🚑 Cardiac Arrest Bystander CPR Guidance App

Bystander CPR, Dispatcher Guidance, and Early Defibrillation — The Science Behind Every Second

Out-of-hospital cardiac arrest (OHCA) kills faster than almost any other medical emergency: without intervention, survival falls by roughly 7–10% every minute. Yet OHCA is uniquely treatable in the field — bystanders equipped with nothing more than their hands, a phone, and a nearby AED can double a victim's odds of walking out of the hospital. This page summarizes the evidence base the simulator above is built on.

• ~8–10%: US OHCA survival to discharge (all-rhythm, EMS-treated arrests)
• 30–40%+: Witnessed shockable + bystander CPR/AED (survival to discharge)
• 7–10%/min: Survival decline without defibrillation (for VF / pulseless VT)
• ~30% → 40%+: US bystander CPR rate (historical vs. modern T-CPR era)

The Chain of Survival

The American Heart Association frames OHCA response as a Chain of Survival: (1) early recognition of arrest and activation of emergency response, (2) immediate high-quality bystander CPR, (3) rapid defibrillation, (4) advanced EMS/ACLS care, and (5) integrated post-arrest and rehabilitative care. Each link depends on the one before it — a fast 911 call is worthless without someone willing to start compressions, and flawless compressions cannot restart a fibrillating heart without a shock. The chain is only as strong as its weakest link, and in most communities that weak link is bystander action in the first few minutes before EMS arrives.

Roughly 90% of OHCAs occur at home or in public, and in the vast majority a bystander is present. Every minute that passes before compressions begin costs measurable survival — brain and myocardial ischemia compound quickly once circulation stops.

Dispatcher-assisted CPR (T-CPR / DA-CPR)

Telephone-CPR (T-CPR), also called dispatcher-assisted CPR, is the practice of a 911/999/112 dispatcher recognizing a probable cardiac arrest from the caller's description, then talking the bystander through chest compressions in real time — "push hard, push fast, right here on the center of the chest" — using a simplified compression-only protocol, often synced to a metronome or cadence count the dispatcher speaks aloud.

Multiple US and international studies have found that structured T-CPR protocols roughly double bystander CPR rates compared with communities without them, and are associated with meaningfully higher survival to discharge and better neurological outcomes. T-CPR works because it removes the single biggest barrier to bystander action: not knowing what to do, or freezing under panic. It also compresses the time-to-first-compression interval, which is one of the strongest predictors of survival in the literature.

Modern smartphone CPR-guidance apps extend the same idea outside the 911 call: visual/audio metronomes paced to 100–120/min, phone-accelerometer depth estimation, and step-by-step voice prompts give real-time feedback on rate and depth quality — precisely the feedback loop the "T-CPR / App Feedback" toggle in the simulator models.

Compression mechanics — rate, depth, and recoil

AHA/ILCOR guidelines specify a compression rate of 100–120 per minute and a depth of at least 5 cm but not more than 6 cm in an average adult, with full chest recoil allowed between compressions so the heart can passively refill. All three parameters matter independently:

• Too slow (<100/min): inadequate cardiac output and coronary flow between compressions. • Too fast (>120/min): compressions become shallow and incomplete because there isn't time for full recoil, and diastolic filling time shrinks. • Too shallow (<5 cm): insufficient intrathoracic pressure generation to produce forward flow. • Too deep (>6 cm): increases risk of rib fracture, sternal fracture, and cardiac/pulmonary injury without added hemodynamic benefit. • Incomplete recoil (leaning on the chest): raises intrathoracic pressure at rest, reducing venous return and coronary perfusion pressure — a subtle error that's invisible without feedback.

Chest Compression Fraction (CCF) — the percentage of resuscitation time that compressions are actually being delivered — is itself an outcome-linked metric; guidelines target CCF ≥ 60%, ideally > 80%. Every pause (rescue breaths, rhythm analysis, pulse checks) reduces coronary perfusion pressure, which takes many subsequent compressions to rebuild — this is why the simulator's 30:2 conventional mode visibly dips its CCF and CPP each time breaths are given.

Hands-only vs. conventional CPR

Compression-only ("hands-only") CPR is recommended by the AHA for untrained bystanders and lay rescuers responding to a witnessed adult collapse: it is easier to perform correctly under stress, avoids hesitation around mouth-to-mouth contact, and studies show outcomes at least as good as conventional CPR for witnessed adult arrests of presumed cardiac origin.

Conventional CPR with rescue breaths (30 compressions : 2 breaths) remains recommended for: rescuers trained in CPR who are confident performing breaths, pediatric arrests, and asphyxial/hypoxic arrests such as drowning, drug overdose, and choking — situations where the primary problem is oxygenation rather than a purely electrical cardiac event, so ventilation matters more.

The 30:2 ratio trades a small compression-time cost for oxygen delivery. In a witnessed adult VF arrest, blood already contains usable oxygen for the first several minutes — which is exactly why hands-only CPR performs so well for that specific scenario, while asphyxial arrests deplete oxygen content first and benefit more from breaths.

Early defibrillation and Public Access Defibrillation (PAD)

For the most common shockable rhythms in early OHCA — ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT) — defibrillation is the only intervention that reliably converts the rhythm. Survival for shockable OHCA falls by an estimated 7–10% for every minute that passes without a shock when no bystander CPR is being performed; high-quality bystander CPR slows, but does not stop, that decline by sustaining some coronary and cerebral perfusion until a shock is available.

Public Access Defibrillation (PAD) programs place AEDs in airports, gyms, offices, and other public venues specifically to shrink the time-to-first-shock below the ~8–12 minute typical EMS response interval in many regions. AEDs are designed for untrained laypeople: they analyze the rhythm automatically and only permit a shock when a shockable rhythm is detected, with voice prompts guiding pad placement and compressions between shocks.

Community first-responder apps (in the spirit of PulsePoint) extend PAD further: when a 911 center receives an OHCA call, the app simultaneously alerts nearby CPR-trained citizen volunteers and shows them the location of the nearest registered AED, so a volunteer can arrive with a defibrillator before EMS — directly shortening the time-to-shock interval that dominates survival odds.

Witnessed VF arrest with an AED shock delivered within the first few minutes, combined with high-quality bystander CPR, is associated with survival to discharge in the 30–40%+ range in published series — several times the ~8–10% baseline for all-rhythm, unwitnessed OHCA treated by EMS alone.