Single Shock Followed by Immediate CPR
You should deliver ONE shock at a time during CPR for ventricular fibrillation or pulseless ventricular tachycardia, followed immediately by 2 minutes of uninterrupted chest compressions before checking the rhythm again. 1
Current Standard Protocol
The American Heart Association changed from 3 stacked shocks to a single-shock strategy in 2005, and this remains the current standard of care. 2, 3
The single-shock approach is reasonable for defibrillation (Class IIa recommendation). 1
Why Single Shocks Are Recommended
The rationale for this fundamental change is threefold:
- Modern biphasic defibrillators have very high first-shock success rates (>90%), making multiple stacked shocks unnecessary. 2, 4
- When VF is terminated, a brief period of asystole or pulseless electrical activity typically follows, meaning a perfusing rhythm is unlikely to be present immediately after the shock. 1
- Minimizing interruptions in chest compressions improves survival, as the myocardium requires oxygen and substrate delivery through compressions to make subsequent shocks more likely to succeed. 2, 3
Post-Shock Management
After delivering a shock, you must immediately resume CPR without checking the rhythm or pulse:
- Resume chest compressions immediately after the shock and continue for 2 minutes (approximately 5 cycles of 30:2 compressions to ventilations). 3, 1, 5
- Do not check the rhythm or pulse immediately after shock delivery, as the majority of patients remain pulseless for over 2 minutes post-shock, with mean time to return of spontaneous circulation being 280 seconds (median 136 seconds). 6
- Check the rhythm only after completing 2 minutes of CPR, then deliver another single shock if VF/pVT persists. 7, 1
Evidence Supporting This Approach
An RCT of 845 out-of-hospital cardiac arrest patients found no difference in 1-year survival when comparing single shocks with 2 minutes of CPR versus the previous protocol of 3 stacked shocks with 1 minute of CPR between shocks. 1
This change in 2005, coupled with emphasis on minimizing interruptions in chest compressions, was associated with significant increases in survival from prehospital cardiac arrest associated with VF or pulseless VT. 2
Energy Selection for Subsequent Shocks
If the first shock fails and VF/pVT persists after 2 minutes of CPR:
- For biphasic defibrillators: It is reasonable to use the same energy level (typically 150-200 J) for subsequent shocks, or you may consider escalating the energy if the device allows (Class IIa for fixed energy, Class IIb for escalating). 1
- For monophasic defibrillators: Use 360 J for all shocks. 5
Common Pitfall to Avoid
Never delay defibrillation to establish advanced airway or IV access when VF/pVT is present—the first shock must be given without delay. 4 However, once the first shock is delivered, immediately resume compressions rather than pausing to check the rhythm, as post-shock asystole typically lasts a mean of 69 seconds before any organized rhythm returns. 6