MgSo4 Preparation

Slow Bolus

(4gm in 10-15min)

• 1 ampule= 5ml MgSo4 = 2.5gm so
• 1 1/2 ampule= 8ml MgSo4 = 4gm
• [use 20cc syringe, take 8ml MgSo4 + 12ml Normal Saline]

* use 3 way branula, give infusion while we also run Normal Saline for 15 min

Maintenance

10 ampule = 50ml MgSo4 = 25gm

• [use 50cc syringe]
• infusion 2cc/hr/24hr = 1g/hr

*1 ampule contain 2.47gm Mgso4

MgSo4 MOA

The mechanism of action of Magnesium sulfate in eclampsia is not clear. The postulated mechanisms are:

a. Central action: Voltage dependent blockade of NMDA (N-methyl D-aspartate) subtype of glutamate (excitatory) channel receptors

b. Peripheral action: At Neuromuscular Junction (NMJ), it causes –

1. Blockage of calcium entering the cell and blocking calcium at intracellular sites/membranes
2. Reduction of presynaptic acetylcholine (ACh) release at the endplate
3. Reduction of motor endplate sensitivity to acetylcholine (ACh)

Role in Severe pre-eclampsia and Eclampsia:

Magnesium sulfate is an anticonvulsant rather than an anti-hypertensive. It prevents seizures in pre-eclampsia and doesn’t treat hypertension. In eclampsia, it is given as soon as the convulsion has ended.

It causes vasodilation, increases cerebral, uterine and renal blood flow. It decreased cerebral edema.

Monitoring Hourly for Magnesium Sulfate toxicity:

Suspend or postpone use of Magnesium sulfate, if any of the following is present:

1. Respiratory rate < 16/min (Respiratory depression)
2. Absent patellar reflex (Muscle paresis)
3. Urine output < 30 ml/hour in preceding 4 hours (Impaired renal function)

Magnesium sulfate is preferred over Diazepam and Phenytoin because:

1. Relatively less depression effect to mother or fetus
2. Reduced risk of convulsions