ACLS Algorithm for Cardiac Arrest
For adult cardiac arrest, immediately initiate high-quality CPR with chest compressions at a rate of 100-120/min and depth of at least 2 inches (5 cm), minimize interruptions, and use early defibrillation for shockable rhythms—this sequence forms the foundation of the ACLS algorithm and represents the only interventions proven to improve survival. 1
Initial Recognition and Activation (Box 1-2)
- Check for responsiveness by tapping the victim's shoulder and shouting "Are you all right?" 1
- Simultaneously assess breathing and pulse within 10 seconds—look for no breathing or only gasping while checking for a definite pulse 1
- Immediately activate the emergency response system if the patient is unresponsive with no breathing or only gasping 1
- Retrieve the AED/defibrillator and emergency equipment (or send someone to do so) 1
Critical pitfall: Healthcare providers often take too long checking for a pulse and have difficulty determining if one is present—if you don't definitively feel a pulse within 10 seconds, start compressions immediately 1
High-Quality CPR (Box 4)
- Compression rate: 100-120/min 1
- Compression depth: At least 2 inches (5 cm) 1
- Allow complete chest recoil after each compression 1
- Minimize interruptions in chest compressions to less than 10 seconds 1
- Avoid excessive ventilation which decreases cardiac output 1, 2
- Perform cycles of 30 compressions to 2 breaths until an advanced airway is placed 1
- Change compressor every 2 minutes or sooner if fatigued 1
Rhythm Check and Defibrillation
Shockable Rhythms (VF/Pulseless VT)
- Deliver 1 shock immediately when VF/pVT is identified 1
- Resume CPR immediately for 2 minutes after the shock without pausing to check rhythm 1
- Establish IV/IO access during CPR 1
- Administer epinephrine 1 mg IV/IO every 3-5 minutes 1, 2
- For shock-refractory VF/pVT (after 2-3 shocks), administer either amiodarone OR lidocaine 1:
Key evidence update: The 2018 AHA guidelines removed the preference for amiodarone over lidocaine, as neither has demonstrated improved long-term survival or neurological outcomes 1. A 2023 study of in-hospital cardiac arrest actually found lidocaine associated with slightly better outcomes (3.3% absolute improvement in survival to discharge) compared to amiodarone 3. Either agent is acceptable; choose based on availability and familiarity.
Non-Shockable Rhythms (Asystole/PEA)
- Continue high-quality CPR 1
- Establish IV/IO access 1
- Administer epinephrine 1 mg IV/IO every 3-5 minutes—this is particularly important for non-shockable rhythms where epinephrine improves survival 1, 2
- Search for and treat reversible causes (H's and T's) 2
Advanced Airway Management
- Place endotracheal tube or supraglottic airway when feasible without prolonged interruption of compressions 1
- Confirm placement with waveform capnography—ETCO₂ <10 mmHg suggests inadequate CPR quality 1, 2
- Once advanced airway is placed: Provide continuous chest compressions with 1 breath every 6 seconds (10 breaths/min) 1, 2
- Monitor capnography continuously—an abrupt sustained increase in ETCO₂ to >40 mmHg indicates return of spontaneous circulation 1, 2
Reversible Causes (H's and T's)
Systematically evaluate and treat 2:
- Hypovolemia: IV fluid bolus 2
- Hypoxia: Ensure 100% oxygen and adequate ventilation 2
- Hydrogen ion (acidosis): Adequate ventilation 2
- Hypo/hyperkalemia: Check and correct electrolytes 2
- Hypothermia: Rewarm if accidental 2
- Tension pneumothorax: Needle decompression 2
- Tamponade (cardiac): Pericardiocentesis 2
- Toxins: Specific antidotes (e.g., naloxone for opioid overdose) 2
- Thrombosis (pulmonary): Consider thrombolytics 2
- Thrombosis (coronary): Urgent coronary angiography if indicated 2
Recognition of ROSC
Stop CPR and check for ROSC when you observe 1, 2:
- Definite pulse and blood pressure return
- Abrupt sustained increase in ETCO₂ (typically >40 mmHg)
- Spontaneous arterial pressure waves on intra-arterial monitoring
Post-ROSC Care
- Maintain adequate oxygenation: Target SpO₂ 94-98% to avoid both hypoxemia and hyperoxemia 2
- Maintain normocapnia by adjusting ventilation 2
- Support hemodynamics: Maintain MAP ≥65 mmHg with vasopressors as needed 2
- Obtain 12-lead ECG immediately to identify ST-elevation MI 2
- Consider urgent coronary angiography for suspected cardiac etiology 2
- Initiate targeted temperature management for all patients who don't follow commands after ROSC 1, 2
- Monitor and treat seizures which are common post-arrest 2
CPR Quality Monitoring
Use these metrics to optimize CPR 1:
- ETCO₂: If <10 mmHg, improve CPR quality (compression depth/rate)
- Intra-arterial diastolic pressure: If <20 mmHg, improve CPR quality
- Continuous feedback devices when available
Critical point: CPR and defibrillation are the ONLY interventions proven to improve survival in VF/pVT cardiac arrest—all medications (epinephrine, amiodarone, lidocaine) improve short-term outcomes like ROSC but have not demonstrated improved long-term survival or neurological outcomes 1. Therefore, never delay high-quality compressions or defibrillation to administer medications.