What are the reversible causes of cardiac arrest and their treatments?

Reversible Causes of Cardiac Arrest and Their Treatments

The reversible causes of cardiac arrest are commonly categorized as the "4 Hs and 4 Ts" (Hypoxia, Hypovolemia, Hyper/hypokalemia and metabolic disorders, Hypothermia, Thrombosis-coronary or pulmonary, Tamponade-cardiac, Tension pneumothorax, and Toxins), each requiring specific targeted treatments to improve survival outcomes. 1

The 4 Hs

Hypoxia

• Ensure adequate oxygenation through advanced airway management and ventilation 2
• Avoid routine hyperventilation after restoration of circulation as it can lead to hypocapnia and additional cerebral ischemia 2
• Titrate inspired oxygen content appropriately in post-resuscitation care 2

Hypovolemia

• Administer IV/IO crystalloid fluids (0.9% saline or lactated Ringer's solution) for severe volume loss 2
• Consider blood transfusion for cardiac arrest caused by severe blood loss 2
• Use rapid infusion with cold fluids which appears to be well-tolerated 2

Hyper/hypokalemia and Metabolic Disorders

• Identify and correct electrolyte abnormalities promptly 2
• For patients with high potassium levels (>7 mmol/L), immediate treatment is critical as this can be incompatible with survival, particularly in avalanche victims 2
• Use point-of-care ultrasound to help identify metabolic causes when performed by experienced operators 3

Hypothermia

• For extremely cold victims with a perfusing rhythm, focus on preventing further heat loss 2
• Remove wet garments and insulate the victim from environmental exposures 2
• Consider active rewarming techniques for severe hypothermia 2
• Note that avalanche victims are unlikely to survive if buried >35 minutes with obstructed airway and core temperature <32°C 2

The 4 Ts

Thrombosis (Coronary or Pulmonary)

• For suspected pulmonary embolism, consider fibrinolytic therapy during cardiac arrest 2
• Avoid surgical embolectomy in patients who have received CPR due to high mortality 2
• Consider percutaneous mechanical thromboembolectomy for patients with cardiac arrest from pulmonary embolism who are not candidates for fibrinolytic therapy 2
• For coronary thrombosis, early diagnosis and treatment of ST-elevation myocardial infarction is critical after ROSC 2

Tamponade (Cardiac)

• Perform pericardiocentesis guided by echocardiography for cardiac arrest associated with cardiac tamponade 2
• If echocardiography is unavailable, non-image-guided pericardiocentesis is an acceptable alternative 2
• Use point-of-care ultrasound to diagnose cardiac tamponade, limiting scanning time to minimize interruptions in chest compressions 3, 4

Tension Pneumothorax

• Perform needle decompression if tension pneumothorax is clinically suspected as the cause of PEA 2
• Consider ultrasound for diagnosis if available and operator is experienced 4
• Ensure minimal interruption to chest compressions during diagnostic procedures 3

Toxins

• For drug overdose and poisoning, identify the specific toxin and administer appropriate antidotes 2
• For cyanide poisoning (common in fire victims), administer cyanide-antidote therapy with a cyanide scavenger (IV hydroxocobalamin or IV sodium nitrite/inhaled amyl nitrite), followed by IV sodium thiosulfate 2
• For carbon monoxide poisoning, consider hyperbaric oxygen therapy, especially in patients with severe toxicity 2

Special Considerations

Use of Point-of-Care Ultrasound

• While no studies specifically examine the impact on patient outcomes, ultrasound can provide valuable information about 2:
  • Intravascular volume status
  • Presence of cardiac tamponade
  • Mass lesions (tumor, clot)
  • Left ventricular contractility
  • Regional wall motion abnormalities
• POCUS should be incorporated into cardiac arrest algorithms to identify thrombotic and obstructive causes 4

Post-Cardiac Arrest Care

• Implement comprehensive treatment protocols including 2:
  • Therapeutic hypothermia for comatose patients
  • Glucose control
  • Goal-directed hemodynamic optimization
  • Appropriate ventilation
  • Percutaneous coronary intervention when indicated
• Avoid routine hyperventilation leading to hypocapnia 2
• Consider IV fluids as part of post-arrest care package 2

Specific Populations

• Young adults (<40 years) with cardiac arrest require evaluation for 5:
  • Basic metabolic profile and serum troponin
  • Urine toxicology test
  • Electrocardiogram
  • Chest x-ray
  • Head-to-pelvis computed tomography
  • Bedside ultrasound for pericardial tamponade, aortic dissection, or hemorrhage
• Traumatic cardiac arrest requires modified approach focusing on immediate treatment of underlying causes 3

Common Pitfalls to Avoid

• Delaying transcutaneous pacing in unstable bradycardia patients who don't respond to atropine 6
• Administering atropine in patients with high-degree AV block, which may worsen the condition 6
• Routine hyperventilation after ROSC, which can cause cerebral ischemia 2
• Prolonged interruptions in chest compressions during diagnostic procedures 3
• Failing to consider and treat reversible causes early in the resuscitation process 1