Drone Delivery of Automated External Defibrillators to Lay Users (DAEDALUS): A Proof of Concept Study

STUDY PROTOCOL: Drone Delivery of Automated External Defibrillators to Lay Users (DAEDALUS): A proof of concept study

1. BACKGROUND Out-of-hospital cardiac arrest (OHCA) is a medical emergency where the heart suddenly stops beating, causing a cessation of blood flow to vital organs. Many cardiac arrests are triggered by the heart entering an abnormal rhythm, known as an arrhythmia, which disrupts its ability to pump blood effectively. Defibrillation, the process of delivering an electric shock to the heart using an Automated External Defibrillator (AED), can correct this abnormal rhythm and restore normal heart function, significantly improving the chances of survival when administered promptly (1, 2). AEDs are designed to be simple to use, with prompts guiding untrained bystanders through applying the device and performing CPR. Quick access to an AED can increase the chances of survival by 50-70% (3), and each minute without defibrillation reduces survival rates by approximately 10%. In the UK, over 30,000 OHCAs occur each year, but survival rates remain below 10%, largely due to delays in administering defibrillation (4).

Public access AEDs are placed in busy public areas to assist bystanders during a cardiac arrest before ambulance services arrive, significantly increasing the chances of survival (5). However, their effectiveness is limited by the accessibility and speed at which they can be retrieved and used, particularly in residential areas where 80% of cardiac arrests occur (6). AED usage remains low (\<5%) because most cardiac arrests happen at home, where AEDs are rarely available (7). This highlights the critical need for solutions that can rapidly deliver AEDs to residential locations. Only 2% of out-of-hospital cardiac arrests (OHCAs) in residential settings result in successful resuscitation (8). The disparity in survival rates between public and private settings underscores the need for solutions to ensure AED deployment, including in residential areas. Only 48% of 999 calls for cardiac arrests meet the target response time of an ambulance arriving with an AED in 7 minutes (9). A new solution is therefore much needed, and this project is timely. 2. RATIONALE Drones offer a promising solution by enabling rapid AED delivery. However, while drone-based AED delivery systems have shown potential in other countries like Sweden, the UK has unique regulatory, logistical, and cultural factors that have yet to be explored or addressed.

Our study fills this gap by focusing specifically on integrating drones into the UK's emergency response system, accounting for UK airspace regulations, NHS ambulance service protocols, and public perception within the UK cultural context. This research aims to ensure that drone-delivered AEDs are integrated into real-world practice, ultimately improving the rate of defibrillation, decreasing the time to defibrillation and improving survival.

A key aspect of what sets our study apart from any previous study is the collaboration with the UK Civil Aviation Authority (CAA), Kent Surrey Sussex Air Ambulance (KSS), and Everdrone. The CAA is the UK's aviation regulator, responsible for providing oversight of all air traffic and drone operations within UK airspace, and importantly, we have CAA approval for this project. KSS, the air ambulance service for the region, will be the organisation running the drone service in this study, ensuring it is integrated with NHS emergency response systems. Everdrone, a Swedish company with extensive experience in medical drone technology, will pilot the drones and provide technical support.

Flying drones Beyond Visual Line of Sight (BVLOS)-where the drone operates outside the range that the operator can physically see-has been restricted. To overcome these challenges, there needs to be robust systems in place for detecting and avoiding obstacles, managing air traffic, and ensuring communication between the drone and the operator. Until these issues are fully resolved, the use of drones for regular operations, especially in complex airspace, has remained limited.

The CAA's BVLOS Sandbox is a controlled environment designed to address these challenges. It allows organisations to test the safety of BVLOS drone operations. By participating in the sandbox, KSS can trial drones in real-world scenarios under carefully monitored conditions, while the CAA gathers data to develop regulations that will eventually allow BVLOS operations to become a regular part of UK airspace. As indicated above, importantly, we have CAA approval for the use of BVLOS for this study, as part of the Sandbox.

KSS and Everdrone are key partners of Project LifeLine, a specific initiative within the BVLOS Sandbox that focuses on using drones for emergency medical deliveries, such as delivering Automated External Defibrillators (AEDs), EpiPens, and other life-saving equipment.

Our collaboration with KSS, Everdrone, and the CAA places this study at the forefront of medical drone technology, which has not been possible until this point. Everdrone has already successfully deployed AED drones in Sweden, showing that this technology can save lives. However, the UK's airspace is more complex, especially in urban areas like those near London Gatwick Airport. The CAA BVLOS Sandbox is crucial in helping us test and refine drone operations to ensure they are safe and well-integrated into the UK's regulated airspace. This study will generate the data needed to help pave the way for BVLOS drone operations to become a routine part of emergency medical services and help generate CAA approval beyond the CAA Sandbox.

Everdrone's system has already been assessed by the CAA as effective and safe, with a pilot project scheduled by KSS to start in late 2025. The aim of our study is to ensure that the integration and protocols developed through our work will optimise drone operations for this pilot. If our study does not go ahead, the scheduled pilot may proceed without the benefit of refined, UK-specific protocols, potentially limiting its effectiveness. 3. RESEARCH QUESTION/AIM(S)

The main research questions for this study are:

1. What are the communication, operational, and logistical challenges of using drones to deliver Automated External Defibrillators (AEDs) as part of the UK 999 emergency response system? 2. What are the public perceptions and acceptability challenges associated with the use of drones for delivering AEDs in emergency situations?

The overarching aim of the DAEDALUS study is to conduct a proof-of-concept study to develop, test and refine an integrated system to enable

3.1 Objectives

The study has the following objectives:

i. Iteratively developing and testing protocols for the integration of drone-delivered AEDs into the 999-emergency response system ii. Evaluating public and responder perceptions, including barriers and acceptability, to ensure lay responders can effectively use drone-delivered AEDs.

iii. Identifying and addressing operational challenges to ensure AEDs are deployed and applied quickly.

3.2 Outcome The primary output of this research will be tested protocols for drone-based AED delivery in the UK. These protocols will be adaptable for other emergency medical equipment, such as stop the bleed kits, medications, and blood products. We will publish all findings in open-access formats, ensuring wide dissemination to support other Air Ambulance and NHS services in augmenting healthcare logistics. This project will also help inform future medical drone initiatives, improving the delivery of life-saving devices across the country.

4 STUDY DESIGN and METHODS of DATA COLLECTION AND DATA ANALYSIS This mixed-methods study uses a concurrent triangulation design to gather complementary quantitative and qualitative data (22). The study is divided into two work packages (WP): WP1 involves developing an integrated system for drone-delivered AEDs and testing this system through simulated trials. WP1 is split into two phases: protocol development and simulation trials to refine the system. WP2 is a qualitative interview study with individuals who have lived experience of OHCA or their family/carers, as well as members of the public with no experience of OHCA. Both WPs will run concurrently, with findings from each informing the other through a continuous feedback mechanism, enhancing the overall study design and implementation (see section on integration of WP1 and WP2).

The flowchart presented in Figure 1 illustrates an example of the end-to-end process of drone-delivered AEDs as part of the UK's emergency medical response system, and the focus of our study in designing robust and tested protocols for this pathway.

Figure 1 End-to-End Process Flow of Drone-Delivered AED Integration into the UK Emergency Response System

WP 1 Phase 1 - Development stage A key challenge in drone-delivered medical devices is integrating 999 callers, ambulance dispatch, ATC, and drone operators into a rapid, coordinated system. Phase 1 focuses on creating and refining protocols for seamless drone use. Clear communication is essential, ensuring the caller knows exactly where the AED is delivered (e.g., "on the back door mat") to minimise any time without CPR, especially if only one lay responder is present.

To develop this, experts, public contributors, the research team, Everdrone, SECAmb, ATC, and KSS-will collaborate to map out the process, design the communication pathway, and establish criteria for AED drone deployment. The current plan involves the HEMS dispatcher in SECAmb's Emergency Operations Centre auto-allocating drones to Category 1 incidents (e.g., presumed cardiac arrest) to prioritise early defibrillation and improve survival outcomes.

Monthly online meetings over four months will guide the protocol development (see Gantt chart). Between meetings, the research team will refine protocols based on discussions. Findings from WP2-gathering public and responder perceptions-will inform the ongoing development.

Phase 2 - Simulation process

In this simulation, we replicate a real-world out-of-hospital cardiac arrest (OHCA) scenario as follows:

i. A lay responder, positioned with a medical training manikin representing a patient experiencing OHCA at Redhill Aerodrome, begins the scenario by placing a simulated 999 call. This call reaches the study Emergency Medical Advisor (EMA) (999 call handler) stationed at SECAmb's Emergency Operations Centre (EOC).

ii. The EMA triages the 999-call using the NHS Pathways system (https://digital.nhs.uk/services/nhs-pathways) (as per standard protocol within SECAmb), determining the patient is in cardiac arrest. The lay responder is guided through basic life support instructions, mirroring real-life emergency response protocols for OHCA.

iii. Simultaneously, a Helicopter Emergency Medical Service (HEMS) (air ambulance) dispatcher, using the computer-aided dispatch system (CAD), assesses the incident based on pre-established criteria from Phase 1. If the scenario meets the criteria for drone-delivered AED intervention, the dispatcher initiates the deployment process.

iv. Upon receiving the dispatcher's signal, an Everdrone pilot in Sweden, connected through a real-time web communication link, prepares for launch. A local ground pilot is stationed at Redhill Aerodrome, in accordance with CAA regulations requiring a visual line of sight for drone operations. The Everdrone pilot launches the AED-equipped drone from the Skybase (drone hangar) at the KSS base, aiming for a launch time of less than 90 seconds from the initial 999 call.

v.: The drone is navigated to the simulation site, where it uses a winch and spool system to lower the AED to the lay responder's location. The HEMS dispatcher, observing via the drone's video link, communicates with the EMA through the CAD system to precisely direct the lay responder to the AED's drop point.

vi. The EMA instructs the lay

• Research publications [Time frame: From enrolment to submitting research papers to publications in Spring 2027]