What is the immediate treatment for a patient with a shockable rhythm, such as ventricular fibrillation or pulseless ventricular tachycardia?

Immediate Treatment for Shockable Rhythm (VF/pVT)

For patients with ventricular fibrillation or pulseless ventricular tachycardia, immediately perform high-quality CPR and defibrillate as soon as the defibrillator is available—defibrillation with concurrent high-quality CPR is the only intervention proven to improve survival in shockable rhythms. 1

Initial Management Algorithm

Step 1: Immediate Defibrillation

• Deliver the first shock immediately upon rhythm confirmation without delay 1, 2
• Use biphasic defibrillators with initial energy of 200J (or manufacturer-recommended dose) 1, 3
• If witnessed arrest with defibrillator immediately available on-site, start CPR and use defibrillator as soon as possible 1
• Minimize pre-shock pause to less than 10 seconds—shorter pauses are associated with higher survival rates 3

Step 2: Resume CPR Immediately After Shock

• Immediately resume chest compressions after shock delivery without checking pulse or rhythm 1, 2
• Continue high-quality CPR for 2 minutes (5 cycles at 30:2 ratio) 1
• Adequate compression depth (at least 2 inches in adults) and rate (100-120/min) while minimizing pauses 1
• Charge defibrillator during chest compressions to minimize peri-shock pause 3

Step 3: Rhythm Check and Second Shock

• After 2 minutes of CPR, briefly pause to check rhythm 1
• If VF/pVT persists, deliver second shock immediately 1, 2
• Resume CPR immediately after shock 1

Step 4: Medication Administration After Third Shock

• If VF/pVT persists after 2-3 defibrillation attempts, administer epinephrine 1 mg IV/IO 1, 2
• Continue epinephrine 1 mg IV/IO every 3-5 minutes throughout resuscitation 1, 2
• Consider antiarrhythmic medication for shock-refractory VF/pVT: 1, 2
  • Amiodarone 300 mg IV/IO (first dose), OR 1, 2, 4
  • Lidocaine 1-1.5 mg/kg IV/IO if amiodarone unavailable 1, 2
• If VF/pVT recurs after successful defibrillation, give second dose of amiodarone 150 mg IV/IO 4

Critical Timing Considerations

CPR Before Defibrillation: When to Consider

• For unwitnessed arrest or when defibrillator arrival is delayed >5 minutes, perform CPR while obtaining defibrillator 1, 5
• Evidence shows CPR before defibrillation may improve outcomes when EMS response time exceeds 5 minutes 1, 5
• However, if defibrillator is immediately available, do not delay shock for CPR 1, 2

Medication Timing Rationale

• Prioritize defibrillation over medication administration—establishing vascular access should never compromise CPR quality or timely defibrillation 1, 2
• Epinephrine after initial shocks (rather than immediately) is recommended because early defibrillation is more likely to restore perfusing rhythm in fresh VF/pVT 1, 2
• For non-shockable rhythms (asystole/PEA), give epinephrine immediately as soon as IV/IO access obtained 1, 2

High-Quality CPR Requirements

Compression Technique

• Minimize interruptions in chest compressions—chest compressions performed only 51-76% of time in observational studies, but higher compression fraction improves outcomes 1
• Interruptions for rhythm analysis should be <10 seconds 1
• Frequent or prolonged interruptions associated with decreased defibrillation success and reduced survival 1

After Advanced Airway Placement

• Once endotracheal tube or supraglottic airway placed, provide continuous chest compressions at 100-120/min without pauses 1
• Deliver ventilations at 1 breath every 6 seconds (10 breaths/min) 1
• Rotate compressor every 2 minutes to prevent fatigue 1

Refractory VF/pVT Management

If VF/pVT Persists After Standard Measures

• Continue CPR with minimal interruptions 1
• Ensure adequate compression depth and rate 1
• Consider reversible causes (H's and T's) 1
• Vector-change defibrillation: Change pad position from anterolateral to anterior-posterior if initial attempts unsuccessful 3
• Double sequential defibrillation may be attempted after ≥3 failed shocks, though evidence is limited and conflicting 3, 6

Important Clinical Caveats

What NOT to Do

• Never delay defibrillation to establish IV access or administer medications 1, 2
• Never check pulse immediately after shock—resume compressions immediately 1, 2
• Never use high-dose epinephrine (>1 mg)—no survival benefit demonstrated 1, 2
• Never substitute vasopressin for epinephrine—no advantage over standard epinephrine 1, 2

Realistic Expectations About Medications

• Neither epinephrine nor antiarrhythmics improve long-term survival or favorable neurological outcomes 1, 2
• Epinephrine increases ROSC and short-term survival through vasoconstriction but may increase survival with poor neurological outcome 1, 2
• Amiodarone and lidocaine improve ROSC and hospital admission rates but not survival to discharge 1, 2
• The primary determinants of survival remain high-quality CPR and early defibrillation 1

Monitoring During Resuscitation

• If available, use end-tidal CO2 monitoring—maintain ETCO2 ≥10 mmHg during CPR as marker of adequate compressions 1
• Abrupt rise in ETCO2 (>40 mmHg) or visible arterial pulsations suggest ROSC 1
• Use physiological feedback (compression depth monitors, ETCO2) to optimize CPR quality 1