Medical and Surgical Complications in Pregnancy
Earliest feature of Magnesium toxicity? (AIPG 2011)
|D|| Loss of deep tendon reflexes|
Loss of deep tendon reflexes.
1. Magnesium sulfate is the treatment of choice for the prevention and treatment of eclamptic seizures.
2. It reduces motor end plate sensitivity to acetyl choline.
3. It has no detrimental effects on neonate within therapeutic level.
4. The therapeutic level of serum magnesium is 4—7 mEq/L.
5. It induces cerebral vasodilatation, dilates uterine arteries increases production of endothelial prostacyclin and inhibits platelet activation.
6. Magnesium may prevent seizures by interacting with N-methyl-D-aspartate (NMDA) receptors in the central nervous system.
7. Repeat injections are given only if
a. Knee jerks are present,
b. Urine output is > 30ml/hour, and
c. Respiration rate is > 12/min.
8. Eclamptic convulsions are almost always prevented by maintaining plasma magnesium levels between 4—7 mEq/L (4.8 tp 8.4 mg/dl, or 2.0-3.5 mmol/L).
9. Loss of DTRs serves as the earliest warning sign of impending magnesium toxicity, because a further increase leads to respiratory depression.
a. Patellar reflex disappears when magnesium level reaches 10 mEq/L (12 mg/dl), presumably because of curariform action.
b. When magnesium levels go > 10 mEq/L, respiratory depression develops.
c. At levels = 12 mEq/L, respiratory paralysis and arrest follows.
a. with calcium gluconate 1 gm IV and with-holding magnesium sulphate reverses mild to moderate respiratory depression.
b. Usually magnesium sulphate is otherwise discontinued 24 hours delivery.
Regimen Loading dose Maintenance dose
Pritchard 4 gm IV over 3-4 min, 10 mg deep IM 5 gm IM in alternate buttock
Zuspan 4 gm IV over 5-10 min 1–2 gm/hour IV infusion
Sibai 6 gm Iv over 20 min 2 gm/hour IV infusion
Regimens for the administration of magnesium sulfate for seizure prophylaxis in women in labor with preeclampsia
a. 10 g (5 g IM deep in each buttock)
b. 5 g IM deep q4h,alternating sides
a. 6-g bolus over 15 min
b. 1–3 g/h by continuous infusion pump
c. May be mixed in 100 mL crystalloid; if given by intravenous push, make up as 20% solution; push at maximum rate of 1g/min. 40-g MgSO4.7H2O in 1000 mL Ringers lactate; run at 25–75 mL/h (1–3 g/h).