[Indications for the use of magnesium in anesthesia and intensive care]. / Indications du magnésium en anesthésie-réanimation.

Magnesium (Mg), a cofactor in numerous enzymatic reactions, is often ignored by clinicians, as the symptomatology of Mg depletion is not specific and usually associated with that of the cause of the depletion. Furthermore, the plasma Mg concentration (0.8 to 1.1 mmol.L-1) is only equivalent to one percent of the total body content. A Mg deficit may exist while plasma Mg concentration is normal. Therefore other techniques for Mg assessment, such as the repletion test, as well as red blood cell and lymphocyte concentrations have been used. A renewed interest for Mg occurred as numerous studies have shown the therapeutic efficiency of Mg and as the mechanisms of its haemodynamic effects have been recognized. Mg regulates Na-K-ATPase activity, K channels activity and, most of all, it is a natural calcium channel blocking agent. These properties explain its important place in electrophysiology of myocardial cells and the effects on the tension of smooth muscles, resulting in a vasodilation and a bronchodilation respectively. The antagonistic effect of Mg on calcium decreases the presynaptic release of acetylcholine at the neuromuscular junction and the release of epinephrine at the peripheral sympathetic nerves and the adrenals. Mg potentiates the effect of non-depolarizing muscle relaxants. A Mg deficiency occurs often in ICU patients, in alcoholics and during use of diuretics. Simultaneous administration of Mg is often required for treatment of potassium deficiency. Mg has an anti-arrhythmic effect towards digoxin-mediated dysrhythmias and torsades de pointes, and can be efficient in other arrhythmias. Systematic use of Mg seems to decrease mortality of acute myocardial infarction and is justified during cardiac surgery, often associated with hypomagnesemia, because of vasodilation of coronary arteries and in order to prevent occurrence of arrhythmias. Mg, because of its calcium channel blocking properties and as it lowers the release of epinephrine, is indicated for surgery of pheochromocytoma. In 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 proposed, but they are either anecdotal or of uncertain efficiency.

[Importance of plasma (histamine and tryptase) and urinary (methylhistamine) in peri-anesthetic anaphylactic and/or anaphylactoid reactions]. / Intérêt des médiateurs plasmatiques (histamine et tryptase) et urinaire (méthylhistamine) lors des réactions anaphylactiques et/ou anaphylactoïdes peranesthésiques.

Histamine and tryptase, released during anaphylactoid reactions in anaesthesia, can be measured out by radioimmunoassay, provided that their own pharmacokinetic is respected. For two years, we have used sample kits in order to realize the measuring out of these mediators. The aim of this study was to evaluate the interest of these mediators within investigational procedures for anaphylactoid reactions. Eleven anaphylactoid reactions were observed (0,03%). The early blood samples (the first ten minutes following onset of the reaction) were made only in 36% of the cases. Within the serious reactions (grade III), the raising of tryptase indicates the involvement of mast-cell activation. Within minor clinical reactions (grade I), plasma histamine and urinary methylhistamine were the only mediators detected. In an anaphylactic reaction of grade II, which happened after the administering of vecuronium, tryptase was not detected. Therefore, these mediators give the anaesthetists the possibility to prove quickly the severity of the reactions and to direct the investigations very early towards the right way.

[Is hemodilution sufficient to avoid homologous blood transfusion in reduction mammaplasties?]. / L'hémodilution est-elle suffisante pour éviter la transfusion homologue au cours des mammoplasties de réduction?

The unpredictability of blood loss during reductive mammoplasties induced the authors to use a blood-sparing technique so as to avoid homologous transfusions. Intentional isovolaemic haemodilution (IIH) was performed in 38 patients. Clinical and biological criteria were used for analyzing the results. In this prospective study, IIH could not prevent the necessity of homologous transfusion for 3 patients, in the early postoperative period. In one of these cases, clotting of blood prevented its utilization. Therefore IIH appears to be an interesting alternative blood-sparing method in patients who cannot benefit easily from preoperative programmed blood auto-donation.