Modeling the impact of public access defibrillator range on public location cardiac arrest coverage

Abstract

Background: Public access defibrillation with automated external defibrillators (AEDs) can improve survival from out-of-hospital cardiac arrests (OHCA) occurring in public. Increasing the effective range of AEDs may improve coverage for public location OHCAs.

Objective: To quantify the relationship between AED effective range and public location cardiac arrest coverage.

Methods: This was a retrospective cohort study using the Resuscitation Outcomes Consortium Epistry database. We included all public-location, atraumatic, EMS-attended OHCAs in Toronto, Canada between December 16, 2005 and July 15, 2010. We ran a mathematical model for AED placement that maximizes coverage of historical public OHCAs given pre-specified values of AED effective range and the number of locations to place AEDs. Locations of all non-residential buildings were obtained from the City of Toronto and used as candidate sites for AED placement. Coverage was evaluated for range values from 10 to 300 m and number of AED locations from 10 to 200, both in increments of 10, for a total of 600 unique scenarios. Coverage from placing AEDs in all public buildings was also measured.

Results: There were 1310 public location OHCAs during the study period, with 25,851 non-residential buildings identified as candidate sites for AED placement. Cardiac arrest coverage increased with AED effective range, with improvements in coverage diminishing at higher ranges. For example, for a deployment of 200 AED locations, increasing effective range from 100 m to 200 m covered an additional 15% of cardiac arrests, whereas increasing range further from 200 m to 300 m covered an additional 10%. Placing an AED in each of the 25,851 public buildings resulted in coverage of 50% and 95% under assumed effective ranges of 50 m and 300 m, respectively.

Conclusion: Increasing AED effective range can improve cardiac arrest coverage. Mathematical models can help evaluate the potential impact of initiatives which increase AED range.

Figure 1

Inclusion/exclusion criteria for cardiac arrest episodes

Figure 2

Locations of included cardiac arrests from December 16, 2005 to July 15, 2010 (top) and candidate sites for AED placement (bottom)

Figure 3

Coverage potential from placing AEDs in all 25,851 candidate sites in Toronto and coverage potential of 50, 100, 150 and 200 optimal AED locations

Figure 4

Example model output showing historical cardiac arrests and optimal 100 AED locations for effective range of 100m

Figure 5

Combinations of total AEDs and effective range required to achieve constant coverage potentials between 5% and 50%; points A and B show 70 and 15 additional AEDs are needed to increase coverage from 15% to 20%, respectively