Magnesium Prophylaxis for the Prevention of New-Onset Atrial Fibrillation in Critically Ill Patients

Inclusion Criteria 1. Age ≥18 years; 2. Admitted to an ICU with one or more of the following: 1. Non-invasive ventilation (including CPAP, Bipap and high flow oxygen (\>10L/min) or invasive mechanical ventilation with an expected duration \>24 hours for respiratory failure (hypercarbic or hypoxic) 2. Vasopressor or inotropic support with an expected duration of \>24 hours 3. Cardiac arrest 3. Continuous cardiac monitoring. Exclusion Criteria 1. Receiving ICU intervention (Non-invasive ventilation (including high flow nasal canula), invasive mechanical ventilation or inotropic support) for \>18 hours 2. Receiving IMV for airway protection only (for example, isolated head trauma) 3. Active atrial fibrillation at the time of enrolment 4. On oral or continuous infusion of Amiodarone 5. Unlikely to survive \>24 hours or palliative patients 6. Cardiac surgery patients 7. Patients requiring parenteral magnesium therapy (e.g. pre-eclampsia, asthma) 8. Patients receiving dialysis 9. Positive pregnancy test (females \<50 years old) 10. Previously enrolled in this trial 11. Treating physician refuses enrollment