UMEM Educational Pearls

Magnesium is known to relax smooth muscles.  Interestingly, there is also some literature using it as part of Rapid Sequence Intubation (RSI) pre-treatment in general, in hopes that this or other mechanisms might allow it to improve intubating conditions.  Zouche et al recently published an RCT looking at giving IV magnesium as part of RSI pretreatment in cases where neuromuscular blockade (NMB) is not going to be given (e.g. scenarios where it is contraindicated).  IV Magnesium Sulfate, 50 mg/kg in 100 mL of saline given 15 minutes before induction, significantly improved intubating conditions in those getting sedation but not NMB (95% vs 39%).  

In 2013, Park et al did an RCT giving magnesium to all RSIs, even with the use of rocuronium in those patients, arguing that magnesium is also known to potentiate the effects of non-depolarizing NMB agents.  They also found better intubating conditions in the magnesium patients.

In both trials, magnesium was associated with lower heart rates and less hypertension in the peri-intubation and immediate post-intubation periods (of note: high dose magnesium is known to be associated with lower blood pressures, and can induce overt hypotension).  Neither study was really powered for more important measures like first pass success, mortality, or important side effects like peri-intubation hypotension.

Bottom Line: These are two small trials, and while more abundant literature should probably be obtained before we change our practice, one could consider giving magnesium sulfate, 50 mg/kg in 100 mL saline, prior to intubation in an attempt to improve intubating conditions.  In my opinion, this is probably worth considering in the rare circumstance that your patient has a true contraindication to neuromuscular blockade, but I probably wouldn't start doing this in standard RSI where you're going to be giving NMB until more literature confirms the safety of this approach.  Also, I would avoid this in situations where the patient is already hypotensive or at high risk of peri-intubation hypotension.  This may be worth considering in the very rare patient you're not necessarily going to give NMB to right away (maybe awake fiberoptic intubations?) who are also very low risk for hypotension.

References

Imen Zouche, Wassim Guermazi, Faiza Grati, Mohamed Omrane, Salma Ketata, Hichem Cheikhrouhou, Intravenous magnesium sulfate improves orotracheal intubation conditions: A randomized clinical trial, Trends in Anaesthesia and Critical Care, Volume 57, 2024, 101371, ISSN 2210-8440, https://doi.org/10.1016/j.tacc.2024.101371 (https://www.sciencedirect.com/science/article/pii/S221084402400042X)

Park SJ, Cho YJ, Oh JH, Hwang JW, Do SH, Na HS. Pretreatment of magnesium sulphate improves intubating conditions of rapid sequence tracheal intubation using alfentanil, propofol, and rocuronium - a randomized trial. Korean J Anesthesiol. 2013 Sep;65(3):221-7. doi: 10.4097/kjae.2013.65.3.221. Epub 2013 Sep 25. PMID: 24101956; PMCID: PMC3790033.