Analysis of aeromedical retrieval coverage using elliptical isochrones

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To the Editor:
We would like to thank the authors of the paper which provides impressive exposition of a novel flight isochrone modelling tool to estimate the impact of a proposed redesign for Scottish aeromedical resources.1
Some of the foundation statements justifying the study methodology and final conclusions drawn within the article we believe merit closer examination.
“The Inverness helicopter (“Helimed 2” [HM2]) is based at a large regional facility that will, however, not become a major trauma center, because it does not have the required specialties on site.”
Potentially important clarification and context to this statement:
“Since only Aberdeen would be able to provide sufficient numbers of doctors for a physician—staffed aircraft, we assumed that an additional aircraft (HMa) would be based in this location.”
This is an unreferenced and unqualified statement and given it justifies the entire methodology of the study merits close examination:
“The current helicopter network configuration provides 94.2% population coverage and 59.0% area coverage. The addition of a fourth helicopter would marginally increase population coverage to 94.4%, and area coverage to 59.1%. However, when considering only physician-manned aircraft, the current configuration provides only 71.7% population coverage and 29.4% area coverage, which would be increased to 91.1% and 51.2%, respectively, with a second aircraft.”
There is already 94.2% coverage of the population with existing air assets, but to obtain increased physician coverage, the solution proposed is to commission an extra helicopter where physicians are based, at significant expense, rather than take physicians to where existing helicopters in Inverness or Perth (and potentially their neighboring and far more capable SAR aircraft) are already paid for and established.
Both the area coverage and population coverage figures that are expressed here, using the flight isochrone ellipses do not appear to have been contextualized with factors crucial to retrieval services in the North of Scotland such as weather systems, topography or refuelling. These elements are relevant and regular predictors of journey time, delay and prevention. Failing to account for these, is of note to those engaged in retrieval service planning in nonurban areas of Scotland where these are daily concerns.3,4
“In contrast, from the perspective of the rare but unfortunate individual who is injured in a remote location, population coverage is irrelevant, and area coverage is more important. It is therefore important to consider both types of analyses. Maps depicting area coverage alone may be misleading.”
We appreciate how difficult it can be to summarize accurately the scale and frequency of actual major trauma and illness in the Highlands and Islands of Scotland, particularly as formal trauma audit data is collected in only one of the hospitals in that entire region. After the logic established in more mature trauma systems (and echoed within the Geospatial Evaluation of Systems of Trauma Care for Scotland study aforementioned), to achieve any of the mortality/morbidity benefits of a modern trauma system, health services must either achieve large scale throughput of patients into a single specialized centre, or improve the functionality of their networks.2,5 With a small national population spread over the proposed trauma network model of four MTCs, Scotland therefore relies on better patient retrieval and more effective primary treatment to benefit the population living in the more remote areas of Scotland.
Placing a helicopter next to a hospital in a densely populated urban area that would be better served by a physician staffed car response risks missing out on serving these patients for another generation. In the more urban areas of Scotland, it has been shown that retrieval of major trauma by road using fast-response vehicles is a more effective intervention.
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