Absent deep tendon reflexes, respiratory depression, or bradycardia - stop magnesium and notify provider immediately.
Before you read
Test yourself first: 2 questions
Question 1 of 2
A client with hypermagnesemia from overuse of magnesium-containing antacids is admitted. Which assessment finding does the nurse expect?
Answer: B. Hypermagnesemia (above 2.1 mEq/L) depresses neuromuscular function, producing diminished or absent deep tendon reflexes, hypotension, bradycardia, lethargy, and respiratory depression. Hyperreflexia and tetany are signs of HYPOmagnesemia, not excess magnesium.
Question 2 of 2
A client with chronic alcohol use disorder has a magnesium of 1.0 mEq/L. Which finding should the nurse expect?
Answer: A. Hypomagnesemia increases neuromuscular excitability, producing positive Chvostek and Trousseau signs, tremors, hyperactive reflexes, and a risk of seizures. Hypomagnesemia commonly coexists with hypokalemia and hypocalcemia. Decreased reflexes occur with hypermagnesemia.
Keep the streak going with more questions like these, each with a full rationale.
What is hypermagnesemia?
Excess magnesium depresses the central nervous system and neuromuscular function, slowing everything down. Hallmark progression is loss of deep tendon reflexes, then respiratory depression, then cardiac arrest.
Key points to remember
- High magnesium depresses neuromuscular transmission, causing diminished or absent deep tendon reflexes, lethargy, and drowsiness.
- Loss of deep tendon reflexes is an early and important warning sign of rising magnesium.
- Cardiac effects include bradycardia, hypotension, prolonged PR and QRS, heart block, and cardiac arrest.
- Respiratory depression and shallow breathing occur as respiratory muscles are suppressed.
- Flushing, warmth, and a feeling of generalized weakness are common.
- Severe hypermagnesemia leads to coma, respiratory failure, and cardiac arrest.
Common causes
- Renal failure, Mg antacids/laxatives
- OB Mg sulfate overdose
Signs & symptoms
- ↓ DTRs → absent reflexes
- Flushing, warmth, ↓ BP
- Lethargy, drowsiness, weakness
Nursing priorities
- Assess deep tendon reflexes, respiratory rate/depth, and level of consciousness frequently to catch worsening early.
- Stop all magnesium sources, including magnesium-containing antacids, laxatives, and IV magnesium.
- Monitor cardiac rhythm and blood pressure for bradycardia and hypotension.
- Administer IV calcium gluconate as ordered to antagonize the neuromuscular and cardiac effects of magnesium.
- Prepare for dialysis in renal failure clients with severe hypermagnesemia.
Labs & values
Patient teaching
- Clients with kidney disease should avoid magnesium-containing antacids and laxatives (such as milk of magnesia) unless prescribed.
- Report muscle weakness, drowsiness, flushing, or difficulty breathing.
- Do not exceed recommended doses of over-the-counter magnesium products.
Red flags: report now
- Absent deep tendon reflexes, respiratory depression, or bradycardia - stop magnesium and notify provider immediately.
- Have IV calcium gluconate available as the antidote during magnesium infusions (for example preeclampsia).
- Respiratory arrest or cardiac arrest - call a code and begin resuscitation.
References
Clinical references for this topic
