Why is magnesium sulfate stopped in a pregnant patient during cardiac arrest?

Stopping Magnesium Sulfate During Cardiac Arrest in Pregnant Patients

Magnesium sulfate should be immediately discontinued in pregnant patients who experience cardiac arrest because it can worsen cardiovascular depression and interfere with resuscitation efforts. 1

Mechanism and Risks of Magnesium Sulfate During Cardiac Arrest

• Magnesium sulfate causes cardiac effects including prolonged PR, QRS, and QT intervals at levels of 2.5-5 mmol/L, and can progress to AV nodal conduction block, bradycardia, hypotension, and cardiac arrest at levels of 6-10 mmol/L 1
• During cardiac arrest, magnesium sulfate can further depress myocardial contractility and vascular tone, potentially reducing the effectiveness of resuscitation efforts 1
• Magnesium toxicity can cause respiratory depression, severe muscular weakness, and loss of tendon reflexes at levels of 4-5 mmol/L, which may complicate resuscitation 1

Evidence-Based Recommendations for Management

• The American Heart Association (AHA) explicitly states in their cardiac arrest management algorithm for pregnant patients: "If patient receiving IV magnesium prearrest, stop magnesium" 1
• Routine administration of magnesium sulfate in cardiac arrest is not recommended (Class III: No Benefit) unless specifically treating torsades de pointes 2
• If magnesium sulfate was being administered prior to arrest, it should be immediately discontinued as part of the initial management 1, 2

Antidote Administration

• Empirical calcium administration is recommended as a direct antidote for magnesium toxicity 1
• The AHA guidelines specifically recommend giving IV calcium chloride 10 mL in 10% solution, or calcium gluconate 30 mL in 10% solution if the patient was receiving magnesium sulfate prior to arrest 1
• Injectable calcium should be immediately available to counteract potential magnesium intoxication in pregnant patients receiving magnesium sulfate 3

Special Considerations in Pregnant Patients

• Iatrogenic magnesium overdose is a recognized risk in pregnant women receiving magnesium sulfate, particularly if the woman becomes oliguric 1
• Hypermagnesemia from magnesium sulfate administration is specifically listed as an important iatrogenic cause of maternal cardiac arrest 1
• Concomitant use of other medications that interact with magnesium sulfate (such as calcium channel blockers, diuretics) may increase the risk of cardiopulmonary complications 4

Prevention of Magnesium-Related Cardiac Arrest

• Clinical indicators of safe magnesium dosage include the presence of patellar reflex (knee jerk) and absence of respiratory depression (≥16 breaths/minute) 3
• Knee jerk reflexes should be tested before each dose of magnesium sulfate, and if absent, no additional magnesium should be given until reflexes return 3
• Serum magnesium levels should be monitored, with therapeutic levels for seizure control ranging from 2.5 to 5 mEq/L 3

Resuming Magnesium After Successful Resuscitation

• The decision to resume magnesium sulfate after successful resuscitation should be carefully evaluated based on the original indication and the patient's clinical status 1
• If magnesium sulfate was being used for seizure prophylaxis in preeclampsia, alternative anticonvulsant therapy may need to be considered 1

By immediately stopping magnesium sulfate during cardiac arrest in pregnant patients and administering calcium as an antidote when needed, healthcare providers can optimize the chances of successful maternal resuscitation and improve outcomes for both mother and fetus.