THERAPEUTIC USE OF MAGNESIUM IN ANESTHESI A AND INTENSIVE-CARE

Magnesium (Mg), a cofactor in numerous enzymatic reactions, is often i gnored by clinicians, as the symptomatology of Mg depletion is not spe cific and usually associated with that of the cause of the depletion. Futhermore, the plasma Mg concentration (0.8 to 1.1 mmol . L(-1)) is o nly equivalent to one percent of the total body content, A Mg deficit may exist while plasma Mg concentration is normal. Therefore other tec hniques for Mg assessment, such as the repletion test, as well as red blood cell and lymphocyte concentrations have been used. A renewed int erest for Mg occurred as numerous studies have shown the therapeutic e fficiency of Mg and as the mechanisms of its haemodynamic effects have been recognized. Mg regulates Na-K-ATPase activity, K channels activi ty and, most of all, it is a natural calcium channel blocking agent, T hese properties explain its important plate in electrophysiology of my ocardial cells and the effects on the tension of smooth muscles, resul ting in a vasodilation and a bronchodilation respectively. The antagon istic effect of Mg on calcium decreases the presynaptic release of ace tylcholine at the neuromuscular junction and the release of epinephrin e at the peripheral sympathic nerves and the adrenals. Mg potentiates the effect of non-depolarizing muscle relaxants. A Mg deficiency occur s often in ICU patients, in alcoholics and during use of diuretics, Si multaneous administration of Mg is often required for treatment of pot assium deficiency. Mg has an anti-arrhythmic effect towards digoxin-me diated dysrhythmias and torsades de pointes, and can be efficient in o ther arrhythmias. Systematic use of Mg seems to decrease mortality of acute myocardial infarction and is justified during cardiac surgery, o ften associated with hypomagnesemia, because of vasodilation of corona ry arteries and in order to prevent occurrence of arrhythmias. Mg, bec ause of its calcium channel blocking properties and as it lowers the r elease of epinephrine, is indicated for surgery of pheochromocytoma. I n eclamptic and pre-eclamptic patients, the use of Mg is valuable, but not as an anti-epileptic agent. Other clinical uses of Mg have been p roposed, but they are either anecdotal or of uncertain efficiency.