Clinician preference instrumental variable analysis of the effectiveness of magnesium supplementation for atrial fibrillation prophylaxis in critical care

Abstract

Atrial fibrillation is a frequently encountered condition in critical illness and causes adverse effects including haemodynamic decompensation, stroke and prolonged hospital stay. It is a common practice in critical care to supplement serum magnesium for the purpose of preventing episodes of atrial fibrillation. However, no randomised studies support this practice in the non-cardiac surgery critical care population, and the effectiveness of magnesium supplementation is unclear. We sought to investigate the effectiveness of magnesium supplementation in preventing the onset of atrial fibrillation in a mixed critical care population. We conducted a single centre retrospective observational study of adult critical care patients. We utilised a natural experiment design, using the supplementation preference of the bedside critical care nurse as an instrumental variable. Using routinely collected electronic patient data, magnesium supplementation opportunities were defined and linked to the bedside nurse. Nurse preference for administering magnesium was obtained using multilevel modelling. The results were used to define "liberal" and "restrictive" supplementation groups, which were inputted into an instrumental variable regression to obtain an estimate of the effect of magnesium supplementation. 9114 magnesium supplementation opportunities were analysed, representing 2137 critical care admissions for 1914 patients. There was significant variation in magnesium supplementation practices attributable to the individual nurse, after accounting for covariates. The instrumental variable analysis showed magnesium supplementation was associated with a 3% decreased relative risk of experiencing an atrial fibrillation event (95% CI − 0.06 to − 0.004, p = 0.03). This study supports the strategy of routine supplementation, but further work is required to identify optimal serum magnesium targets for atrial fibrillation prophylaxis.

Magnesium prophylaxis of new-onset atrial fibrillation: A systematic review and meta-analysis

“…In a network meta-analysis among post general thoracic surgery patients, magnesium therapy was effective in prevention of post-operative atrial fibrillation (OR 0.35; 0.16 to 0.74 95% CI) compared to placebo/usual care with no obvious side effects [ 58 ]. Wilson et al performed an instrument variable analysis using the supplementation preference of bedside critical care nurses, and showed liberal magnesium supplementation was associated with a 3% decreased relative risk of experiencing an AF event when compared to restrictive supplementation [ 22 ].…”

“…Prophylaxis of NOAF in the ICU has potential to improve patient outcomes with decreased hemodynamic instability, exposure to medications with potential side effects, uncomfortable electrical cardioversion attempts, decreased risk of stroke, heart failure and mortality, and cost-savings [ 19 ]. Few prophylactic interventions for NOAF have been studied in a critical care population, with two small observational studies in ICU patients suggesting that hydrocortisone use was associated with a decreased risk of developing NOAF in the acute phase of critical illness [ 20 , 21 ], and one study comparing liberal versus restrictive magnesium supplementation for prevention of atrial fibrillation [ 22 ]. This is in contrast to cardiac surgery populations, where pharmacologic and surgical prophylaxis against NOAF has been well studied and has been successful in reducing the incidence of AF, as well as postoperative morbidity and mortality [ 23 ].…”