THE LACK OF EFFECT OF ROUTINE MAGNESIUM ADMINISTRATION ON RESPIRATORY-FUNCTION IN MECHANICALLY VENTILATED PATIENTS

Study objective: We wished to determine if magnesium infusion would improve respiratory muscle function in long-term ventilated patients even in the absence of hypomagnesemia. Design: Prospective study of mechanically ventilated patients using a double-blind crossover design. Setting: A combined medical-surgical ICU of a university teaching hospital. Patients: Twenty-one separate admissions to the ICU in 20 patients were studied. Patients who were selected had been intubated and mechanically ventilated for at least 6 days with the admitting diagnosis of respiratory failure. Interventions: Twelve patients received 6 g MgSO4 intravenous (IV) infusion over 16 h on day 1 followed by placebo infusion on day 2. Nine patients received placebo on day 1 followed by MgSO4 (6 g IV) on day 2. Measurements and main results: We measured vital capacity (VC), maximal inspiratory pressure (PImax) and maximal expiratory pressure (PEmax) in all patients. There were no significant differences in Pimax (37 +/- 14 vs 42 +/- 20 cm H2O), PEmax (59 +/- 32 vs 61 +/- 38 cm H2O), and VC (850 +/- 460 vs 960 +/- 490 ml) comparing values before and after magnesium infusion. We could not find a subgroup of patients with a marked improvement in PImax or PEmax. Conclusions: In patients requiring mechanical ventilation for respiratory failure, magnesium infusion is not associated with increased respiratory muscle strength. Although a trial of MgSO4 administration may be considered for patients with difficulty weaning from mechanical ventilation, it is unlikely to result in clinical improvement.