Community First Responder Routing Algorithm

Dispatch & Candidate Sets

• Build 10-min driving-distance isochrones around the patient: If ambulance inside continue with finding CFRs
• Build 10-min walking-distance isochrones around the patient; CFRs inside are alert-eligible. AEDs inside the patient isochrone are pickup-eligible. A CFR may fetch an AED only if located inside both isochrones.
• Account for availability: each CFR has a decline probability (≈76% day, 64% evening, 88% night); only accepters remain as candidates.
• From accepters, take the 100 or 150 closest (straight-line) CFRs as the final pool. Exactly one is sent direct to start CPR and one is sent via AED.

Objective (Survival Function)

• Survival (until first defibrillation possible) is modeled as P = 0.9^t_CFR · 0.97^t_CPR, where t_CFR is time from cardiac arrest to start of CPR and t_CPR is CPR duration before defibrillation.
• Defibrillation time is the earliest of: (i) CFR arriving with AED, or (ii) ambulance (“vector”) arriving with AED.

Assignment Logic

• If the fastest direct CFR and fastest via-AED CFR are different, use them as is.
• If the same CFR is fastest for both roles, compare three scenarios and pick the one with the highest P:
  1. Fastest goes direct, 2nd fastest fetches AED.
  2. Fastest fetches AED, 2nd fastest goes direct.
  3. Fastest alone fetches AED (if optimal).
• Walking speeds approximate brisk walking (not running) to reflect building exit/navigation and to avoid degrading CPR quality.
• Each scenario is simulated multiple times to reduce randomness from CFR placement.

Noted Limitation & Fix

• When modeling AEDs as 24/7 accessible, survival sometimes declines because the optimizer may favor AED detours even when an ambulance is due quickly. The fix is to incorporate the ambulance ETA directly into the assignment objective (or penalize AED detours when ambulance arrival is imminent).

Results

• Increase in survival rate flattens out around 1% CFRs.
• Highest survival rate at 8pm > 8am > 2pm > 2am.
• More CFRs arrive faster during the evening CFRs are in the residential neighbourhood Low decline rate.
• Prioritize direct routing to the Patient.