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Hypermagnesemia

Anesthesia Implications

Updated On: July 10, 2026

Anesthesia Implications

Emergency treatment - IV calcium and/or hemodialysis. Altered hemodynamics - Arterial and/or central lines are recommended where the patient is severely hypotensive and/or in need of aggressive fluid resuscitation. Avoid acidosis - acidosis will exacerbate hypermagnesemia NMB sensitive - Hypermagnesemia will prolong neuromuscular blockade. Some recommend reducing the dose 25-50%. Use TOF to guide NMB doses.

Pathophysiology

Definition - Hypermagnesemia is defined as a serum magnesium of greater than 2.5 mEq/L Etiology - primarily caused by magnesium supplementation (eg. IV administered magnesium, antacids, magnesium-based enemas, or cathartics). Poor renal function is a common comorbidity when the cause is supplementation. Other less common causes can include hypothyroidism, rhabdomyolysis, lithium supplementation, hyperparathyroidism, and addison's disease (adrenal insufficiency). Diagnosis - creatinine clearance (renal function) is typically assessed along with identification of magnesium supplements. Once ruled out, other causes would be investigated (eg. hypothyroidism, lithium supplementation, hyperparathyroidism, and addison's disease). Symptoms and magnesium blood levels (mEq/L):

  • 4-5 : lethargy, nausea, vomiting, facial flushing
  • 7-10 : Loss of deep tendon reflexes
  • 10-13 : Respiratory paralysis
  • >= 15 : Cardiac conduction abnormalities
  • > 25 : Cardiac arrest
    • Rare - Much less common than hypomagnesemia. Found primarily in ICU and dialysis patients. Treatment - acute cases are treated with IV calcium and/or hemodialysis. Less severe cases aim to increase renal excretion by using loop diuretics and saline bolus'. Half percent normal saline with 5% dextrose is the recommended solution. Ionized - 60% of magnesium in the blood is ionized. This ionized magnesium is responsible for clinical manifestations.

    Reference

    Hines. Stoelting’s anesthesia and co-existing disease. 7th edition. 2018.
    Herroeder. Magnesium—Essentials for Anesthesiologists. 2011