What is the algorithm for cardiopulmonary resuscitation (CPR) in a patient who has experienced cardiac arrest?

CPR Algorithm for Cardiac Arrest

Immediately begin high-quality chest compressions at 100-120/min with a depth of at least 2 inches (5 cm) as soon as cardiac arrest is recognized—this is the single most critical intervention for survival. 1

Initial Recognition and Response

• Check for responsiveness by tapping the victim's shoulder and shouting while simultaneously assessing breathing—look specifically for absent breathing or only gasping respirations (agonal gasps are common and should NOT be mistaken for normal breathing). 2

• Activate the emergency response system immediately if the victim is unresponsive with no breathing or only gasping. 2

• Check for a pulse but spend no more than 10 seconds doing this—if you don't feel a pulse or are uncertain, immediately start CPR because pulse checks are notoriously unreliable even among trained providers. 2, 1

• Retrieve an AED (if nearby and easily accessible) or send a second rescuer to get it while you begin compressions. 2

High-Quality CPR Technique

Chest Compressions

• Compression rate: 100-120 per minute (not faster, not slower). 2, 1
• Compression depth: At least 2 inches (5 cm) but avoid exceeding 2.4 inches (6 cm). 2, 1
• Hand position: Lower half of the sternum. 2
• Allow complete chest recoil between each compression—do not lean on the chest as this impairs venous return. 2, 1
• Minimize interruptions: Keep total preshock and postshock pauses as short as possible, ideally under 10 seconds for delivering breaths. 2
• Change compressor every 2 minutes or sooner if fatigued to maintain quality. 2, 1

Compression-to-Ventilation Ratio

For rescuers WITHOUT an advanced airway:

• Deliver 30 compressions followed by 2 breaths, pausing compressions for less than 10 seconds to deliver the breaths. 2, 1
• Each breath should be delivered over approximately 1 second, just enough to make the chest rise. 2

For rescuers WITH an advanced airway (endotracheal tube or supraglottic airway):

• Deliver continuous chest compressions without pauses at 100-120/min. 2, 1
• Deliver 1 breath every 6 seconds (10 breaths per minute) asynchronously without interrupting compressions. 2, 1
• Use manual ventilation (bag-valve-mask, self-inflating bag) rather than mechanical ventilators during CPR, as modern ventilators erroneously sense chest compressions as spontaneous breaths and deliver excessive ventilation rates. 3

Critical Pitfall: Avoid Excessive Ventilation

Excessive ventilation decreases venous return, reduces cardiac output, and worsens outcomes—deliver only enough volume to make the chest rise. 2, 3

Defibrillation Protocol

• Turn on the AED and follow prompts immediately when it arrives. 2

For shockable rhythms (VF/pulseless VT):

• Deliver one shock using biphasic defibrillator at 120-200 Joules (or manufacturer recommendation) or monophasic at 360 Joules. 2, 1
• Resume CPR immediately after the shock without checking pulse or rhythm—continue for 2 minutes. 2, 1
• Check rhythm every 2 minutes and repeat shock if VF/pulseless VT persists. 2

For non-shockable rhythms (PEA/asystole):

• Resume CPR immediately for 2 minutes, then recheck rhythm. 2

Advanced Life Support Components

Medications

• Epinephrine 1 mg IV/IO every 3-5 minutes throughout the resuscitation. 2, 1
• For refractory VF/pulseless VT: Consider amiodarone 300 mg IV/IO bolus (second dose 150 mg) or lidocaine 1-1.5 mg/kg IV/IO (second dose 0.5-0.75 mg/kg). 2

Airway Management

• Consider advanced airway (endotracheal intubation or supraglottic airway) once advanced providers arrive. 2, 1
• Use waveform capnography to confirm and monitor tube placement—PETCO2 monitoring is essential. 2, 1
• Once advanced airway is placed, switch to continuous compressions with 1 breath every 6 seconds. 2, 1

Recognition of Return of Spontaneous Circulation (ROSC)

Stop CPR and check for ROSC if you observe:

• Palpable pulse and measurable blood pressure. 2, 1
• Abrupt sustained increase in PETCO2 ≥40 mmHg (most reliable indicator). 2, 1
• Spontaneous arterial pressure waves on invasive monitoring. 2, 1

When ROSC is achieved, immediately transition to post-cardiac arrest care. 1

Reversible Causes (H's and T's)

Search for and treat reversible causes:

• H's: Hypovolemia, Hypoxia, Hydrogen ion (acidosis), Hypo-/hyperkalemia, Hypothermia. 2
• T's: Tension pneumothorax, Tamponade (cardiac), Toxins, Thrombosis (pulmonary), Thrombosis (coronary). 2

Special Considerations for Lay Rescuers

Untrained bystanders should provide compression-only CPR (no breaths) when instructed by emergency dispatchers—this improves survival compared to no CPR. 2, 4

Trained lay rescuers should provide 30 compressions to 2 breaths if able to perform rescue breathing. 2

Evidence Note on Compression-Only vs. Conventional CPR

High-quality evidence shows that bystander-administered compression-only CPR increases survival to hospital discharge by 2.4% compared to interrupted compressions with rescue breathing (14% vs 11.6%). 4 However, when performed by EMS professionals, continuous compressions with asynchronous breathing did not improve outcomes and may slightly reduce survival compared to 30:2 ratio. 5 This supports the current guideline recommendations differentiating lay rescuer from professional rescuer approaches.