What is Severe Hypermagnesemia?
Severe hypermagnesemia is a life-threatening electrolyte disorder defined as serum magnesium concentration >2.2 mEq/L (normal: 1.3-2.2 mEq/L), most commonly occurring in the obstetric setting with IV magnesium therapy for preeclampsia/eclampsia, or in patients with renal dysfunction taking magnesium-containing medications. 1
Definition and Pathophysiology
- Hypermagnesemia represents an elevated serum magnesium concentration above the normal range of 1.3-2.2 mEq/L 1
- Magnesium is essential for ATPase function, sodium-potassium-calcium transport across cell membranes, and stabilization of excitable membranes 1
- At extremely elevated levels, hypermagnesemia disrupts normal cellular excitability and conduction, leading to cardiovascular and neuromuscular collapse 1, 2
Clinical Presentation
Neurological Manifestations
- Muscular weakness and paralysis 1
- Ataxia and drowsiness 1
- Confusion progressing to altered consciousness and coma 1, 2
Cardiovascular Manifestations
- Vasodilation and hypotension 1
- Bradycardia 1
- Ventricular arrhythmias 1
- Cardiorespiratory arrest and asystole 1, 3
Respiratory Manifestations
- Hypoventilation leading to respiratory failure 1
High-Risk Clinical Scenarios
Obstetric Setting (Most Common)
The most likely scenario for severe hypermagnesemia is in pregnant patients receiving IV magnesium sulfate for preeclampsia or eclampsia treatment. 1
Renal Dysfunction
- Patients with end-stage renal disease or acute renal failure taking magnesium-containing preparations (laxatives, antacids) are at extreme risk 4, 5, 6
- Even patients with normal renal function can develop fatal hypermagnesemia when magnesium-containing laxatives are retained in the gut, creating a continuous absorption reservoir 6
Iatrogenic Causes
- Magnesium hydroxide (milk of magnesia) for constipation is a common culprit 4, 3, 6
- Pre-operative bowel preparations containing magnesium in patients with unrecognized renal impairment 5
Critical Management According to AHA Guidelines
During Cardiac Arrest
For cardiac arrest with known or suspected hypermagnesemia, empirical IV calcium administration may be reasonable in addition to standard ACLS care (Class 2b recommendation). 1
- Calcium chloride 10%: 5-10 mL IV over 2-5 minutes 1
- OR calcium gluconate 10%: 15-30 mL IV over 2-5 minutes 1
Pre-Arrest Severe Cardiotoxicity
- Immediate discontinuation of all magnesium-containing therapies 2, 4
- IV calcium administration as above 1
- Aggressive IV fluid therapy 2
- Hemodialysis or continuous renal replacement therapy (CRRT) for severe cases, which is highly effective and lifesaving 4, 3
Critical Pitfalls and Caveats
Diagnostic Challenges
- Hypermagnesemia can mimic ST-elevation myocardial infarction with cardiogenic shock or septic shock, leading to misdiagnosis and delayed treatment 3
- ECG findings may include severe QRS widening and diffuse ST elevation 3
- The condition is often overlooked due to its relative unfamiliarity among clinicians 2, 4
Mortality Risk
- Even with prompt hemodialysis, severe hypermagnesemia frequently results in death, particularly when magnesium-containing laxatives remain in the gut as a continuous absorption source 6
- Fatal outcomes have been reported despite successful reduction of serum magnesium levels, due to irreversible cardiovascular and respiratory complications 4, 5, 6
Prevention Strategies
- Always verify intact renal function before administering magnesium-containing preparations 5
- Avoid large doses of magnesium salts in patients with any degree of renal impairment 5
- Regular monitoring of serum magnesium levels in high-risk populations (patients on magnesium therapy, those with renal dysfunction) 2, 4
Prognosis
- Severe hypermagnesemia carries significant mortality risk even with aggressive intervention 4, 5, 6
- Complications leading to death include junctional bradycardia, myocardial infarction, respiratory failure, and refractory shock 5, 6
- Timely recognition and immediate hemodialysis offer the best chance for survival 3