• H A Steinberger and C W Hanson.
• Hospital of the University of Pennsylvania, Philadelphia, USA.
• Clin Lab Manage Rev. 1998 Mar 1; 12 (2): 87-90.

ObjectiveTo determine whether introducing a new laboratory test, ionized magnesium (iMg++), would affect outcome, where outcome was defined as the rate of arrhythmias in a population of postoperative cardiopulmonary bypass (CPB) patients.DesignA prospective randomized trial.SettingCardiothoracic surgical intensive care unit of a university hospital.PatientsOne hundred fifty consecutive post-CPB patients with randomized to two groups, one of which received routine reporting of iMg++ levels on all postoperative electrolyte requests while the other had access to total magnesium (tMg++) levels on demand and no access to iMg++ levels. Groups were compared for rate of arrhythmias, total amount of magnesium repleted, and demographics.Measurements And Main ResultsEighty-five patients were randomized to the tMg++ group and 65 to the iMg++ group. The two groups did not differ in the rate of arrhythmias (chi-square test): 13/85 (15%) of the tMg++ patients and 12/65 (18%) of the iMg++ patients developed an arrhythmia. The groups also did not differ in the amount of magnesium sulfate (MgSO4) administered (2 tailed t-test): tMg++ patients received 1.5 +/- 0.15 (SEM) gm of MgSO4, whereas iMg++ patients received 1.3 +/- 0.15 gm.ConclusionThe study does not support the hypothesis that magnesium repletion titrated to iMg++ reduces arrhythmia development in post-CPB patients. The lack of a difference in the amount of magnesium replacement between the two groups suggests that tMg++ level is a reasonable indicator of iMg++ level. Routine measurement of iMg++ does not, therefore, appear to have advantages over tMg++ in the postoperative management of CPB patients.

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