What are the reversible causes of cardiac arrest?

Reversible Causes of Cardiac Arrest

The reversible causes of cardiac arrest are categorized as the 4 Hs (Hypoxia, Hypovolemia, Hyper/hypokalemia and other electrolyte disorders, Hypothermia) and 4 Ts (Thrombosis - coronary or pulmonary, Tamponade - cardiac, Tension pneumothorax, Toxins). 1

The 4 Hs

Hypoxia

• Ensure adequate oxygenation through advanced airway management and ventilation to improve survival outcomes 1
• Avoid routine hyperventilation after restoration of circulation as it can lead to hypocapnia and additional cerebral ischemia 1
• Titrate inspired oxygen content appropriately in post-resuscitation care to minimize the risk of hypoxia 1

Hypovolemia

• Administer IV/IO crystalloid fluids (0.9% saline or lactated Ringer's solution) for severe volume loss 1
• Consider blood transfusion for cardiac arrest caused by severe blood loss to improve survival outcomes 1
• Rapid fluid resuscitation is critical as hypovolemia is a readily reversible cause of cardiac arrest 2

Hyper/hypokalemia and Other Electrolyte Disorders

• Identify and correct electrolyte abnormalities promptly to treat hyper/hypokalemia and metabolic disorders 1
• For hypokalemic cardiac arrest, rapid administration of intravenous potassium (10 mEq/100 mL of potassium chloride over 5 minutes) may be warranted despite concerns about rapid administration 3
• For hyperkalemic cardiac arrest, immediate treatment with calcium, insulin with glucose, and sodium bicarbonate is critical 1

Hypothermia

• For extremely cold victims with a perfusing rhythm, focus on preventing further heat loss 1
• Remove wet garments and insulate the victim from environmental exposures to prevent further heat loss 1
• Consider active rewarming techniques for severe hypothermia to improve survival outcomes 1

The 4 Ts

Thrombosis (Coronary or Pulmonary)

• For suspected pulmonary embolism, consider fibrinolytic therapy during cardiac arrest 1
• Avoid surgical embolectomy in patients who have received CPR due to high mortality 1
• Consider percutaneous mechanical thromboembolectomy for patients with cardiac arrest from pulmonary embolism 1
• For coronary thrombosis, early diagnosis and treatment of ST-elevation myocardial infarction is critical after ROSC 1

Tamponade (Cardiac)

• Perform pericardiocentesis guided by echocardiography for cardiac arrest associated with cardiac tamponade 1
• If echocardiography is unavailable, non-image-guided pericardiocentesis is an acceptable alternative 1
• Point-of-care ultrasound can help identify cardiac tamponade with high specificity (100%) but should not interrupt chest compressions 4

Tension Pneumothorax

• Perform needle decompression if tension pneumothorax is clinically suspected as the cause of PEA 1
• Tension pneumothorax requires immediate intervention to relieve pressure and restore cardiac output 2

Toxins

• For drug overdose and poisoning, identify the specific toxin and administer appropriate antidotes 1
• For cyanide poisoning, administer cyanide-antidote therapy with a cyanide scavenger 1
• For carbon monoxide poisoning, consider hyperbaric oxygen therapy 1
• For opioid toxicity, naloxone administration is indicated, but be aware that abrupt reversal may result in adverse effects including pulmonary edema and cardiac arrest in some patients 5

Diagnostic Approaches

• Point-of-care ultrasound (POCUS) may be considered as an additional diagnostic tool when clinical suspicion for a specific reversible cause is present, but should not interrupt CPR 4
• Any deployment of diagnostic POCUS during CPR should be carefully considered and weighed against the risks of interrupting chest compressions and misinterpreting the sonographic findings 4
• POCUS has shown high sensitivity and specificity for cardiac tamponade (100%), pulmonary embolism (100% sensitivity, 97% specificity), and myocardial infarction (86% sensitivity, 94% specificity) when performed by experienced personnel 4

Special Considerations

• In young adults (<40 years), cardiac arrest may be due to inherited or acquired cardiac disease or noncardiac causes including drug overdose, pulmonary embolism, subarachnoid hemorrhage, seizure, anaphylaxis, and infection 6
• Implement comprehensive treatment protocols including therapeutic hypothermia, glucose control, goal-directed hemodynamic optimization, appropriate ventilation, and percutaneous coronary intervention when indicated 1
• Extracorporeal CPR (eCPR) or mechanical CPR should be considered for bridging the period needed to reverse the precipitating cause(s) in select cases 2

Common Pitfalls to Avoid

• Delaying transcutaneous pacing in unstable bradycardia patients who don't respond to atropine can lead to poor outcomes 1
• Administering atropine in patients with high-degree AV block may worsen the condition and should be avoided 1
• Routine hyperventilation after ROSC can cause cerebral ischemia and should be avoided 1
• Failing to identify and treat the underlying reversible cause promptly, as time-critical interventions may even prevent cardiac arrest if applied early 2
• Interrupting chest compressions for prolonged diagnostic procedures, as continuous high-quality CPR remains essential while searching for reversible causes 4