A primigravida receiving magnesium sulfate for gestational hypertension is assessed every 30 minutes. Which finding is most concerning?

A primigravida receiving magnesium sulfate for gestational hypertension is assessed every 30 minutes. Which finding is most concerning?

• A. Urinary output of 20 mL
• B. Deep tendon reflexes 2+
• C. Fetal heart rate 120 beats per minute
• D. Respiratory rate 10 breaths per minute

Answer: (D)

Magnesium sulfate for seizure prevention can depress the central nervous system and the muscles involved in breathing. The most urgent warning sign of toxicity is respiratory depression, because a slowed or shallow respirations directly threaten oxygenation and can lead to respiratory arrest. In this scenario, a reduced breathing rate signals that magnesium levels are high enough to compromise ventilation, requiring immediate action to stop the infusion, support or secure the airway, and notify the provider (calcium gluconate may be used as antidote if ordered). Other findings like low urine output or reflex changes can indicate toxicity risk, and a fetal heart rate within the normal range adds reassurance for the fetus, but they don’t convey the immediate danger the depressed respiratory rate does.

Magnesium sulfate for seizure prevention can depress the central nervous system and the muscles involved in breathing. The most urgent warning sign of toxicity is respiratory depression, because a slowed or shallow respirations directly threaten oxygenation and can lead to respiratory arrest. In this scenario, a reduced breathing rate signals that magnesium levels are high enough to compromise ventilation, requiring immediate action to stop the infusion, support or secure the airway, and notify the provider (calcium gluconate may be used as antidote if ordered). Other findings like low urine output or reflex changes can indicate toxicity risk, and a fetal heart rate within the normal range adds reassurance for the fetus, but they don’t convey the immediate danger the depressed respiratory rate does.