In a patient receiving IV magnesium sulfate for preeclampsia, which sign would indicate toxicity?

In a patient receiving IV magnesium sulfate for preeclampsia, which sign would indicate toxicity?

• A. Tachycardia
• B. Decreased deep tendon reflexes
• C. Elevated blood pressure
• D. Hyperglycemia

Answer: (D)

Magnesium sulfate toxicity shows up as excessive central nervous system and neuromuscular suppression. The most reliable early clue is a decrease or loss of deep tendon reflexes. This occurs because magnesium blocks calcium influx at the neuromuscular junction and depresses nerve transmission, so as levels rise, reflexes fade and respiratory function can later be affected. Hyperglycemia is not produced by magnesium toxicity, and tachycardia or elevated blood pressure aren’t typical signs of magnesium overload (toxicity more often accompanies bradycardia and hypotension). The key clinical signal to act on is diminished deep tendon reflexes, which prompts stopping the infusion and initiating appropriate management, including calcium gluconate if indicated and close monitoring of respiratory status and vital signs.

Magnesium sulfate toxicity shows up as excessive central nervous system and neuromuscular suppression. The most reliable early clue is a decrease or loss of deep tendon reflexes. This occurs because magnesium blocks calcium influx at the neuromuscular junction and depresses nerve transmission, so as levels rise, reflexes fade and respiratory function can later be affected.

Hyperglycemia is not produced by magnesium toxicity, and tachycardia or elevated blood pressure aren’t typical signs of magnesium overload (toxicity more often accompanies bradycardia and hypotension). The key clinical signal to act on is diminished deep tendon reflexes, which prompts stopping the infusion and initiating appropriate management, including calcium gluconate if indicated and close monitoring of respiratory status and vital signs.