelder–Mead algorithm.

FIGURE 2

Flowchart displaying inclusion and exclusion of patients in the two cohorts.

FIGURE 3

Timeline from the 112 call to groin puncture (see also Table 1).

FIGURE 4

Prognostication of annual DALYs averted by MSU implementation is colour‐coded for different combinations of thrombectomy cases (y‐axis) and thrombolysis cases (x‐axis) for the German region (a) and the Danish region (b). Note the overall smaller effect in the German region that is mainly dependent on thrombectomy cases, reflecting the minor time saving for thrombolysis cases. Plotted as dashed lines are isolines of averted DALYs multiplied by society‐adapted granted cost per DALYs averted (Germany PPP‐$84.506; Denmark PPP‐$94.390) in $0.5M steps. These lines reflect the maximal annual net cost of an MSU that would justify its effect in the eyes of society. Black circles denote the assumption that the MSU reaches 40% of 130 thrombolysis cases and 40% of 70 thrombectomy cases within each region. This allows for an annual MSU budget of $0.8M in the German region (black circle in (a)). After two new thrombectomy centres in the German region were established recently, the net annual MSU budget shrinks to below $0.5M (light grey circle in (a)) due to the low number of remaining thrombectomy cases. The net annual MSU budget justifying its benefits in the Danish region amounts to $1.7M (black circle in (b)), due to the large influence on both thrombolysis and thrombectomy cases, with an unchanged hospital landscape restricted to one primary hospital and one thrombectomy centre.