American Society of Regional Anesthesia and Pain Medicine August 2018 - 39

Table 2: Summary of magnesium toxicity.
Serum Level

Symptoms

Signs

ECG findings

4-6 mEq/L

Nausea, vomiting, lethargy,
and headache

Diminish DTRs and
hypotension because of
vasodilation

6-10 mEq/L

Nausea, vomiting, lethargy,
and headache

Absent DTRs, bradycardia,
and hypotension

Increased QRS duration
and prolongation of PR and
QT intervals

Coma, paralysis,
respiratory failure, and
cardiac arrest

Complete heart block

>10 mEq/L

Other concerns
Associated with increased
potassium and decreased
calcium levels
Inhibition PTH release
causing systemic
decreased calcium levels

Abbreviations: DTRs, deep tendon reflexes; ECG, electrocardiogram; PTH, parathyroid hormone

a 2 g IV bolus of magnesium improves peak expiratory flow rates
and forced expiratory volumes in acute asthma attacks.17
Although magnesium has numerous benefits and a large
therapeutic window, its use is not entirely without risk: a summary
of magnesium toxicity is presented in Table 2. Consequently,
close monitoring is required for all patients receiving therapeutic
magnesium, and administration must be stopped with the
development of any signs or symptoms of hypermagnesemia.
Additionally, IV calcium acts as an antagonist to magnesium and
should be administered immediately if patients experience sequelae
of hypermagnesemia.
Therapeutic magnesium administration should be used with
caution or avoided in certain patient populations. Given
magnesium's propensity to cause muscle weakness and
electrocardiogram changes, it is best avoided in patients with
pre-existing atrioventricular block and those with chronic
neuromuscular diseases, such as myasthenia gravis. Similarly,
because magnesium homeostasis is maintained through renal
excretion, patients who have renal impairment are at higher risk
for accumulating toxic levels. Notably, patients with end-stage
renal failure may require dialysis to reduce magnesium levels.
Conversely, patients with normal renal function or moderate
renal impairment may receive fluids and loop diuretics to hasten
reduction of magnesium levels.
CONCLUSION
The cost of the opioid epidemic in the United States is
astronomically high on patients, families, and communities. Shipton
et al18 reported that the economic liability of opioid misuse in the
United States is projected to exceed $78 billion a year. This, in
combination with recent drug shortages in the operating room, has
resulted in increased demand for anesthesiologists to seek out
nonopiate analgesic strategies in the perioperative period, in which
magnesium plays an important role.19

Magnesium has a long history of perioperative use for numerous
indications. A definitive analgesic dose should be the product
of consideration of patient comorbidities, type of surgery, and
anesthetic requirements. Based on recent literature, a loading dose
of magnesium of 30-50 mg/kg followed by an infusion of 8-15 mg/
kg/hr can be a powerful tool in an anesthesiologist's antinociceptive
arsenal. In the era of enhanced recovery after surgery and opioid
abuse epidemics, the time has never been better to incorporate this
potent analgesic into our daily perioperative care.
REFERENCES
1.

Begon S, Pickering G, Eschalier A, Dubray C. Magnesium increases morphine
analgesic effect in different experimental models of pain. Anesthesiology.
2002;96:627-632.

2.

McCarthy RJ, Kroin JS, Tuman KJ, Penn RD, Ivankovich AD. Antinociceptive
potentiation and attenuation of tolerance by intrathecal co-infusion of
magnesium sulfate and morphine in rats. Anesth Analg. 1998;86:830-836.

3.

Ko SH, Lim HR, Kim DC, Han YJ, Choe H, Song HS. Magnesium sulfate does not
reduce postoperative analgesic requirements. Anesthesiology. 2001;95:640-646.

4.

Wilder-Smith CH, Knopfli R, Wilder-Smith OHG. Perioperative magnesium
infusion and postoperative pain. Acta Anaesthesiol Scand. 1997;41:1023-1027.

5.

O'Flaherty J, Lin C. Does ketamine or magnesium affect posttonsillectomy pain
in children? Pediatr Anaesth. 2003;13:413-421.

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Kara H, S¸ahin N, Ulusan V, Aydog˘du T. Magnesium infusion reduces perioperative
pain. Eur J Anaesthesiol. 2002;19:52-56.

7.

Levaux Ch, Bonhomme V, Dewandre PY, Brichant JF, Hans P. Effect of intraoperative magnesium sulphate on pain relief and patient comfort after major
lumbar orthopaedic surgery. Anaesthesia. 2003;58:131-135.

8.

Elsersy H, Metyas M, Elfeky H, Hassan A. Intraoperative magnesium sulphate
decreases agitation and pain in patients undergoing functional endoscopic
surgery. Eur J Anaesthesiol. 2017;34:658-664.

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Song J, Lee Y, Yoon K, Park S, Shim Y. Magnesium sulfate prevents remifentanilinduced postoperative hyperalgesia in patients undergoing thyroidectomy.
Anesth Analg. 2011;113(2):390-397.

10. Rodríguez-Rubio L, Nava E, del Pozo J, Jordán J. Influence of the perioperative
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2018

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