Automated external defibrillator-equipped drones for facilitating early defibrillation in out-of-hospital cardiac arrest

Abstract

Background: Each year, approximately 3.8 million out-of-hospital cardiac arrests (OHCAs) occur globally. Survival rates are low (8–12%) and have not increased during the past decade. It is known that early cardiopulmonary resuscitation (CPR) and defibrillation increase the chance of survival in this patient group, and if given within the first three to five minutes, the chance of survival can be as high as 50– 70%. Unfortunately, the time taken for emergency medical services (EMS) to arrive is increasing in many countries. The number of publicly available automated external defibrillators (AEDs) has increased in recent years, but they are very seldom used. A reason for this could be that most public AEDs are placed in public locations, whereas approximately 70% of all OHCAs occur in residential locations. A promising novel method for delivering AEDs to the location of an OHCA is the use of AED-equipped drones, and previous studies have shown that AED-equipped drones have the theoretical potential to decrease the time to AED arrival and their use compared with standard procedures. Studies showing real-life feasibility, however, are missing. The overall aim of the current work and the included studies was to investigate, describe and evaluate how AED-equipped drones may facilitate early defibrillation in cases of OHCA.

Specific aims and methods: Study I was a registry-based retrospective study. Data were obtained from the Swedish registry for cardiopulmonary resuscitation (2010–2018) and analysed using a geographical information system (GIS). The aim was to identify areas in Sweden with a high incidence of OHCA and prolonged ambulance response times (> eight minutes), to identify optimal locations for placing AED-equipped drones. Study II was a feasibility study aiming to investigate if it is feasible to deliver AEDs using drones to patients with suspected OHCA. This was a prospective interventional study where three AED-equipped drones were dispatched and deployed in cases of suspected OHCA in western Sweden during a 4-month study period in 2020. Study III was a prospective interventional study with the aim of evaluating if AED-drones could deliver AEDs before ambulance arrival in cases of suspected OHCA. AED-drones were dispatched to cases of suspected OHCA in western Sweden over a study period of 11 months (2021–2022), and up to five AED-drones were active over the study period. Times for AED-delivery by drones were compared with ambulance response times. Study IV was an observational study including data from drone flights with AED-deliveries before EMS arrival in cases of suspected OHCA in Sweden between 2020 and 2023. The aim was to evaluate the characteristics and changes over time of dispatcher referral rate of bystanders to retrieve drone-delivered AEDs in cases of suspected OHCA. Based on experiences from Studies II and III, a bundle of interventional directives aimed to support dispatcher referral to AEDs was implemented at the dispatch centre in 2022. Emergency calls were then audited and evaluated using a case report form (CRF) based on a modified version of the Cardiac Arrest Registry to Enhance Survival (CARES).

Results: In Study I it was found that by using only relatively few AED-equipped drones, the proportion of historical OHCA cases that could have received an AED on scene within eight minutes increased substantially. By using 61 AED-equipped drones, all high-incidence areas (>100 OHCAs in 2010–2018) would have been covered (all patients would have received an AED within eight minutes, either by ambulance or drone), resulting in a coverage of 58.2%. Moreover, the study revealed that to increase the proportion of coverage, the number of AED-drones needed to be increased rapidly; for example, if going from 80% to 100% coverage, the number of drones had to increase from 366 to 2408. In Study II it was found that it is possible to implement AED-drones in the dispatch and EMS system and that it is feasible to deliver AEDs by using drones (11/12 cases; 92%). There was also a trend indicating that drones arrived prior to ambulance arrival in the majority of cases (7/11; 64%) with a median time benefit of 01:52 (min:sec, interquartile range (IQR) 01:35–04:54) compared with ambulance response times. Results from Study III showed that dispatch of AED-drones was possible in both daylight and darkness, during summer and winter. The drones delivered AEDs before ambulance arrival in 37 out of 55 cases (67%). In cases where the drone arrived first, a median time benefit of 03:14 (IQR 01:42–05:42) was seen. Moreover, drone-delivered AEDs were attached in 6/18 (33%) true OHCA cases and used to defibrillate two patients. One of these patients survived to 30 days. In Study IV, a total of 99 cases of AED-delivery using drones to suspected OHCAs before EMS arrival were included. Of these, dispatcher-referral of callers occurred in 25 cases (25%). Referral in confirmed EMS-treated OHCAs occurred in 21/37 cases (57%). The AED-referral rate in cases of confirmed EMS-treated OHCAs rose from 7/18 (39%) before bundle implementation (June 2020–May 2022) to 14/19 (74%) after bundle implementation (June 2022–May 2023). Of the EMS-treated OHCAs, 16/37 (43%) AEDs were attached, and 4/37 (11%) of the cases were defibrillated. The most common reasons for non-referral in EMS-treated OHCA were single bystander, distraught/unwilling caller and call ended early. The median time benefit for drones compared with the EMS was greater in the group of referred cases (03:00 vs. 01:54).

Conclusion: Altogether, the studies in this thesis show that it is feasible to implement AED-equipped drones in the chain of survival as part of the emergency medical response in cases of suspected OHCA. Drones can be deployed and deliver AEDs in the proximity of real-life cases of suspected OHCA in an automated fashion in various conditions (summer and winter, in daylight and in darkness). By using this novel method, an important time benefit compared with the standard EMS response can be introduced, and this significant time benefit creates a time window that makes the use of AEDs possible in cases of OHCA. Nevertheless, the clinical effect of the early AED-delivery is dependent on knowledge of CPR in the community, and the performance of dispatch centres during dispatcher-assisted cardiopulmonary resuscitation (DA-CPR). The AED-drone systems can be further optimized regarding performance, such as by introducing drones that can fly faster, have a longer range, and can fly in rougher conditions. Additionally, human factors, such as communication between dispatchers and laypersons/callers, could be improved so that more drone-delivered AEDs are used by laypersons during the first minutes of an OHCA.