Stop the infusion and notify the provider for absent deep tendon reflexes, respirations under 12, or urine output under 30 mL/hr.
Before you read
Test yourself first: 5 questions
Question 1 of 5
A client at 28 weeks gestation in preterm labor is started on magnesium sulfate. The nurse understands that in addition to its tocolytic effect at this gestational age, magnesium sulfate is given for which purpose?
Answer: A. When given to women in preterm labor before about 32 weeks gestation, magnesium sulfate provides fetal neuroprotection, reducing the risk of cerebral palsy and severe motor dysfunction in the preterm infant. This is in addition to its use to relax the uterus.
Question 2 of 5
A client in preterm labor at 30 weeks is started on magnesium sulfate. The nurse monitors for toxicity. Which finding is the earliest sign of magnesium sulfate toxicity requiring the nurse to stop the infusion?
Answer: B. Loss of deep tendon reflexes is an early warning sign of magnesium sulfate toxicity. Other signs include respiratory depression below 12 per minute and decreased urine output. The antidote is calcium gluconate.
Question 3 of 5
A client receiving IV magnesium sulfate develops respiratory depression and absent reflexes. Which medication should the nurse anticipate administering?
Answer: B. Calcium gluconate is the antidote for magnesium toxicity; it antagonizes the neuromuscular and cardiac depressant effects of excess magnesium. The nurse should stop the magnesium infusion and prepare calcium gluconate. Potassium chloride, sodium bicarbonate, and naloxone do not reverse magnesium toxicity.
Question 4 of 5
A client in preterm labor at 30 weeks is receiving intravenous magnesium sulfate. Which assessment finding indicates magnesium toxicity and requires immediate action?
Answer: A. Loss of deep tendon reflexes is an early sign of magnesium sulfate toxicity and precedes respiratory depression and cardiac arrest. The nurse should stop the infusion, notify the provider, and have calcium gluconate available as the antidote. Brisk reflexes and normal respirations are reassuring.
Question 5 of 5
A client with hypomagnesemia is prescribed IV magnesium sulfate. Which assessment finding indicates magnesium toxicity?
Answer: B. Magnesium toxicity depresses neuromuscular and cardiac function; the loss of deep tendon reflexes is an early and key warning sign. Other signs include respiratory depression, hypotension, and decreased level of consciousness. Brisk reflexes, hypertension, and tachypnea are not signs of magnesium toxicity.
Keep the streak going with more questions like these, each with a full rationale.
What is magnesium sulfate therapy?
It works by relaxing smooth muscle and depressing neuromuscular transmission. Because it has a narrow therapeutic range, the nurse must continuously monitor for toxicity. Antidote memory aid: Calcium gluconate reverses magnesium toxicity.
Key points to remember
- It depresses the central nervous system and relaxes smooth muscle, reducing seizure activity and uterine contractions.
- The therapeutic serum range for seizure prophylaxis is about 4-7 mEq/L; normal serum magnesium is 1.3-2.1 mEq/L.
- Early toxicity appears as loss of deep tendon reflexes, the first warning sign.
- Progressive toxicity causes respiratory depression, decreased urine output, hypotension, and eventually cardiac arrest.
- Because it is renally excreted, low urine output rapidly raises serum levels and toxicity risk.
- Outside obstetrics, IV magnesium treats severe hypomagnesemia and the dysrhythmia torsades de pointes.
Nursing priorities
- Assess deep tendon reflexes, respiratory rate, blood pressure, and level of consciousness hourly during infusion.
- Monitor urine output and keep it at 30 mL/hr or more, since the drug is excreted by the kidneys.
- Use an infusion pump and frequently verify the rate to prevent accidental overdose.
- Keep calcium gluconate readily available at the bedside as the antidote for magnesium toxicity.
- Monitor the fetal heart rate and newborn for respiratory depression and decreased muscle tone after birth.
Labs & values
Patient teaching
- Expect to feel warm, flushed, or sleepy during the infusion; report difficulty breathing or feeling unable to move.
- Tell the nurse if you feel weak, very drowsy, or have trouble urinating.
- Frequent assessments are normal and necessary to keep you safe on this medication.
Red flags: report now
- Stop the infusion and notify the provider for absent deep tendon reflexes, respirations under 12, or urine output under 30 mL/hr.
- Administer calcium gluconate immediately for signs of serious magnesium toxicity.
- Report a serum magnesium level above the therapeutic range or signs of cardiac changes.
- Watch the newborn for hypotonia and respiratory depression if the mother received magnesium near delivery.
References
Clinical references for this topic
