RESUMO
A wide variation in the prevalence of total serum hypomagnesemia in intensive care unit patients has been reported. This work aims to assess body magnesium deficiency in critically ill patients using different approaches and to evaluate its relationship to other electrolyte disturbances and clinical outcome. The study included 43 adult critically ill patients and 20 healthy controls. Laboratory parameters carried out on admission and every 24 hours for 3 days included: serum electrolytes, serum and erythrocyte total magnesium [RBCMg]. Twenty four hour urinary magnesium was determined before and after IV magnesium loading. Mg retention was defined as excretion of < 70% of the magnesium load. At admission, RBCMg was significantly lower in patients than controls [p = 0.008] whereas serum magnesium was not significantly different. Twenty one patients were magnesium retainers, only 9 of whom were hypomagnesemic. All non-retainers were normomagnesemic. Magnesium retainers had significantly lower RBCMg, serum potassium and calcium than non-retainers [p = 0.0007, 0.004 and 0.007 respectively]. In retainers, retention% negatively correlated to RBCMg and serum potassium. In both retainers and non-retainers, RBCMg positively correlated to serum potassium whereas serum magnesium did not correlate to any of the other parameters of magnesium status. Magnesium retainers had significantly longer ICU stay and a higher mortality rate. Magnesium deficiency is common in critically ill patients and is associated with hypocalcemia, hypokalemia and a poor clinical outcome