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Magnesium deficiency in the surgical intensive care unit

Introduction

Magnesium (Mg) deficiency is a common and yet underdiagnosed problem. Mg deficiency has been demonstrated in 50% of all ICU patients. These patients have significantly higher morbidity and mortality rate. The aim of this work was to detect the presence of Mg deficiency using a Mg loading test and to evaluate the safety and efficacy of Mg replacement therapy in cancer patients after major gut surgery.

Methods

Sixty adult patients admitted to the ICU after major GIT surgery were enrolled in the study, on the basis of a documented Mg serum level < 0.8 mmol/l on arrival at the ICU. Exclusion criteria were cardiac disease, liver dysfunction or serum creatinine > 1.3. Patients were randomly allocated to one of two groups: the Mg group received 20 mmol (5 g) Mg sulfate, infused daily over 6 hours for 3 days; and a control group received an equivalent amount of 5% dextrose. In the Mg group the next scheduled dose of MgSO4 was held if a serum magnesium level > 1.1 mmol/l, hypotension or bradycardia was recorded. Baseline and daily measurements of serum Mg, potassium, sodium, calcium and creatinine were done. Twenty-four-hour urine collection was used to determine the total urinary excretion of Mg. The net Mg balance (total Mg given – total urine Mg) was calculated. In the Mg group, Mg-deficient patients (retainers) who excreted < 70% of the Mg given ((urine Mg in mmol/daily Mg given) × 100) and Mg nondeficient patients (nonretainers) who excreted > 70% of the total Mg given were recorded.

Results

Patients in the Mg group showed a statistically significant increase in mean serum Mg at days 1, 2, and 3 compared with the control group and with day 0 (0.73 ± 0.1, 0.81 ± 0.17, 0.8 ± 0.1, and 0.85 ± 0.11 mmol/l at days 0, 1, 2, and 3, respectively). The mean total amount of Mg given, the mean total urine Mg excretion and the net Mg balance were significantly higher in the Mg group compared with the control group (58 ± 0.17 vs 11.3 ± 2.8 mmol, P > 0.001; 34.0 ± 2.7 vs 15.5 ± 3.8 mmol, P > 0.001; 25.6 ± 1.65 vs 5.2 ± 0.93 mmol, P > 0.001). In the Mg group, the numbers of Mg retainer patients were 24 patients on day 1, 21 on day 2 and nine patients on day 3. Mg nonretainer patients were six patients on day 1, nine on day 2 and 21 patients on day 3. Patients in the Mg group showed better haemodynamic stability and fewer ventricular arrhythmias.

Conclusion

Mg deficiency is common in ICU patients. Mg sulfate administered according to the above regimen is safe. Early treatment of Mg deficiency significantly increased the serum Mg level and provided a better magnesium, potassium and calcium balance, resulting in a shorter ICU stay.

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Salem, W. Magnesium deficiency in the surgical intensive care unit. Crit Care 11, P156 (2007). https://0-doi-org.brum.beds.ac.uk/10.1186/cc5316

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Keywords

  • Magnesium
  • Ventricular Arrhythmia
  • Magnesium Level
  • Serum Magnesium
  • Daily Measurement