What is the initial shock dose in joules for cardiac arrest?

Initial Shock Energy for Cardiac Arrest

For ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT), use 120-200 J for the initial shock with a biphasic defibrillator, or 360 J if using a monophasic defibrillator. 1

Biphasic Defibrillators (Preferred)

Follow the manufacturer's recommended energy dose for your specific device, typically ranging from 120-200 J for the first shock. 1

• If the manufacturer's recommendation is unknown, use the maximum available energy on the device 1
• The American Heart Association 2020 guidelines explicitly state biphasic waveforms are preferred over monophasic 1
• Both biphasic truncated exponential (BTE) and rectilinear biphasic (RLB) waveforms demonstrate 85-98% effectiveness for first shock termination of VF 1

Device-Specific Considerations

• RLB waveforms typically deliver more energy than selected based on patient impedance, so a 120 J setting may actually deliver approximately 150 J 1
• Recent evidence from 2025 shows no significant difference in outcomes between initial doses when analyzed per kg of body weight, suggesting the range of 120-200 J is appropriate 2

Monophasic Defibrillators

Deliver 360 J for the initial shock and all subsequent shocks. 1

• Monophasic waveforms require higher energy than biphasic to achieve equivalent defibrillation success 1, 3
• The European Resuscitation Council historically recommended starting at 200 J for monophasic, but current consensus favors 360 J 1

Subsequent Shocks

For second and subsequent shocks, use at least the same energy as the first shock, with consideration for escalating to higher energy levels. 1

Escalating vs. Fixed Energy Strategy

• Either fixed or escalating energy strategies are acceptable based on manufacturer instructions 1
• Recent 2025 data from China suggests escalating energy (200-300-360 J) may be superior for establishing sustained organized rhythm in refractory VF, particularly after the third shock (35% vs 18% success, p=0.003) 4
• A 2017 study found first-shock termination rates were similar between low-energy (150 J) and escalating higher-energy protocols (66.67% vs 64.41%), but conversion rates increased substantially at 360 J (38.95%) 5

Practical Algorithm for Subsequent Shocks

1. If VF persists after first shock: Consider escalating to 300 J, then 360 J for biphasic devices 4
2. If VF recurs after successful termination: Use the previously successful energy level 1
3. For manual defibrillators capable of escalating energies: Higher energy for subsequent shocks is reasonable 1

Critical Timing Considerations

Minimize the interval between stopping chest compressions and delivering the shock—even a few seconds matters. 1

• Resume CPR immediately after shock delivery without checking pulse or rhythm 1
• Continue CPR for 2 minutes before the next rhythm check 1
• One provider should resume compressions while the second charges the defibrillator to minimize hands-off time 1

Common Pitfalls

• Do not deliver stacked shocks (multiple shocks in succession without CPR)—this practice was abandoned because biphasic waveforms have very high first-shock success rates 1
• Do not check pulse immediately after shock—resume compressions first 1
• Do not delay defibrillation to perform prolonged CPR unless EMS response time exceeds 4-5 minutes 1
• Impedance changes minimally between shocks (often <1%), so increasing current requires increasing energy settings, not relying on impedance reduction 6
• First-shock failure often predicts lower efficacy for subsequent shocks, with 5% of patients accounting for 71% of failed shocks 6