American Society of Regional Anesthesia and Pain Medicine August 2018 - 37
"Oh Mg!" Magnesium: A Powerful Tool in the Perioperative Setting
A
lthough a little bag of magnesium
sulfate might not look like
much, the divalent cation
possesses numerous attributes that
have served anesthesiologists well
for many decades. Magnesium is
a cofactor to ATP production, aids
in ion transportation, competitively
antagonizes calcium release, inhibits
catecholamine release, and antagonizes
N-methyl-D-aspartate (NMDA)
receptors. Although its analgesic
properties may have been overlooked
for newer and more sophisticated
drugs, magnesium has resurfaced in
the era of bundled payments, enhanced
recovery pathways, and multimodal
analgesic plans.
Renuka M. George, MD
Assistant Professor
Department of Anesthesia and
Perioperative Medicine
Over time, magnesium has been used
for a variety of perioperative applications. It was first examined
as a potential induction agent in the early 1900s, but its use
was unsuccessful because of poor bioavailability and its limited
capacity to cross the blood-brain barrier. However, increased
interest in the 1980s focused on magnesium's ability to antagonize
NMDA receptors. Since then, numerous studies, reviews, and
meta-analyses have attempted to clarify the role of perioperative
magnesium.
Jackson M. Condrey, MD
Regional Anesthesia Fellow
Department of Anesthesia and
Perioperative Medicine
Sylvia H. Wilson, MD
Associate Professor
Department of Anesthesia and
Perioperative Medicine
Medical University of South Carolina
Charleston, South Carolina
In a separate study of hysterectomy patients, subjects received
magnesium (200 mg bolus on induction and 200 mg/hr infusion
for 5 hours) or placebo and were followed for 48 hours.4
The magnesium group demonstrated higher pain scores 3
hours following their surgical procedure yet decreased opioid
consumption 1 hour following surgery, but no other differences
were noted between groups. In children undergoing tonsillectomy
and administered placebo, ketamine, magnesium (30 mg/kg
bolus intraoperatively), or
ketamine plus magnesium,
significant differences
in pain scores were not
noted between groups.5
With all these studies, the
wide variety of doses and
baseline pain medications,
as well as numerous other
confounding factors, may
have contributed to the
negative findings.
"Although its analgesic properties may
have been overlooked for newer and
more sophisticated drugs, magnesium
has resurfaced in the era of bundled
payments, enhanced recovery pathways,
and multimodal analgesic plans."
ANALGESIA
Both animal and clinical
studies have highlighted
magnesium's antinociceptive
effects. Its proposed
mechanism of action
includes competitive and
noncompetitive NMDA
antagonism of hippocampal
presynaptic calcium channels
that regulate aspartate
and glutamate. Both pathways are thought to contribute to the
prevention of central sensitization. In animal models, magnesium
has inhibited hyperalgesia, amplified the analgesic effects of lowdose morphine, and delayed morphine tolerance.1,2
Several studies, reviews, and meta-analyses have examined
intravenous (IV) magnesium in the intraoperative setting with
conflicting results. In patients undergoing abdominal hysterectomy
and randomized to magnesium (50 mg/kg bolus with 15 mg/kg/
hr infusion for 6 hours) or saline, postoperative pain scores and
analgesic demand boluses did not differ between the groups.3
However, all the patients had patient-controlled epidural anesthesia.
Alternatively, numerous clinical studies have demonstrated the
antinociceptive effects of magnesium; however, dosing strategies
were highly variable. Postoperative analgesia was improved after
abdominal hysterectomy with an initial bolus of IV magnesium
(30 mg/kg) followed by an infusion (0.5 g/hr).6 Likewise, an IV
magnesium bolus (50 mg/kg) at induction improved pain and
decreased opioid consumption following lumbar spine surgery.7
In addition to decreased opioid consumption and shorter recovery
room stays, an IV magnesium bolus (30 mg/kg) within an hour
of induction followed by an infusion (9 mg/kg/hr) decreased
postoperative agitation following functional endoscopic sinus
surgery.8 The authors attributed the findings to improved pain
American Society of Regional Anesthesia and Pain Medicine
2018
37
Table of Contents for the Digital Edition of American Society of Regional Anesthesia and Pain Medicine August 2018
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