Magnesium Sulphate Flashcards
How can MgSO4 be administered?
IV, IM, Oral
What incidences would we use Mag Sulph?
- Severe Pre-eclampsia
- Eclampsia
- Fetal Neuroprotection
What was the Magpie Trial’s main finiding?
MgSO4 administered to women with pre-eclampsia more than halves the risk of eclampsia. Risk of seizure was 58% lower.
What 3 things may MgSO4 do? (Not well understood)
- Prevent vasospasm by acting as a Calcium antagonist
- Acts as vasodilator to decrease peripheral vascular resistance or relive vasoconstriction
- Acts through a central anticonvulsant action
What is meant by ‘Calcium antagonist?’
Competitively blocks intracellular calcium channels, decreasing calcium availability and thus inhibiting smooth muscle contractility.
What is the dosing regime (Pre-eclampsia)?
Loading dose: 4g MgSO4 IV bolus over 5-10 minutes
Maintenance therapy: 1g MgSO4 per hour IV by pump
What is the dosing regime (Eclampsia)?
Loading dose: 4g MgSO4 IV bolus over 5-15 minutes
Maintenance therapy: 1g MgSO4 per hour IV by pump for 24 hours
What should be done with the infusion if the woman has had an eclamptic fit?
Continued for 24 hours after the last fit
What should be done with the infusion if the woman has recurrent fits?
Further doses of 2-4mg given via IV over 5-15 minutes.
Consider other causes of seizure.
How is significant toxicity treated?
1g Calcium Chloride or Calcium Gluconate (10% w/v solution) by slow IV injection over 3 minutes
What is the single biggest cause of neonatal mortality and morbidity in the UK?
Preterm birth (<37 weeks)
What is prevented using MgSO4 in preterm infants?
Cerebral palsy and motor deficits
At what gestation should MgSO4 be offered for babies who are in established preterm labour or having a planned preterm birth within 24 hours?
24+0 - 29+6
What gestation babies should be CONSIDERED for MgSO4 who are in established preterm labour or having a planned preterm birth within 24 hours?
30+0 - 33+6
When should MgSO4 be administered before delivery?
4 hours prior
What is the closest it can be given where benefits have been seen?
15 minutes prior to delivery
What is MgSO4 mode of action for fetal neuroprotection?
Rapid crossing of the placenta and entry into fetal brain within minutes.
Blocks glutamate receptors on the surface of the brain preventing uptake of calcium ions into the brain thus preventing cell death.
What benefits are reported to happen with administration of MgSO4 in relation to neuroprotection?
- Improvement of placental blood flow by increasing nitrous oxide synthases (NOS)
- Increase vascular response to dilators (vasodilation)
- Reduce inflammation and oxidative stress
- Reduce neuronal excitability
What is the dosing regime of MgSO4 for fetal neuroprotection?
Give 4g IV bolus of MgSO4 over 15 minutes, followed by IV infusion of 1g per hour until birth or for 24 hours (whichever is sooner)
What monitoring should be done on MgSO4?
Continuous:
- O2 sats (>95%)
- Void (>100ml/4 hours)
Intermittent:
- RR (>12/min)
- BP and Pulse
When should the observations be monitored?
- prior to loading dose
- 10 mins after loading dose
- at the end of loading dose
- hourly during infusion
When should the infusion be stopped?
- RR decrease more than 4 breaths per min below baseline
- RR <12
- DS BP decreases more than 15mmHg below baseline level
What is an indication for receiving half the loading and maintenance dose?
- Women with renal impairment (serum creatinine >90 umol/L)
Check Mg levels 4 hours after and recheck depending on initial result. Therapeutic range is 2-4 mmol/L
What can babies with hypermagnesemia experience?
- Hypotonia
- Apnoea
What needs to happen if a mother has been given repeated courses of MgSO4? (5-7 days cumulatively)
A serum bone profile needs to be taken from the baby - neonatal team to be informed at this level of exposure
What level of Mg is excreted in urine?
97% - oliguria can lead to toxic levels
In the event of severe toxicity leading to cardiorespiratory arrest, what is the procedure?
- stop infusion
- dial 2222 and declare maternal cardiac arrest
- Initiate CPR
- Administer 10ml Calcium Gluconate IV
- Intubate immediately and manage with assisted ventilation
In what sequence are vital functions lost in the event of Mg overdose?
- Loss of tendon reflexes (5mmol/L)
- Sleepy/drowsy/confusion/altered mental state (5mmol/L)
- Respiratory depression
- Paralysis (6-7.5mmol/L)
- Cardiac arrest (>12mmol/L)
What are common maternal side effects of MgSO4?
- Flushing, sweating
- Vomiting
- Headaches
- Palpitations
What are serious adverse effects of MgSO4?
- Respiratory depression
- Respiratory or cardiac arrest
- Death
