A pregnant client with severe preeclampsia is started on IV magnesium sulfate and has a serum magnesium level of 15 mEq/L. Which manifestation is expected?

• A. Respiratory distress
• B. ECG changes
• C. Loss of reflexes
• D. Cardiac arrest

Answer: (A)

High levels of magnesium sulfate suppress neuromuscular transmission, especially affecting the respiratory muscles. When the serum level is as high as 15 mEq/L, this depression becomes profound, leading to weakened or ineffective breathing. The most expected finding is respiratory distress or failure due to diaphragmatic and intercostal muscle weakness. This is why continuous evaluation of respiratory rate, depth, and oxygenation is critical, and why stopping the infusion and administering calcium gluconate are key emergency steps if respiratory compromise develops. While other toxicity signs like slowed reflexes or ECG changes can occur, the urgent, life-threatening issue at this level is respiratory depression.