All About Magnesium Sulfate

Introduction

Magnesium sulfate is a high risk, low frequency medication in EMS used for the control of both respiratory, cardiac, and OBGYN ailments. In this article, we will review the indications, pathophysiology, dosing information, specific Maryland protocol considerations, and research behind magnesium sulfate in order to better enhance provider knowledge. Because magnesium sulfate is such a low frequency medication, it is important to remain up to date and continue to learn more about why we use each medication.

Background & Pathophysiology

Magnesium is actually an electrolyte commonly found in the body and is used for the conduction of impulses and assisting in the regulation of the sodium-potassium pump. It is a cation - meaning that it is a positively charged ion inside the body. It is primarily found in the intracellular space and is responsible for assisting with the movement of potassium, sodium, calcium, and other ions throughout the body.

It is difficult to exhaustively state everywhere that magnesium is involved, as magnesium is used as a cofactor in a large variety of reactions, but we will cover the major roles pertinent to EMS care below.

Magnesium’s major role is in the prevention of calcium transferring in during contraction of smooth muscle cells. By preventing the movement of calcium, smooth muscle contractions occur at a reduced rate.

Magnesium is occasionally used as an OTC supplement for anxiety and sleep.

Cardiac: Magnesium is a natural calcium channel blocker and thus can be used in part to regulate ectopic and erratic sections of the heart, such as during torsades de pointes. Research has shown that it can be effective as a cardioprotective agent during times of ventricular hypertrophy or post-ROSC (Salaminia et al., 2018). It can reduce the risk of an arrhythmia by increasing the threshold that cardiac myocytes will fire, which in turn allows for control of irritable areas in the heart and helps maintain normal SA-node based pacemaking (Kaye & O’Sullivan, 2002). In addition, magnesium works as a peripheral vasodilator and reduces arterial spasm.

Respiratory: Magnesium can induce bronchodilation in the case of bronchoconstrictive conditions such as asthma. The exact mechanism is still unknown, but is likely related to calcium channel blockades in the respiratory smooth muscles.

OBGYN: During labor, magnesium sulfate’s calcium channel blocking effects can be used to reduce or halt contractions as a tocolytic. Because uterine contractions are smooth-muscle based, magnesium can relax those muscles.

CNS: Magnesium is a general CNS depressant in the doses we use it. It is used during eclampsia seizures in order to prevent cerebral edema, halt cerebral arterial spasm, and by halting seizure activity via its action on the NMDA receptors in the brain (Euser & Cipolla, 2009). This stops the action of glutamate - an excitatory neurotransmitter in the brain often responsible for seizures - by binding to their intended receptors and preventing the massive spike in neuronal activity that usually constitutes a seizure. It also works by halting the release of acetylcholine, a neurotransmitter responsible for muscular contractions, from receptors.

Typical Indications (EMS)

• Eclamptic Seizures

  • Dosing: 4g over 10 minutes in 50-100mL of LR bolus

• Torsades de Pointes

  • Dosing: 1-2 grams over 2 minutes bolus

  • Magnesium works in the use of torsades de pointes by inhibiting calcium movement which in turn inhibits contractions of the irritable ventricles. It also assists in regulation of conduction through the SA/AV nodes, which can help restore normal pacemaking to the heart.

• Refractory VT/VF

  • Dosing: 1-2 grams over 2 minutes bolus

  • As stated above, magnesium helps inhibit calcium transfer during times of ectopic ventricular pacemaking, such as torsades de pointes, VT, and VF.

• Respiratory (Bronchoconstriction)

  • Dosing: 1-2 grams over 10-20 minutes in 50-100mL LR

  • Magnesium assists with bronchodilation by acting on respiratory smooth muscle.

General Considerations

• Magnesium sulfate overdose is a significant risk when administering higher doses (2g+) or with rapid infusions.

  • Because magnesium is a calcium channel blocker, an overdose of magnesium can be treated with excess calcium.

  • Findings that may indicate magnesium overdose include CNS depression, depressed deep tendon reflexes (DTRs), respiratory depression, and hypotension.

  • Because magnesium inhibits muscular contraction by action on calcium, flaccid paralysis will occur in the case of overdose (Ajib, 2022).

  • Mainline treatment for overdose of magnesium is calcium chloride IVP 500mg-1gram.

References

Ajib, F. A. (2022, November 7). Magnesium Toxicity. StatPearls - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK554593/ Euser, A. G., & Cipolla, M. J. (2009). Magnesium Sulfate for the Treatment of Eclampsia. Stroke, 40(4), 1169–1175. https://doi.org/10.1161/strokeaha.108.527788 Hicks, M. A. (2022, May 8). Magnesium Sulfate. StatPearls - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK554553/ Kaye, P., & O’Sullivan, I. (2002). The role of magnesium in the emergency department. Emergency Medicine Journal, 19(4), 288–291. https://doi.org/10.1136/emj.19.4.288 Salaminia, S., Sayehmiri, F., Angha, P., Sayehmiri, K., & Motedayen, M. (2018). Evaluating the effect of magnesium supplementation and cardiac arrhythmias after acute coronary syndrome: a systematic review and meta-analysis. BMC Cardiovascular Disorders, 18(1). https://doi.org/10.1186/s12872-018-0857-6