What is the maximum dose of synchronized defibrillation for an adult patient in cardiac emergency?

Maximum Dose of Synchronized Cardioversion

The maximum dose for synchronized cardioversion in adults is 200 J for biphasic waveforms, though synchronized cardioversion should never be used for ventricular fibrillation or pulseless ventricular tachycardia—these require unsynchronized defibrillation at maximum available energy (typically 360 J for monophasic or 200 J for biphasic). 1, 2

Critical Distinction: Synchronized vs Unsynchronized Shocks

The term "synchronized defibrillation" requires immediate clarification because it represents a fundamental safety issue:

• Synchronized cardioversion is used only for organized rhythms with a pulse (stable or unstable VT with pulse, atrial fibrillation, atrial flutter, SVT) 2
• Unsynchronized defibrillation is used for pulseless rhythms (VF, pulseless VT) 1, 2

Never use synchronized mode for VF or pulseless VT—the device may fail to sense a QRS complex and deliver no shock at all, wasting critical seconds during cardiac arrest. 2

Maximum Energy Doses by Clinical Scenario

For Unstable Monomorphic VT With a Pulse (Synchronized)

• Initial dose: 100 J (biphasic or monophasic) 1, 2
• Subsequent doses: Escalate stepwise if initial shock fails 1, 2
• Maximum practical dose: 200 J for biphasic waveforms 1

For VF or Pulseless VT (Unsynchronized Defibrillation)

• Biphasic waveforms: 120-200 J initially (manufacturer-specific), with maximum dose available for subsequent shocks 1
• Monophasic waveforms: 360 J for all shocks 1
• If manufacturer's dose unknown: Use maximal dose available 1

For Polymorphic VT (Unsynchronized)

• Treat as VF with unsynchronized high-energy shocks—never use synchronized mode even if pulse present 2
• Use same energy doses as VF (120-200 J biphasic or 360 J monophasic) 1

Energy Escalation Protocol

For subsequent shocks in refractory VF/pulseless VT, energy should be at least equivalent to the first shock, and higher energy levels should be considered if the defibrillator is capable. 1

Recent evidence shows:

• Escalating energy regimens (200-300-360 J) demonstrate superior sustained VF termination compared to fixed lower-energy protocols for refractory rhythms requiring multiple shocks 3, 4
• First shock success rates are similar between fixed and escalating protocols (86-93% termination), but escalating energy improves outcomes for second and subsequent shocks 3, 5, 4
• The 2015 AHA guidelines acknowledge this evidence, recommending equivalent or higher energy for subsequent attempts 1

Common Pitfalls to Avoid

Never delay shock delivery to switch between synchronized and unsynchronized modes during cardiac arrest—pulseless rhythms always require immediate unsynchronized defibrillation 1, 2

Never use synchronized cardioversion for:

• Ventricular fibrillation (device cannot sense QRS) 2
• Pulseless ventricular tachycardia (delays treatment of cardiac arrest) 2
• Polymorphic VT even with pulse (synchronization usually impossible) 2

For biphasic defibrillators, the "maximum dose" varies by manufacturer (typically 200 J for most devices), so providers should know their equipment specifications 1

Resume CPR immediately after any shock delivery without pausing for rhythm or pulse checks—continue for 2 minutes before next rhythm assessment 1

Pediatric Considerations

For children with VF or pulseless VT:

• First shock: 2 J/kg 1
• Second shock: 4 J/kg 1
• Subsequent shocks: 4-10 J/kg, not to exceed adult maximum dose 1