1. ROLE OF MAGNESIUM,
ITS DISORDER &
MANAGEMENT.
Dr. Arjun chhetri, Resident (NGMC)

2. magnesium
 2nd abundant intracellular cation.
 Serve as a cofactor >300 enzyme recn i.e. involve ATP.
 Proper functioning of the Na+-K+ exchange pump that
generates the electrical gradient across cell membranes.
 regulates the movement of calcium into smooth muscle
cells (maintenance of cardiac contractile strength and
peripheral vascular tone)

3. Magnesium balance
 The average-sized adult contains approximately 24 g of
Mg. (over half is located in bone, < 1% is located in
plasma).

4. Serum Magnesium
 Serum is favored over plasma for magnesium assays.
Ionized Magnesium
 About 67% of the Mg in plasma is ionized, remaining
33% bound to plasma protein(19%), chelated (14%).
 Spectrophotometry measures all three fractions.

5. Urinary Magnesium
 Small quantities of magnesium are excreted in the urine.
 When Mg intake is deficient, the kidneys conserve Mg
and urinary Mg excretion falls to negligible levels.

6. Reference Ranges for
Magnesium

7. MAGNESIUM DEFICIENCY
 Hypomagnesemia is reported in as many as 65% of
patients in ICU’s.
 Mg depletion may not be accompanied by
hypomagnesemia, incidence probably higher.
 magnesium depletion has been described as :
“the most underdiagnosed electrolyte abnormality in
current medical practice”

8. Predisposing Conditions

9. Diuretic Therapy
 Diuretics are the leading cause of Mg deficiency.
 Urinary Mg excretion is most pronounced with the loop
diuretics (furosemide and ethacrynic acid).
 reported in 50% of patients receiving chronic therapy
with furosemide.
 thiazide diuretics show a similar tendency for
magnesium depletion, but only in elderly patients .
 Mg depletion does not occur with “potassium-sparing”
diuretics

10. Antibiotic Therapy
 Aminoglycosides, amphotericin and pentamidine.
 The aminoglycosides block Mg reabsorption in the
ascending loop of Henley.
 Hypomagnesemia has been reported in 30% of patients
receiving aminoglycosides therapy

11. Other Drugs
 case reports- prolonged use of PPI (14 days to 13
years) can be associated with severe hypomagnesemia.
 Other drugs digitalis, epinephrine, and the
chemotherapeutic agents cisplatin and cyclosporine.

12. Alcohol
 Hypomagnesemia is reported in 30% of hospital
admissions for alcohol abuse, and in 85% of admissions
for delirium tremens.
 There is an association between magnesium deficiency
and thiamine deficiency
(required for the transformation of thiamine into
thiamine pyrophosphate)

13. Secretory Diarrhea
 Secretions from the lower GI tract are rich in magnesium
(10–14 mEq/L).
 Upper GI tract secretions are not rich in magnesium (1–
2 mEq/L).

14. Diabetes Mellitus
 common in insulin-dependent diabetic patients, probably
as a result of urinary Mg losses that accompany
glycosuria.
 reported in only 7% of admissions for diabetic
ketoacidosis.
 incidence increases to 50% over the first 12 hours after
admission.

15. Acute Myocardial Infarction
 Hypomagnesemia is reported in as many as 80% of
patients with acute myocardial infarction.
 The mechanism is unclear.

16. Clinical Manifestations
 no specific clinical manifestations of magnesium
deficiency
 often accompanied by depletion of potassium,
phosphate, and calcium.
HYPOKALEMIA: Hypokalemia is reported in 40% of cases
of magnesium depletion.
 hypokalemia that accompanies magnesium depletion
can be refractory to potassium replacement therapy.
 magnesium replacement is often necessary before the
hypokalemia can be corrected

17. CONTD…
HYPOCALCEMIA: can cause hypocalcemia as a result of
impaired parathormone release.
 Hypocalcemia from magnesium depletion is difficult to
correct unless magnesium deficits are corrected.
HYPOPHOSPHATEMIA: Phosphate depletion is a cause
rather than effect of magnesium depletion.
 The mechanism is enhanced renal magnesium
excretion.

18. CONTD…
Arrhythmias
 Magnesium depletion will depolarize cardiac cells and
promote tachyarrhythmia's.
 magnesium deficiency will magnify the digitalis effect
and promote digitalis cardio toxicity.
 IV magnesium can suppress digitalis-toxic arrhythmias
 IV magnesium can also abolish refractory arrhythmias
(i.e., unresponsive to traditional antiarrhythmic agents)
in the absence of hypomagnesemia.

19. CONTD…
 One of the serious arrhythmias associated with
magnesium depletion is torsade de pointes
 Hypomagnesemia is associated with an increased incidence
of atrial fibrillation.

20. CONTD…
Neurologic Findings
 Altered mentation, generalized seizures, tremors, and
hyperreflexia. (All are uncommon, nonspecific, and have
little diagnostic value).
 The clinical presentation is characterized by ataxia,
slurred speech, metabolic acidosis, excessive salivation,
diffuse muscle spasms, generalized seizures.
 The clinical features are often brought out by loud
noises or bodily contact, and thus the term reactive CNS
magnesium deficiency.

21. Diagnosis
 serum Mg level is an insensitive marker of magnesium
depletion.
 When magnesium depletion is due to nonrenal factors
(e.g., diarrhea), the urinary magnesium excretion is a
more sensitive test for magnesium depletion.

22. CONTD…
Renal Magnesium Retention Test

23. Magnesium Replacement
 Oral and Parenteral Magnesium Preparations

24. CONTD…
 The following magnesium replacement protocols are
recommended for patients with normal renal function
Mild, Asymptomatic Hypomagnesemia
 The following guidelines can be used for a serum Mg of
1–1.4 mEq/L with no apparent complications :
1. Assume a total magnesium deficit of 1–2 mEq/kg.
2. Because 50% of the infused magnesium can be lost in
the urine, assume that the total magnesium requirement
is twice the magnesium deficit.
3. Replace 1 mEq/kg for the first 24 hours, and 0.5 mEq/kg
daily for the next 3–5 days.

25. CONTD…
Moderate Hypomagnesemia
 The following protocol is recommended for a serum Mg
<1 mEq/L, or for a low serum Mg that is accompanied by
other electrolyte abnormalities:
1. Add 6 g MgSO4 (48 mEq of Mg) to 250 or 500 mL
isotonic saline and infuse over 3 hours.
2. Follow with 5 g MgSO4 (40 mEq of Mg) in 250 or 500
mL isotonic saline infused over the next 6 hours.
3. Continue with 5 g MgSO4 every 12 hours (by
continuous infusion) for the next 5 days.

26. CONTD…
Life-Threatening Hypomagnesemia
 The following is recommended for hypomagnesemia
associated with serious cardiac arrhythmias (e.g.,
torsade de pointes) or generalized seizures:
1. Infuse 2 g MgSO4 (16 mEq of Mg) intravenously over 2–
5 minutes.
2. Follow with 5 g MgSO4 (40 mEq of Mg) in 250 or 500
mL isotonic saline infused over the next 6 hours.
3. Continue with 5 g MgSO4 every 12 hours (by
continuous infusion) for the next 5 days.

27. Monitoring Replacement
Therapy
 Serum Mg levels will rise after the initial magnesium
bolus, but will begin to fall after 15 minutes.
 Serum Mg levels may normalize after 1 to 2 days, but it
will take several days to replenish the total body
magnesium stores.
 The magnesium retention test can be valuable for
identifying the end-point of potassium replacement
therapy.

28. Anesthetic Considerations
 no specific anesthetic Anesthetic Considerations
 Isolated hypomagnesemia should be corrected prior to
elective procedures because of its potential for causing
cardiac arrhythmias.
 magnesium appears to have intrinsic antiarrhythmic
properties & cerebral protective effects (administered prior
to cardiopulmonary bypass).

29. Eclampsia & magnesium
Mild preeclampsia-
Prophylactic use is controversial.
Severe pre-eclampsia-
 When prophylactically used 50% reduction in
progression to eclampsia but with no neonatal or
maternal mortality benefit.
 25% of magnesium-treated women experienced side
effects, mainly flushing

30. CONTD…
Eclampsia-
 Clear benefit on prevention of seizure recurrence as
compared to diazepam and phenytoin.
 Recommended dose being 4-6 gms IV over 20-30 mins
f/b 1-2 gms/h or 4 gms in each buttock every 4 hr
continued for at least 24 hrs after delivery.

31. HYPERMAGNESEMIA
 serum Mg >2 mEq/L
 Nearly always due to excessive intake (magnesium-containing
antacids or laxatives) renal impairment (GFR < 30 mL/min).
 Iatrogenic hypermagnesemia during magnesium sulfate
therapy for gestational hypertension in the mother as well as
the fetus.
 Rear causes include adrenal insufficiency, hypothyroidism,
rhabdomyolysis, and lithium administration.

32. Predisposing Conditions
 Renal Insufficiency
 Hemolysis: The Mg concentration in erythrocytes is
approximately three times greater than in serum.
 serum Mg is expected to rise by 0.1 mEq/L for every 250
mL of erythrocytes that lyse completely , so
hypermagnesemia is expected only with massive
hemolysis.

33. Clinical Features
 The clinical consequences of progressive
hypermagnesemia
 Magnesium has been described as nature’s physiologic
calcium blocker
 Most of the cardiovascular depression is the result of
cardiac conduction delays.

34. Contd…
 Symptomatic hypermagnesemia typically presents with
neurological, neuromuscular, or cardiac manifestations.
 Hyporeflexia, sedation, and skeletal muscle weakness are
characteristic features.
 impair the release of acetylcholine and decreases motor end-
plate sensitivity to acetylcholine in muscle.
 Marked hypermagnesemia can lead to respiratory arrest.

35. Management
 All sources of magnesium intake should be stopped.
 Intravenous calcium (1 g calcium gluconate) can temporarily
antagonize most of the effects of hypermagnesemia.
 A loop diuretic along with an infusion of ½-NS in 5% dextrose
enhances urinary magnesium excretion.
 Hemodialysis is the treatment of choice for severe
hypermagnesemia.

36. Anesthetic Considerations
 Requires close monitoring of the ECG, blood pressure, and
neuromuscular function.
 Potentiation of the vasodilating and negative inotropic
properties of anesthetics should be expected.
 Dosages of NMBAs should be reduced by 25–50%.
 Serial measurements of [Ca2+] and [Mg2+] may be useful.

37. Magnesium & Its others uses
Preterm birth and fetal neuroprotection
 used as a tocolytic agent, attenuates uterine
contractility in vivo and in vitro.
 Studies have shown Iv magnesium to reduce the risk of
cerebral palsy in surviving preterm babies.
 Antenatal administration may be considered because
there is some evidence showing its neuroprotective
effects in preterm neonates.

38. Contd…
Magnesium and Pheochromocytoma
 Care of patients during surgical removal of
pheochromocytoma poses a significant anesthetic
challenge.
 Standard preoperative treatment includes
pharmacologic stabilization by - and β-adrenergic
antagonists.
 Several case reports have described the successful use
of magnesium during pheochromocytoma crisis.

39. Contd…
 MOA: May stabilize hemodynamic by inhibition of
catecholamine release from the adrenal medulla and
peripheral adrenergic nerve endings
 direct blockade of catecholamine receptors and
vasodilation.
 antiarrhythmic properties related to L-type calcium
channel antagonism.

40. Contd…
Magnesium and Asthma or Chronic Obstructive Pulmonary
Disease
magnesium-induced bronchodilation may be mediated by
several pathways:
 attenuation of calcium-induced muscle contractions,
 inhibition of cholinergic neuromuscular transmission,
 Anti-inflammatory activity.

41. Contd…
Magnesium in tetanus
 Use of magnesium reduce the need for mechanical
ventilation, minimize sedation, minimize sympathetic
overactivity associated with tetanus.
 MgSO4 in the dose – 5gm iv loading dose f/b 2-3gm/hr
via infusion. Therapy guided by patellar tendon reflex.

42. Magnesium and Side Effects
 burning sensation or
pain on injection
 induce agitation
 drowsiness
 nausea
 Headache
 Dizziness
 muscle weakness
 hypotension and
 bradycardia.
 In eclampsia, approximately
25% of pts. flushing occurs.
 Increases the risk of
postpartum hemorrhage and
respiratory depression.
 neonatal lethargy,
hypotension, and rarely
respiratory depression after
prolonged administration
(more than 48 h).

43. THANK YOU
 REFERENCES
 PAUL MORINO ICU
 MORGAN CLINICAL ANESTHESIOLOGY