Aeromedical Retrieval for Stroke in Australia

Date published

02 Jul 2020

Stroke is a massive global health challenge. With 13.5 million new strokes each year and 5.5 million deaths, stroke is a leading cause of mortality and chronic disability. The most effective intervention for acute stroke, apart from thrombolysis or endovascular clot retrieval, is management in a specialised stroke unit. Importantly, the majority of these reperfusion therapies are best administered within 4.5 h of stroke onset. Times beyond this, sometimes up to 24 h, may only be considered when more sophisticated imaging techniques are applied to detect the presence of viable brain tissue, the ischaemic penumbra. Most Australians living in rural and remote areas do not have access to SUs, with the majority required to travel more than 200 km by road to access medical care. As such, many patients living in rural and remote areas require aeromedical retrieval by the Royal Flying Doctor Service.

However, it is unclear how many stroke patients undergo RFDS aeromedical retrievals, from remote and very remote Australia, to inner regional areas and major city hospitals. Their demographic characteristics and stroke subtypes are also unknown. Furthermore, the time sequence of events from stroke onset to eventual arrival at a healthcare facility capable of diagnosis and treatment is unclear.

Hence, the RFDS research team aimed to provide the first information on the characteristics of patients, who underwent an RFDS aeromedical retrieval for stroke during a set period throughout Australia. We aimed to estimate the times between first notification and arrival to the treating hospital airstrip and to test the hypothesis that receiving and transfer locations have different SU and imaging capability.

We have provided the first information on the retrievals by air for patients with a diagnosis of stroke in Australia. There were several important findings, which may have implications for future healthcare planning. First, the absolute numbers of patients were high at 1,773, a somewhat greater proportion being males and representing 1.7% of air retrievals during this period. Second, the proportion of patients who were Indigenous was high at 16.5%, significantly greater than the average for Australia as a whole (3.0%). Indigenous patients were also much younger. Third, the majority of patients did not have a specific diagnostic subtype of stroke established, particularly intracranial haemorrhage versus infarction, thus making early therapeutic intervention impossible. Fourth, time delays of transfer were such that even in cases where a specific diagnosis was made, the therapeutic time windows were beyond those for standard thrombolysis without more sophisticated imaging assessment. Finally, many of the transfers were made to centres with designated SUs and appropriate imaging facilities.

The median age of our cohort was 62.7 years. The younger age of Indigenous patients compared with non-Indigenous patients is striking and consistent with other Australian hospital-based studies. For example, a recent study of stroke patients seen at the Royal Adelaide Hospital found that the average age was much lower in Aboriginal than in non-Aboriginal people (51 vs. 78 years, p < 0.001) and that the age-standardised stroke incidence per 100,000 in Aboriginal people was nearly double that in non-Aboriginal people (p < 0.001) [12]. The cause of this disparity is unclear; however, it may in part be linked to the higher rates of cardiovascular risk factors, coupled with discrimination and disadvantage (including economic, environmental, and educational), institutional racism, communication barriers and the lack of culturally appropriate services, and transportation to health centres in rural and remote Australia [13].

The estimated median time from first notification to patient arrival at hospital was 238 min (4 h). These figures are higher than the Australia metropolitan average of 150 min [14], and services using the Prehospital Acute Stroke Triage (PAST) protocol of 90.5 min from symptom onset to emergency department arrival [15]. As mentioned, the majority of aeromedical retrievals came from remote areas without SU availability, with the majority being transferred to hospitals with SUs.

The RFDS median overall transfer time of 238 min is also higher than what has been reported in other countries. A study from the Polish Medical Air Rescue found that the median time from activation to stroke patient transfer was 60 min [16]. Furthermore, a study from the Norwegian Air Ambulance Service indicated that it took 19 min flying time on average to reach PE patients [17]. However, the median flight time from mobilisation to scene (i.e., flight time to patient) by the RFDS was 58 min (as detailed in Fig. 2), which is similar to the Polish Medical Air Rescue transfer times. The longer median overall transfer time of the RFDS is most likely due to the significant longer distances the RFDS required to travel, due to the vastness of Australia, compared to other national retrieval services [7]. Fortunately, a prospective study is planned, in which response times among the leading aeromedical services of the world will be compared.

A precise stroke diagnosis is required to enable treatment. Without knowing the stroke type, ischaemic or haemorrhagic, through diagnostic imaging, acute reperfusion therapy cannot be instituted. Ischaemic strokes, caused by arteries being blocked or narrowed, require treatment to restore adequate blood flow to the brain, most often via intravenous tPA. Even more dramatic benefits are seen with endovascular thrombectomy for patients with large artery occlusion [1318]. Whereas haemorrhagic stroke, caused by extravasation of blood into the brain, requires measures to control the bleeding and reduce pressure in the brain [118]. However, this study demonstrated that the majority of aeromedical retrieval sites did not have access to diagnostic imaging, thus limiting stroke subtype diagnosis, immediate inflight treatment, and redirection to an appropriate comprehensive stroke centre.

The establishment of traditional SUs in rural and especially remote areas is not feasible due to sparse population distribution over vast areas. The greatest benefits in stroke intervention are achieved very early after onset, particularly in the first “golden hour” [19]. However, a major and persistent issue with the treatment of stroke in remote Australia is the vast geographical distance required to travel to access emergency care, significantly limiting intervention in the most critical time window [8]. As mentioned, we found that the majority of the remote population do not have access to radiology/imaging within 60 min drive time and that diagnostic imaging was not available for many of the aeromedical retrievals. This is consistent with an Australian report that found that patients living in rural and remote areas have “limited access to appropriate diagnostic imaging services; and patients face additional costs to access those services” [20]. This, coupled with remote emergency responders having limited access to up-to-date imaging facilities and specialist support, makes an appropriate diagnosis difficult [21].

This study needs to be put in the context of the revolution that has occurred in acute stroke therapies over the last few decades. Reperfusion therapies, in particular, have the potential to improve outcomes dramatically when administered early after the stroke onset. Means of delivering earlier prehospital therapies are emerging, for example, recent trials of prehospital models of early intervention with mobile stroke units (MSUs) have been implemented in Australia [1322]. To date, these have been confined to metropolitan areas with high population density. These MSUs are specialised ambulances with on-board CT and point-of-care pathology tools with the potential for telemedicine connection to a stroke specialist. Early studies show that more patients can be treated with tPA and the time to treatment can be reduced by over 40 min [14192324]. Of interest, a Norwegian MSU in a similar rural setting has been able to provide stroke patients with thrombolysis within 60 min after the symptom onset. Similar to RFDS aeromedical retrievals, this service included an emergency physician [25]. How this emerging pre-hospital paradigm might be adapted to include an Australian rural and remote service provider or population needs to be addressed.

The RFDS already provides extensive aeromedical retrieval support to remote populations, and as such, there is a great potential for the RFDS to develop and equip an aircraft(s) to become an MSU [24]. Walter et al. [24] proposed that RFDS aircrafts, in addition to current medical equipment, could carry a specially designed CT scanner. However, there are two main issues with this proposal, including the weight of the CT machine and the optimal location of a single RFDS MSU. The issue of distances and the vast distribution of RFDS stroke patients make the provision of only a limited number of aeromedical MSUs impractical. An innovative and more expansive solution is needed.

For example, the potential of ultra-lightweight and low-cost brain imaging devices needs to be explored. For an RFDS patient receiving an aeromedical transfer for a stroke to a metropolitan hospital with an SU, the provision of a lightweight CT on the aircraft would potentially allow earlier stroke diagnosis and thrombolysis prior to transit. In addition to the RFDS, a lightweight and portable CT device could be deployed in several clinical settings, such as regional hospitals and road-based ambulance services, to make early stroke treatment a reality, independent of geographical location. To optimise the prehospital treatment of stroke, it is proposed that a transformative research program to develop, test, and implement novel disruptive technologies should be implemented.

This study was limited to RFDS patient data, and as such, it did not include other rural and remote healthcare providers. While all diagnoses were collected, a potential limitation is the accuracy of the recorded working diagnosis made in flight. However, it should be noted that this process is currently considered the gold standard in aeromedical medicine [49]. A further limitation was that we were unable to collect data from the time of onset of stroke symptoms to the transfer request. This limitation will be addressed in future studies, where all data will be prospectively accrued.

Citation: Gardiner F, W, Bishop L, Dos Santos A, Sharma P, Easton D, Quinlan F, Churilov L, Schwarz M, Walter S, Fassbender K, Davis S, M, Donnan G, A: Aeromedical Retrieval for Stroke in Australia. Cerebrovasc Dis 2020;49:334-340. doi: 10.1159/000508578