ACLS & Cardiac Arrest — Part 1: BLS Foundation, High-Quality CPR & Defibrillation

1. The Chain of Survival

The chain of survival is the conceptual framework upon which all resuscitation systems are built. Each link in the chain represents a critical intervention; weakness in any single link substantially reduces the probability of neurologically intact survival. The concept has evolved from its original four-link model into separate chains for out-of-hospital cardiac arrest (OHCA) and in-hospital cardiac arrest (IHCA), reflecting the distinct pathways and resources available in each setting.^{1 2}

1.1 Out-of-Hospital Cardiac Arrest (OHCA) Chain of Survival

1.2 In-Hospital Cardiac Arrest (IHCA) Chain of Survival

2. High-Quality Cardiopulmonary Resuscitation

High-quality CPR is the single most important determinant of survival from cardiac arrest, more so than any advanced intervention. The quality of chest compressions directly determines coronary perfusion pressure and cerebral blood flow during arrest. Multiple observational studies and meta-analyses have demonstrated that deviations from optimal CPR parameters are associated with decreased survival.^{1 3 4}

2.1 Chest Compression Parameters

2.2 Ventilation During CPR

Ventilation parameters vary based on the phase of resuscitation and whether an advanced airway is in place:

The danger of hyperventilation: Excessive ventilation rates increase intrathoracic pressure, reduce venous return and cardiac output during CPR, decrease coronary and cerebral perfusion pressures, cause gastric insufflation (increasing aspiration risk), and are independently associated with worse outcomes. Providers consistently tend to ventilate too fast; deliberate coaching and use of timing devices help maintain the target rate of 10 breaths per minute.^{1 3}

2.3 Mechanical CPR Devices

Mechanical CPR devices (load-distributing band devices and piston-based devices) provide consistent, high-quality chest compressions without rescuer fatigue. Key evidence and recommendations:^{1 6}

• Mechanical CPR has not demonstrated superiority over high-quality manual CPR in large randomized controlled trials (LINC, CIRC, PARAMEDIC)
• Mechanical CPR is a reasonable alternative when sustained high-quality manual compressions are impractical:
  • During transport (ambulance movement makes manual CPR unreliable)
  • During prolonged resuscitations
  • In the cardiac catheterization laboratory
  • During preparation for extracorporeal CPR (ECPR)
  • In settings with limited personnel
• Application of the device should not interrupt chest compressions for more than 10 seconds

3. Automated External Defibrillation (AED)

Early defibrillation is the most critical intervention for ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT). For every minute that defibrillation is delayed, survival from witnessed VF decreases by approximately 7–10% without bystander CPR, and by 3–4% per minute with bystander CPR.^{1 2 7}

3.1 AED Application and Use

3.2 Special AED Considerations

• Hairy chest: Rapidly shave pad sites or use a second set of pads to pull off hair, then apply fresh pads
• Wet patient: Rapidly dry the chest before pad application
• Implanted pacemaker/defibrillator: Place pads at least 1 inch (2.5 cm) away from the device; standard anterior-lateral placement typically suffices
• Transdermal medication patches: Remove patch and wipe the area clean before pad placement
• Children (1–8 years): Use pediatric dose-attenuator pads/key if available; if not available, use standard adult AED
• Infants (<1 year): Manual defibrillator preferred; if unavailable, AED with pediatric pads; if pediatric pads unavailable, adult AED is acceptable

4. Manual Defibrillation

4.1 Defibrillation Energy Levels

Energy requirements vary by device waveform. Modern biphasic defibrillators are more effective at lower energy levels than older monophasic devices.^{1 2 8}

Key principles:

• If the provider is unsure of the device’s recommended first-shock energy, use the maximum available energy ¹
• A single shock strategy is recommended (one shock followed by immediate CPR) rather than stacked shocks
• Immediately resume CPR after shock delivery — do not pause to recheck rhythm; the next rhythm check occurs after 2 minutes of CPR
• Time from last compression to shock delivery (pre-shock pause) should be minimized to <10 seconds

4.2 Defibrillation Pad/Paddle Placement

Pad placement in special populations:

• Women: Place left lateral pad under the left breast; avoid placing pad on breast tissue
• Obese patients: Standard anterior-lateral or anterior-posterior; may need firmer pressure if using paddles
• Pregnancy: Standard anterior-lateral; no modification required for defibrillation energy
• Implanted devices: Pads at least 1 inch from device generator

4.3 Defibrillation Troubleshooting

5. Refractory Ventricular Fibrillation

Refractory VF is defined as VF that persists after three or more appropriately delivered shocks with concurrent high-quality CPR and standard ACLS pharmacotherapy. This occurs in approximately 10–25% of patients presenting with VF/pVT cardiac arrest and is associated with significantly worse outcomes.^{6 8 9}

5.1 Strategies for Refractory VF

5.2 Double Sequential Defibrillation Protocol

1. Ensure two defibrillators are available with separate sets of pads
2. Place the first set of pads in the standard anterior-lateral position
3. Place the second set of pads in the anterior-posterior position (avoiding overlap with first set)
4. Charge both defibrillators to maximum energy
5. Deliver both shocks simultaneously or in rapid sequence (within 1 second of each other)
6. Immediately resume CPR for 2 minutes before next rhythm assessment

6. Waveform Capnography During CPR

End-tidal carbon dioxide (ETCO2) monitoring via continuous waveform capnography is the most useful real-time physiologic monitor during cardiac arrest resuscitation. It provides objective feedback on CPR quality, can confirm advanced airway placement, and has prognostic value.^{1 2 11}

6.1 Physiologic Basis

During cardiac arrest, CO2 transport from tissues to the lungs is entirely dependent on cardiac output generated by chest compressions. ETCO2 therefore serves as a surrogate marker for the cardiac output produced during CPR:

• Higher ETCO2 = better cardiac output from compressions = better coronary and cerebral perfusion
• A sudden sustained rise in ETCO2 (typically to 35–40 mmHg or higher) during CPR strongly suggests return of spontaneous circulation (ROSC)
• ETCO2 values are also affected by ventilation rate, sodium bicarbonate administration, and epinephrine

6.2 ETCO2 Targets and Interpretation During CPR

6.3 Limitations of ETCO2 During Arrest

• Sodium bicarbonate administration causes transient ETCO2 spike (CO2 liberated from bicarbonate-acid reaction) — not indicative of ROSC or improved CPR quality
• Epinephrine may cause a transient decrease in ETCO2 by redistributing pulmonary blood flow
• Excessive ventilation rate will lower ETCO2 without reflecting a change in cardiac output
• ETCO2 values are less reliable with supraglottic airways compared to endotracheal tubes due to potential air leak

7. CPR Feedback Devices and Quality Improvement

Real-time CPR feedback devices (accelerometer-based, force-sensing, or audiovisual) provide immediate guidance to the compressor on rate, depth, recoil, and hand position. Evidence supports their use for improving adherence to CPR quality targets:^{1 4}

• Audiovisual feedback devices improve compression rate and depth during both training and real resuscitations
• Metronome-guided CPR improves compression rate consistency
• Debriefing after resuscitation events (using CPR performance data) improves team performance in subsequent events
• Systems-based quality improvement programs that track compression fraction, pre-shock pause duration, and ETCO2 are associated with improved survival at the institutional level

7.1 Recommended CPR Quality Metrics for System Monitoring

8. Physiologic Monitoring-Guided Resuscitation

Emerging evidence supports the use of real-time physiologic monitoring — beyond ETCO2 — to guide resuscitation efforts and individualize care during cardiac arrest.^{1 6 11}

8.1 Arterial Line-Guided CPR

In patients with an arterial line in place at the time of arrest (primarily IHCA):

• Diastolic blood pressure (DBP): Target diastolic arterial pressure >25 mmHg during CPR; this correlates with coronary perfusion pressure
• Coronary perfusion pressure (CPP): CPP = aortic diastolic pressure minus right atrial diastolic pressure; values >15 mmHg are associated with ROSC; values >20 mmHg are optimal
• Arterial line monitoring allows real-time titration of compression quality and vasopressor dosing
• A sudden increase in arterial pulsatility suggests ROSC

8.2 Ultrasound During Cardiac Arrest (Point-of-Care Echocardiography)

Point-of-care echocardiography during cardiac arrest can identify reversible causes and guide management, but must be performed without interrupting chest compressions:^{2 6}

Technique: Use the subxiphoid or parasternal long-axis view during the rhythm analysis pause (do not prolong the pause beyond 10 seconds). Pre-position the probe during CPR so that image acquisition occurs immediately when compressions pause.

References