Effect of Magnesium Sulfate Infusion Rate on Magnesium Retention in Critically Ill Patients

Hypomagnesemia (low magnesium) is an electrolyte imbalance commonly found in up to 65% of critically ill patients. Possible consequences of hypomagnesemia include neuromuscular and neurologic dysfunction, heart arrhythmias, and alterations in other electrolytes. Data has shown that critically ill patients with hypomagnesemia have a significantly higher mortality rate than patients with a normal magnesium level. The most simple and commonly used test to diagnose hypomagnesemia is a serum magnesium level. Based on the magnesium level and symptoms of hypomagnesemia, patients may be replaced with either oral or intravenous (IV) magnesium. When replacing magnesium via the IV route, approximately half of the dose is retained by the body while the remainder is excreted in the urine. The low retention rate is due to the slow uptake of magnesium by cells and decreased magnesium reabsorption by the kidneys in response to the delivery of a large concentration of magnesium. The purpose of this study is to determine whether an eight hour compared to a four hour infusion of IV magnesium sulfate results in a greater retention of the magnesium dose.