Which finding indicates magnesium sulfate toxicity when used to manage preeclampsia?

Which finding indicates magnesium sulfate toxicity when used to manage preeclampsia?

• A. Proteinuria of 3+
• B. Respirations of 10 breaths per minute
• C. Presence of deep tendon reflexes
• D. Urine output of 20 mL in an hour

Answer: (B)

Magnesium sulfate lowers seizure risk by depressing the central nervous system, but if levels get high it can also suppress the respiratory drive. A respiratory rate of 10 breaths per minute shows respiratory depression from magnesium toxicity, making it the clearest warning sign among the options. Presence of deep tendon reflexes tends to indicate that toxicity hasn’t occurred yet; in actual toxicity, those reflexes are often diminished or absent. Proteinuria and low urine output reflect the underlying preeclampsia or renal status rather than magnesium toxicity itself. If toxicity is suspected, stop the infusion and follow protocol (e.g., monitor closely and have calcium gluconate available as an antidote).

Magnesium sulfate lowers seizure risk by depressing the central nervous system, but if levels get high it can also suppress the respiratory drive. A respiratory rate of 10 breaths per minute shows respiratory depression from magnesium toxicity, making it the clearest warning sign among the options. Presence of deep tendon reflexes tends to indicate that toxicity hasn’t occurred yet; in actual toxicity, those reflexes are often diminished or absent. Proteinuria and low urine output reflect the underlying preeclampsia or renal status rather than magnesium toxicity itself. If toxicity is suspected, stop the infusion and follow protocol (e.g., monitor closely and have calcium gluconate available as an antidote).