Magnesium Sulphate & Management of Eclampsia

• occurrence of new-onset, generalized, tonic-clonic seizures or coma in a woman with preeclampsia.
• convulsive manifestation of preeclampsia and one of several clinical manifestations at the severe end of the preeclampsia spectrum

Management
1. Maternal oxygenation and protection from trauma

• The patient is placed in a lateral position, if possible. 
• Supplemental oxygen (8 to 10 L/min) is administered via a nonrebreather face mask to treat hypoxemia from hypoventilation during the seizure
• Raised, padded bedrails provide protection from trauma

2. Treatment of hypertension 

• administered to prevent stroke, which accounts for 15 to 20 percent of deaths from eclampsia
• common threshold for initiating antihypertensive therapy is sustained diastolic pressures greater than 105 to 110 mmHg or systolic blood pressures ≥160 mmHg
• treatment of hypertension, drug choice and dose, and target blood pressure are the same as in preeclampsia

3. Prevention of recurrent seizures

• anticonvulsive drug of choice is magnesium sulfate
• directed at prevention of recurrent seizures rather than control of the initial seizure 
• Magnesium sulfate is the drug of choice based on randomized trials demonstrating that it reduces the rate of recurrent seizures by one-half to two-thirds
• magnesium sulfate was safer and more effective than phenytoin, diazepam, or lytic cocktail (ie,chlorpromazine, promethazine and pethidine) for prevention of recurrent seizures in eclampsia 

Administration of Magnesium Sulphate
Loading dose

• Loading doses of 4 to 6 g intravenously over 15 to 20 minutes are commonly used

Maintainence Dose

• Maintenance doses of 1 to 3g/hour are commonly used
• renal insufficiency - maintenance dosing should be lower and dosed in consultation and magnesium levels should be monitored
• if the serum creatinine is >1.5 mg/dL(133 micromol/L) or if the urine output is <20 mL per hour, hold the maintenance infusion  and recheck the magnesium level in six hours. 
• If the serum creatinine is 1.0 to 1.5 mg/dL (88 to 133 micromol/L)and the urine output is adequate, the maintenance infusion is reduced by half to 1 g /hour and a magnesium level is rechecked in six hours
• A clear threshold magnesium concentration for  prevention of seizures has not been established, [range of 4.8 to 8.4 mg/dL(424 to 743 micromol/L)]
• Calcium gluconate (1 g IV) may be administered to counteract magnesium toxicity

 South Australian Perinatal Practice Guidelines

Management of Persistent Seizures

• Recurrent seizures in patients on maintenance magnesium sulfate therapy can be treated with an additional bolus of 2 g magnesium sulfate over 5 to 10 minutes
• frequent monitoring for signs of magnesium toxicity (eg, loss of patellar reflex, respirations <12 per minute)
• If two such boluses do not control seizures, then other drugs should be given.Diazepam or lorazepam is a common choice

Diazepam 

• 5 to 10 mg intravenously every 5 to 10 minutes at a rate ≤5 mg/minute and maximum dose 30 mg. Diazepam will control seizures within 5 minutes in over 80 percent of patients 
• Some experts recommend avoiding benzodiazepines for management of eclamptic seizures because of potentially profound depressant effects on the fetus and mother. 
• This effect becomes clinically significant when the total maternal dose ofdiazepam exceeds 30 mg

Lorazepam 

• 4 mg intravenously at maximum rate 2 mg/minute. Lorazepam is as effective as diazepam for terminating seizures
• clinical advantage of lorazepam is that the effective duration of protection from additional seizures is as long as four to six hours

Midazolam 

• 1 to 2 mg bolus given intravenously at a rate of 2mg/min. Additional boluses can be given every five minutes until seizures stop (up to a maximum of 2 mg/kg). 
• advantage of midazolam is its short duration of action, which may minimize maternal postictal confusion and fetal effects

PostPartum Care

• Duration of magnesium sulfate therapy — Seizures due to eclampsia always resolve postpartum, generally within a few hours to days. 
• Diuresis (greater than 4 L/day) is believed to be the most accurate clinical indicator of resolution of preeclampsia/eclampsia but is not a guarantee against the development of seizures
• optimal duration of magnesium sulfate therapy has not been determined. 
• When begun before delivery, continue magnesium sulfate for 24 to 48 hours postpartum, when the risk of recurrent seizures is low. 
• When begun for postpartum eclampsia, maintain therapy for 24 to 48 hours. 
• therapy is continued in women whose disease has not started to improve and discontinued in women who are clearly improving clinically (eg, diuresis of ≥100mL/hour for two consecutive hours and the absence of symptoms). 

References:

1. www.uptodate.com
2. http://www.kemh.health.wa.gov.au/development/manuals/O&G_guidelines/sectionb/2/b2.2.3.6
3. https://www.sahealth.sa.gov.au/wps/wcm/connect/dbb027004ee4f22091c79dd150ce4f37/Magnesium-sulphate-infusion-regimen