8.2 VF/pVT & Defibrillation Energy

Shockable Rhythms: VF and Pulseless VT

When the monitor shows ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT) in a child without a pulse, the definitive therapy is electrical defibrillation. High-quality CPR buys time and may convert fine VF to a more shockable waveform, but only a shock (or spontaneous conversion) terminates the chaotic/reentrant electrical activity that prevents coordinated output.

Recognition

Critical trap: Wide-complex tachycardia with a pulse is not treated with unsynchronized defibrillation as the first step in a conscious/unstable-with-pulse pathway—that is synchronized cardioversion or other tachycardia care. Pulseless VT is cardiac arrest: unsynchronized defibrillation.

Defibrillate as soon as possible

For VF/pVT:

1. Continue CPR while pads are applied and the defibrillator charges when feasible (peri-shock CPR).
2. Clear the patient and deliver one shock.
3. Immediately resume CPR for about 2 minutes (starting with compressions).
4. Brief rhythm check; if still VF/pVT, shock again at the next energy step and resume CPR.
5. Obtain IV/IO access; give epinephrine per timing rules (below and Section 8.4).
6. Consider antiarrhythmics for refractory VF/pVT per PALS (e.g., amiodarone 5 mg/kg IV/IO bolus context in later pharmacology chapters).

Do not deliver stacked shocks as a routine modern approach. Single shock → immediate CPR maximizes coronary perfusion pressure recovery after the brief pause.

Pediatric Defibrillation Energy Doses (Memorize Cold)

Weight-based energy is a high-frequency PALS written and megacode item. Align with exam-meta and 2025-era PALS teaching:

Worked examples

• 10 kg infant: first shock 20 J (2 J/kg); next 40 J (4 J/kg).
• 20 kg child: first 40 J; next 80 J.
• 40 kg child: first 80 J; next 160 J. If escalating further, stay ≤ 10 J/kg (400 J) and ≤ device adult max.

If your manual defibrillator only allows certain steps (e.g., 50 J, 100 J), choose the closest appropriate energy without routinely underdosing when a higher appropriate step is available—follow device design and local protocol while respecting the 2 J/kg → 4 J/kg → ≤10 J/kg/adult max framework.

Pads, paddles, and attenuators

• Use pediatric pads or paddles sized/positioned for the child when available.
• Ensure pads do not touch; use anterolateral or anteroposterior placement as appropriate for size.
• For AEDs, use a pediatric dose attenuator / pediatric pads when available for infants and young children per device instructions. If a pediatric system is not available and the child is in arrest with a shockable rhythm, use the standard AED rather than withholding defibrillation.
• Remove medication patches in the pad field; dry the chest; avoid placing pads over implanted devices.

Minimize the peri-shock pause

Coronary perfusion pressure falls within seconds when compressions stop. Team choreography:

• Charge during CPR when the device allows
• Clear loudly and visually
• Shock
• Hands back on the chest in 1–2 seconds
• No routine immediate post-shock pulse check—resume CPR first; assess rhythm/pulse at the next coordinated 2-minute check unless clear signs of ROSC appear (e.g., abrupt ETCO₂ rise, purposeful movement)

Integrating Epinephrine on the Shockable Path

On the shockable pathway, defibrillation is the priority when a defibrillator is immediately available. Do not postpone the first shock to draw up epinephrine. PALS teaching places epinephrine after defibrillation attempts as the algorithm directs: commonly after shocks have begun (often framed as after the second attempt in many course algorithms) and sooner if defibrillation is not immediately possible (for example, delayed device arrival while CPR is ongoing).

Practical exam rules of thumb:

• Device ready + VF/pVT → shock first
• Continue CPR, get access, give epinephrine 0.01 mg/kg IV/IO every 3–5 minutes once the shock sequence is underway per algorithm timing
• Never let drug preparation create long hands-off intervals

Refractory VF/pVT

If VF/pVT persists after CPR, defibrillation, and epinephrine:

• Recheck pad contact and energy dose
• Continue high-quality CPR and shock cycles
• Give antiarrhythmic therapy as indicated (amiodarone 5 mg/kg IV/IO is the classic PALS arrest bolus; lidocaine is an alternative in many algorithms)
• Relentlessly seek reversible causes (toxins, channelopathy triggers, electrolyte crises, coronary anomalies, etc.)

Clinical scenario

A 15 kg child collapses; pads show coarse VF. First shock = 2 J/kg = 30 J (or closest device setting). Immediate CPR. At 2 minutes, still VF → shock 4 J/kg = 60 J, resume CPR, ensure IO/IV, give epinephrine 0.01 mg/kg, continue cycles. Escalate energy if refractory while staying ≤ 10 J/kg (150 J) and ≤ adult max.

Bottom line for 8.2: VF/pVT → defibrillate ASAP → 2 J/kg first (reasonable 2–4 J/kg) → subsequent 4 J/kg (may increase, ≤10 J/kg or adult max) → single shock + immediate CPR → pediatric pads/attenuator when available → epinephrine after defibrillation priority when rapid defib is possible.