Hypermagnesemia

Hypermagnesemia is an electrolyte disturbance in which there is an abnormally elevated level of magnesium in the blood. Usually this results in excess of magnesium in the body.

Hypermagnesemia occurs rarely because the kidney is very effective in excreting excess magnesium. It usually develops only in people with kidney failure who are given magnesium salts or who take drugs that contain magnesium (e.g. some antacids and laxatives). It is usually concurrent with hypocalcemia and/or hyperkalemia.

Metabolism
For a detailed description of magnesium homeostasis and metabolism see hypomagnesemia.

Symptoms

 * Weakness, nausea and vomiting
 * Impaired breathing
 * Decreased respirations
 * Hypotension
 * Hypercalcemia
 * Arrhythmia and Asystole
 * Decreased or absent deep tendon reflexes
 * Bradycardia

Arrhythmia and asystole are possible cardiac complications of hypermagnesemia. Magnesium acts as physiologic calcium blocker, which results in electrical conduction abnormalities.

Clinical consequences related to serum concentration:
 * 4.0 mEq/l           hyporeflexia
 * >5.0 mEq/l           Prolonged atrioventricular conduction
 * >10.0 mEq/l          Complete heart block
 * >13.0 mEq/l          Cardiac arrest

Note that the therapeutic range for the prevention of the pre-eclampsic uterine contractions is: 4.0-7.0 mEq/L. As per Lu and Nightingale, serum Mg2+ concentrations associated with maternal toxicity (also neonate depression - hypotonia and low Apgar scores) are:
 * 7.0-10.0 mEq/L - loss of patellar reflex
 * 10.0-13.0 mEq/L - respiratory depression
 * 15.0-25.0 mEq/L - altered atrioventricular conduction and (further) complete heart block
 * >25.0 mEq/L - cardiac arrest

Hypermagnesemia in renal failure
An evaluation of 515 patients on hemodialysis demonstrated that serum magnesium concentration lower than 2.77 mg/dL (1.14 mmol/L) is a significant predictor for increased all-cause mortality. While the mean serum magnesium concentration of this study population (2.77 mg/dL or 1.14 mmol/L) would be considered indicative of mild hypermagnesemia in the healthy population, serum magnesium concentrations in hemodialysis patients may be optimal at a higher concentration, in view of better survival under hemodialysis conditions, without causing severe and symptomatic hypermagnesemia. Consistently, lower magnesium levels were significantly associated with the presence of vascular calcification of the hand arteries in a study investigating 390 nondiabetic hemodialysis patients. These results suggest that higher serum magnesium concentrations may play an important protective role in the development of vascular calcification in hemodialysis patients. Results from a longitudinal study with end-stage renal disease patients suggest that hypermagnesemia may retard the development of arterial calcifications in end-stage renal disease. Significantly lower values of carotid intima-media thickness and aortic pulse wave velocity values, which are surrogate markers for vascular calcification, were observed in chronic kidney disease patients with high serum magnesium levels (0.90-1.32 mmol/L or 2.18-3.21 mg/dL) indicating a lower arteriosclerotic burden associated with a lower risk of cardiovascular events and mortality. Consequently, CKD patients with mildly elevated magnesium levels could have a survival advantage over those with lower magnesium levels.

Causes
Magnesium status depends on three organs: uptake in the intestine, storage in the bone and excretion in the kidneys. Hypermagnesemia is therefore often due to problems in these organs, mostly intestine or kidney.

Predisposing conditions

 * Haemolysis, magnesium concentration in erythrocytes is approximately three times greater than in serum, therefore hemolysis can increase plasma magnesium. Hypermagnesemia is expected only in massive hemolysis.
 * Renal insufficiency, excretion of magnesium becomes impaired when creatinine clearance falls below 30 ml/min. However, hypermagnesemia is not a prominent feature of renal insufficiency unless magnesium intake is increased.
 * Other conditions that can predispose to mild hypermagnesemia are diabetic ketoacidosis, adrenal insufficiency, hyperparathyroidism and lithium intoxication.

Therapy
Prevention of hypermagnesemia usually is possible. In mild cases, withdrawing magnesium supplementation is often sufficient. In more severe cases the following treatments are used:
 * Intravenous calcium gluconate, because the actions of magnesium in neuromuscular and cardiac function are antagonized by calcium.

Definitive treatment of hypermagnesemia requires increasing renal magnesium excretion through:
 * Intravenous diuretics, in the presence of normal renal function
 * Dialysis, when kidney function is impaired and the patient is symptomatic from hypermagnesemia