Hypermagnesemia

Pts with renal insufficiency, especially those receiving Mg ²⁺ -containing cathartics or antacids.

Parturients on MgSO ₄ therapy.

“Runaway” infusion of Mg ²⁺ during transportation to the OR can cause acute, life-threatening hypermagnesemia. Risk of developing very high serum Mg ²⁺ levels in such cases can be reduced by always using a small-volume buretrol device in pts receiving IV Mg ²⁺ therapy.

Treatment of preeclampsia, eclampsia, and preterm labor.

Evidence indicates that Mg ²⁺ therapy reduces the risk of cerebral palsy in women at risk of preterm delivery.

Treatment of ventricular dysrhythmias, especially torsades de pointes.

Treatment of severe asthma in pts who have not responded to initial therapy.

Treatment of migraine.

Lowers risk of metabolic syndrome.

Potentiates nondepolarizing neuromuscular blocking agents.

May increase risk of modest hypotension during administration of regional anesthesia.

Potentiates hypotension associated with use of volatile anesthetics, CCBs, and butyrophenones.

Can exacerbate local anesthetic toxicity.

Hypermagnesemia may be associated with increased in bleeding time and TEG changes, although no clinically significant coagulopathies have been attributed to Mg ²⁺ .

Intraop hypotension

Muscle weakness (especially respiratory)

Excessive sedation

Myocardial depression and cardiorespiratory arrest with very high levels

Defined as an elevated Mg ²⁺ concentration in plasma, in excess of 1.1 mmol/L.

Equivalent Mg ²⁺ concentrations in the three unit systems in common use: mg/dL, mEq/L, mmol/L.

• Normal serum level 1.8–2.4 mg/dL, 1.5–2.0 mEq/L, 0.75–1.0 mmol/L.

• Therapeutic level 4.8–8.4 mg/dL, 4–7 mEq/L, 2–3.5 mmol/L.

• Neuromuscular toxic level greater than 12 mg/dL, greater than 10 mEq/L, greater than 5 mmol/L.

Mg ²⁺ elimination is dependent on GFR; with GFR less than 30 mL/min, pts are at significant risk.

Signs and symptoms vary with plasma concentration and become more serious as the plasma concentration increases greater than 4 mmol/L.

CV, respiratory, and MS systems are predominantly affected.

• Pts with chronic renal failure frequently have Mg ²⁺ levels up to 3 mmol/L but are seldom symptomatic.

• Acidemia will decrease serum level at which side effects occur; e.g., in presence of acidemia, cardiac arrest can occur at a serum level of 8–10 mmol/L.