What is the role of magnesium sulfate in cardiac arrest?

Role of Magnesium Sulfate in Cardiac Arrest

Magnesium sulfate should NOT be administered routinely during cardiac arrest management but is specifically indicated for cardiac arrest associated with torsades de pointes (polymorphic ventricular tachycardia with prolonged QT interval). 1

Indications for Magnesium Sulfate in Cardiac Arrest

Recommended Use:

• Torsades de pointes: When VF/pulseless VT cardiac arrest is associated with torsades de pointes, IV/IO magnesium sulfate is indicated (Class IIb, LOE C) 1
  • Dosage: 1-2 g IV/IO bolus diluted in 10 mL D5W 1
  • Mechanism: Magnesium stabilizes excitable membranes and facilitates termination of torsades de pointes 1

Not Recommended:

• Routine use in cardiac arrest: Three randomized controlled trials failed to show benefit from routine magnesium administration during cardiac arrest (Class III, LOE A) 1, 2
• Regular/monomorphic VT with normal QT interval: Magnesium is not effective in terminating these arrhythmias 1

Special Situations Where Magnesium May Be Considered

1. Hypomagnesemia-related cardiotoxicity:

   • For cardiotoxicity and cardiac arrest associated with documented hypomagnesemia, IV magnesium 1-2 g bolus is recommended (Class I, LOE C) 1
   • Patients with low ionized magnesium levels (<0.40 mmol/L) and cardiac arrhythmias show better response to magnesium supplementation (88% effectiveness) compared to those with normal levels (17% effectiveness) 3

2. Medication-induced QT prolongation with recurrent torsades de pointes:

   • Intravenous magnesium is recommended to suppress arrhythmia (Class I, LOE C-LD) 1
   • Particularly important with medications known to cause QT prolongation, such as certain proton pump inhibitors 4

3. Electrolyte management during cardiac arrest:

   • Magnesium repletion to normal values (≥2.0 mmol/L) is beneficial for patients with torsades de pointes associated with acquired QT prolongation (Class I, LOE C-LD) 1

Administration Protocol

When indicated for torsades de pointes during cardiac arrest:

1. Administer 1-2 g IV/IO bolus of magnesium sulfate
2. Dilute in 10 mL D5W
3. Give as rapid IV/IO push
4. May consider additional doses if torsades de pointes persists, though optimal dosing regimen is not established 1

Potential Adverse Effects

• Vasodilation and hypotension if administered too rapidly 1
• At extremely high serum levels: depressed consciousness, bradycardia, hypoventilation 1
• In cases of hypermagnesemia-induced cardiac arrest, calcium administration (calcium chloride 10% 5-10 mL or calcium gluconate 10% 15-30 mL IV) may be considered as an antidote (Class IIb, LOE C) 1

Clinical Pearls and Pitfalls

• Common pitfall: Using magnesium indiscriminately in all cardiac arrest cases rather than specifically for torsades de pointes
• Important consideration: Hypomagnesemia is far more common than hypermagnesemia and is associated with poor prognosis in cardiac arrest patients 1
• Practical note: The 2018 AHA guidelines reaffirm that magnesium should not be used routinely during cardiac arrest but maintain its recommendation for torsades de pointes 1
• Clinical caveat: Even in refractory ventricular fibrillation in the prehospital setting, magnesium administration (2g) failed to improve short or long-term survival compared to placebo 2

By following these evidence-based guidelines, clinicians can appropriately utilize magnesium sulfate in cardiac arrest situations where it is most likely to benefit patients while avoiding unnecessary administration in cases where it provides no survival benefit.