title: Outcome-based justification for implementing new point-of-care tests: there is no difference between magnesium replacement based on ionized magnesium and total magnesium as a predictor of development of arrhythmias in the postoperative cardiac surgical patient.
abstract: OBJECTIVE
  To 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.
  
  
  METHODS
  A prospective randomized trial.
  
  
  METHODS
  Cardiothoracic surgical intensive care unit of a university hospital.
  
  
  METHODS
  One 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.
  
  
  RESULTS
  Eighty-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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: Hospital of the University of Pennsylvania, Philadelphia, USA.
authors.forename: H A
authors.initials: HA
authors.lastname: Steinberger
authors.forename: C W
authors.initials: CW
authors.lastname: Hanson
mesh_terms: D000368:Aged; D001145:Arrhythmias, Cardiac / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control*; D015415:Biomarkers; D002315:Cardiopulmonary Bypass; D005260:Female; D006785:Hospitals, University; D006801:Humans; D007591:Joint Commission on Accreditation of Healthcare Organizations; D008274:Magnesium / Q000097:blood* / Q000627:therapeutic use; D008297:Male; D017063:Outcome Assessment, Health Care; D015143:Philadelphia / Q000453:epidemiology; D019095:Point-of-Care Systems; D011182:Postoperative Care; D011183:Postoperative Complications / Q000517:prevention & control; D011446:Prospective Studies; D013673:Technology Assessment, Biomedical / Q000379:methods*