What is the definition and management of cardiac arrest, a condition characterized by the cessation of blood circulation?

Cardiac Arrest: Definition and Management

Cardiac arrest is characterized by an abrupt loss of effective blood flow, sufficient to cause immediate loss of consciousness, leading immediately to death if untreated. 1

Definition of Cardiac Arrest

Cardiac arrest is defined as the sudden cessation of cardiac mechanical activity, confirmed by:

• Absence of a detectable pulse
• Unresponsiveness
• Apnea or agonal respirations 1

From a resuscitation perspective, sudden cardiac arrest (SCA) is defined as "malfunction or cessation of the electrical and mechanical activity of the heart, resulting in almost instantaneous loss of consciousness and collapse." 1

Pathophysiology

The pathophysiology of cardiac arrest is time-dependent and occurs in three phases:

1. Electrical phase (0-4 minutes):

   • Characterized by shockable rhythms (VF/pVT)
   • Heart is responsive to defibrillation
   • Highest chance of survival 1

2. Circulatory phase (4-10 minutes):

   • Characterized by tissue hypoxemia and emergence of asystole
   • CPR is crucial during this phase
   • Defibrillation is less effective 1

3. Metabolic phase (>10 minutes):

   • Characterized by asystole, worsening hypoxia, and metabolic factors
   • Survival is unlikely without advanced interventions
   • Often associated with severe functional disability 1

Presenting Rhythms in Cardiac Arrest

The most common electrical mechanisms for cardiac arrest include:

• Ventricular fibrillation (VF)
• Pulseless ventricular tachycardia (pVT)
• Asystole
• Pulseless electrical activity (PEA) 1

In adults, VF is the most common primary rhythm in sudden cardiac death, especially in victims of sudden, unheralded death. However, substantial numbers of cardiac arrests begin as severe bradyarrhythmias, asystole, or PEA. 1

Management of Cardiac Arrest

Immediate Actions

1. Activation of response team:

   • After establishing the presence of cardiac arrest, the first priority is activating a response team capable of identifying the specific mechanism and carrying out prompt intervention 1

2. High-quality CPR:

   • Chest compressions generate forward blood flow (30-40% of normal cardiac output)
   • Compression fraction should be >80% (minimize pauses)
   • Allow complete chest recoil
   • Avoid excessive compression rates 1

3. Early defibrillation (for shockable rhythms):

   • Deliver shocks of 200J, 200J, and 360J quickly (within 30-45 seconds)
   • Do not interrupt sequence with basic life support measures
   • Check rhythm or pulse after each shock 1

4. Airway management and ventilation:

   • Secure airway with endotracheal intubation if possible
   • Avoid excessive ventilation (target 10-12 breaths/minute)
   • Use highest available oxygen concentration initially 2

5. Vascular access and medication administration:

   • Establish IV/IO access
   • Administer epinephrine (1mg every 3-5 minutes)
   • Consider antiarrhythmic medications based on rhythm 1, 2

Identifying and Treating Reversible Causes

Systematically check for potentially reversible causes ("H's and T's") 2:

• Hypoxia: Ensure proper ventilation with 100% oxygen
• Hypovolemia: Rapid IV/IO fluid administration
• Hydrogen ion (acidosis): Ensure adequate ventilation
• Hypo/Hyperkalemia: Treat electrolyte imbalances
• Hypothermia: Active rewarming
• Toxins: Specific antidotes if available
• Cardiac tamponade: Pericardiocentesis
• Tension pneumothorax: Needle decompression
• Thrombosis (coronary): Consider emergent coronary angiography
• Thrombosis (pulmonary): Consider fibrinolytic therapy

Advanced Interventions

1. Point-of-care ultrasound:

   • Identify reversible causes with minimal interruption to chest compressions
   • Differentiate true PEA from pseudo-PEA 2

2. Mechanical CPR devices:

   • Consider when manual CPR is difficult to maintain
   • May provide more consistent compressions 3

3. Extracorporeal CPR (ECPR):

   • Consider for refractory cardiac arrest when reversible cause is suspected
   • Particularly valuable in prolonged arrests 4, 5

Post-Resuscitation Care

After return of spontaneous circulation (ROSC), focus on:

1. Targeted temperature management:

   • Target 32-36°C for comatose patients
   • Maintain for at least 24 hours
   • Prevent fever in all post-cardiac arrest patients 1, 2

2. Hemodynamic optimization:

   • Target MAP ≥65 mmHg
   • Treat post-cardiac arrest myocardial dysfunction 1

3. Ventilation management:

   • Avoid hyperoxia (target SpO₂ 94-98%)
   • Avoid hyperventilation (target PaCO₂ 40-45 mmHg) 1

4. Coronary angiography:

   • Emergency coronary angiography for patients with STEMI on ECG
   • Consider for cardiac arrest of presumed cardiac origin 2

5. Neurological prognostication:

   • Delay at least 72 hours after normothermia
   • Avoid premature withdrawal of care 1, 2

Pitfalls and Caveats

1. Assuming PEA is always non-cardiac: PEA can be caused by reversible conditions that require specific interventions beyond standard ACLS.

2. Excessive ventilation: Overzealous ventilation increases intrathoracic pressure, decreases venous return, and reduces cardiac output.

3. Prolonged interruptions in chest compressions: Even brief pauses significantly reduce coronary and cerebral perfusion pressures.

4. Delayed defibrillation: For shockable rhythms, early defibrillation is critical for survival.

5. Premature prognostication: Avoid withdrawal of care based on early clinical findings, as neurological recovery may continue for days to weeks.

6. Failure to identify and treat underlying cause: Cardiac arrest is often a symptom of an underlying condition that requires specific treatment.

7. Hyperoxia after ROSC: Excessive oxygen can cause oxidative stress and worsen neurological outcomes.