In this episode, I’ll discuss whether routine magnesium supplementation of ICU patients reduces tachyarrhythmia incidence.
It is routine practice to give ICU patients supplemental IV magnesium if their plasma level is below the normal lab range, and this practice is hoped to reduce the incidence of new onset atrial fibrillation or other tacchyarrhymias in such patients.
Because previous observational studies looking at the effects of magnesium supplementation are thought to have methodological shortcomings that introduce confounding and bias, a group of authors published in JAMA a quasi-experimental study that they felt could plausibly allow for casual inference.
Data from over 170,000 patients in 93 ICUs were included in the study. The authors used what they call a fuzzy regression discontinuity design where patients just over either side of the eligibility cutoff for magnesium supplementation were compared with regard to the study outcomes. This comparison was performed across a range of treatment cutoffs currently in use, from 1.6 mg/dL to 2 mg/dL.
The primary outcome was ventricular or supraventricular tachyarrhythmia in the 24 hours after magnesium testing. Secondary outcomes were the occurrence of hypotension or death.
Unfortunately, there was no evidence of an effect of magnesium supplementation on the occurrence of atrial fibrillation or other tachyarrhythmia. The lack of difference held over every cutoff level evaluated. Likewise, there was no association with hypotension or death for any group studied.
The authors concluded:
In this nonrandomized clinical trial, routine supplementation of magnesium with currently used doses and treatment thresholds was not associated with beneficial effects for individuals with serum magnesium values close to those cutoffs.
While it looks like magnesium supplementation is not worthwhile in a general ICU population based on this study, I am not confident that the study design and strength of the evidence will be enough to convince clinicians to completely discontinue the practice of giving ICU patients with mildly low magnesium levels supplementation.
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