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From Baby Miller...Ch. Obstetrics
Magnesium is effective in pregnant women with pre-eclampsia by "decreasing the irritability of the CNS"??, which decreases the likelihood of seizures.
Magnesium also
1. decreases hyperactivity at the NMJ by presumably decreasing the presynaptic release of Ach
2. decrases the sensitivity of postjunctional membranes to Ach
3. Relaxes uterine and vascular smooth muscle, increasing uterine blood flow
Therapeutic levels to prevent seizures are between 4-6 mEq/L. Loss of DTR are a sign of impending toxicity
Levels higher than 6 mEq/L can lead to
a) Severe skeletal muscle weakness-->paralysis
b) Hypoventilation, lethargy, somnolence
c) Prolonged PR and QT intervals-->Cardiac arrest
Antidote for Mg toxicity-->IV Calcium 5-10 mEq, saline, diuretics
Magnesium is excreted by the kidneys, so it has to be titrated carefully in patients with impaired renal function, as in pregnant pts with preeclampsia.
Asides:
-Since Mg decreases the release of presynaptic Ach at the NMJ, neuromuscular blockers can have longer lasting effects on pts on Mg.
-Baby Miller als states Mg can enhance the effects of opioids and sedatives
-Preeclampsia may be associted with decreases in plasma cholinesterase potentiating the effects of succinylcholine. Barash states that ?magnesium decreases the release of potassium in response to succinylcholine?
Magnesium is effective in pregnant women with pre-eclampsia by "decreasing the irritability of the CNS"??, which decreases the likelihood of seizures.
Magnesium also
1. decreases hyperactivity at the NMJ by presumably decreasing the presynaptic release of Ach
2. decrases the sensitivity of postjunctional membranes to Ach
3. Relaxes uterine and vascular smooth muscle, increasing uterine blood flow
Therapeutic levels to prevent seizures are between 4-6 mEq/L. Loss of DTR are a sign of impending toxicity
Levels higher than 6 mEq/L can lead to
a) Severe skeletal muscle weakness-->paralysis
b) Hypoventilation, lethargy, somnolence
c) Prolonged PR and QT intervals-->Cardiac arrest
Antidote for Mg toxicity-->IV Calcium 5-10 mEq, saline, diuretics
Magnesium is excreted by the kidneys, so it has to be titrated carefully in patients with impaired renal function, as in pregnant pts with preeclampsia.
Asides:
-Since Mg decreases the release of presynaptic Ach at the NMJ, neuromuscular blockers can have longer lasting effects on pts on Mg.
-Baby Miller als states Mg can enhance the effects of opioids and sedatives
-Preeclampsia may be associted with decreases in plasma cholinesterase potentiating the effects of succinylcholine. Barash states that ?magnesium decreases the release of potassium in response to succinylcholine?
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