Which sign would most clearly indicate magnesium sulfate toxicity in a laboring patient?

Which sign would most clearly indicate magnesium sulfate toxicity in a laboring patient?

• A. Absent deep tendon reflexes.
• B. Blood pressure 150/90.
• C. Respiratory rate 12/minute.
• D. Urine output 200 ml/4 hours.

Answer: (A)

Magnesium sulfate toxicity shows up first as neuromuscular and respiratory depression, with the most reliable early clue being loss of deep tendon reflexes. Magnesium dampens neuromuscular transmission, so when levels rise into the toxic range, reflexes fade as a clear, objective sign before other problems become obvious. That makes the absence of deep tendon reflexes the best indicator that the drug level is dangerously high. Other signs can occur, but they’re less specific. A high blood pressure can happen for various reasons and isn’t a diagnostic marker of magnesium toxicity. A respiratory rate of 12 per minute might be normal or could reflect early fatigue, but on its own it isn’t as definitive as absent reflexes. Urine output of 200 mL in four hours shows kidneys are clearing fluid adequately at that moment and doesn’t directly signal magnesium toxicity. If absent reflexes are observed, the prudent action is to stop the magnesium infusion and notify the clinician, as this suggests toxicity. Calcium gluconate can be used as the antidote if toxicity is suspected.

Magnesium sulfate toxicity shows up first as neuromuscular and respiratory depression, with the most reliable early clue being loss of deep tendon reflexes. Magnesium dampens neuromuscular transmission, so when levels rise into the toxic range, reflexes fade as a clear, objective sign before other problems become obvious. That makes the absence of deep tendon reflexes the best indicator that the drug level is dangerously high.

Other signs can occur, but they’re less specific. A high blood pressure can happen for various reasons and isn’t a diagnostic marker of magnesium toxicity. A respiratory rate of 12 per minute might be normal or could reflect early fatigue, but on its own it isn’t as definitive as absent reflexes. Urine output of 200 mL in four hours shows kidneys are clearing fluid adequately at that moment and doesn’t directly signal magnesium toxicity.

If absent reflexes are observed, the prudent action is to stop the magnesium infusion and notify the clinician, as this suggests toxicity. Calcium gluconate can be used as the antidote if toxicity is suspected.