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Zhao et al. Vessel Plus 2021;5:10 I http://dx.doi.org/10.20517/2574-1209.2020.77 Page 9 of 12

Dispatch specificity
Dispatch accuracy is a current issue for Melbourne MSU operation. In our region, the currently used
emergency dispatch algorithm only has a 32% concordance with a paramedic diagnosis of stroke or TIA.
Not surprisingly, the Melbourne MSU is cancelled by either the first responding paramedic crew or by the
MSU personnel in 60% of cases, mainly due to low likelihood of stroke. This is normally while the vehicle
is en route to a case or, in some instances, after the MSU has physically arrived at the address.

This low specificity for stroke is particularly problematic for a single resource like the MSU, as the service
cannot attend concurrent dispatches or may be much further away from subsequent dispatched cases. The
Melbourne MSU is only attached to 65% of all potential dispatches in the 20-kilometre dispatch zone and
therefore cannot attend all stroke cases within the central operating area. Poor dispatch specificity worsens
this situation further if the vehicle is continually dispatched to low likelihood cases, further limiting the
availability of the MSU to attend patients who are eligible to receive pre-hospital stroke treatments.

The Berlin MSU group developed a new local dispatch algorithm derived from the most specific stroke
[41]
symptoms after retrospective analysis of emergency calls . This was prospectively evaluated for 274
patients in a 2-month trial after an 1 h training session with a small group of dispatchers, with the finding
[41]
of a positive predictive value of 47.8% for eventual diagnosis of stroke . Whilst initially promising,
no further validation has been conducted with a broader group of dispatcher personnel over a longer
timeframe. In the local Australian setting, there are also practical issues in whether the emergency dispatch
organizations are willing to use a bespoke algorithm for a single condition.

Future research in this area must address stroke dispatch in a whole systems approach, both for MSU
and regular ambulance dispatch. A multi-tiered approach is required, including consensus for changes to
internationally used emergency algorithms, review of local dispatch practices, training of emergency call
takers and development of dispatch screening procedures used by each MSU service. This optimization is
critical to allow best utilization of the limited number of MSUs worldwide and ensure these high-resource
services are cost-effective.

Functional outcomes
MSUs around the world have consistently demonstrated substantial time savings in commencement of
thrombolysis, with evidence for EVT time saving also shown by the Melbourne service. In almost all
instances this has led to clear benefits in functional outcomes in published literature [23,26] . Two major
clinical trials to determine the clinical efficacy of MSUs, based in the US and Germany (Clinicaltrials.gov
registrations: BEST-MSU trial NCT02190500 and B_PROUD trial NCT02869386) have recently completed
and full results are pending. These utilize pseudo-randomized methods of alternating MSU availability or
alternating dispatch regions. These results will be pivotal in future acceptance of MSUs as a gold standard
for clinical care, but the translatability of such results to the operational situation in Melbourne needs to
be carefully analyzed. Given that the Melbourne MSU shows greater time savings than some international
[2]
services and is able to provide EVT triage that is not possible in other regions, the potential benefit of the
Melbourne service may be greater than benefits reported in the trials.

Outside of clinical trials, the Berlin MSU group has conducted an interim observational analysis of the
effect of MSU operation on functional outcomes compared to in-hospital controls . When comparing 305
[10]
MSU thrombolysis cases to 353 control cases, there was a median time saving of 30 min (48 min vs. 76 min, P <
[10]
0.0005) for time from ambulance dispatch to commencement of thrombolysis in favor of MSU treatment .
Overall functional outcomes showed that there was a trend towards but no statistically significant benefit on
[10]
the prespecified primary endpoint of excellent outcome (modified Rankin Scale 0-1, 53% vs. 47%, P = 0.14) .