Magnesium Sulphate

Question 1

How can MgSO4 be administered?

Answer 1

IV, IM, Oral

Question 2

What incidences would we use Mag Sulph?

Answer 2

• Severe Pre-eclampsia
• Eclampsia
• Fetal Neuroprotection

Question 3

What was the Magpie Trial’s main finiding?

Answer 3

MgSO4 administered to women with pre-eclampsia more than halves the risk of eclampsia. Risk of seizure was 58% lower.

Question 4

What 3 things may MgSO4 do? (Not well understood)

Answer 4

• 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

Question 5

What is meant by ‘Calcium antagonist?’

Answer 5

Competitively blocks intracellular calcium channels, decreasing calcium availability and thus inhibiting smooth muscle contractility.

Question 6

What is the dosing regime (Pre-eclampsia)?

Answer 6

Loading dose: 4g MgSO4 IV bolus over 5-10 minutes

Maintenance therapy: 1g MgSO4 per hour IV by pump

Question 7

What is the dosing regime (Eclampsia)?

Answer 7

Loading dose: 4g MgSO4 IV bolus over 5-15 minutes

Maintenance therapy: 1g MgSO4 per hour IV by pump for 24 hours

Question 8

What should be done with the infusion if the woman has had an eclamptic fit?

Answer 8

Continued for 24 hours after the last fit

Question 9

What should be done with the infusion if the woman has recurrent fits?

Answer 9

Further doses of 2-4mg given via IV over 5-15 minutes.

Consider other causes of seizure.

Question 10

How is significant toxicity treated?

Answer 10

1g Calcium Chloride or Calcium Gluconate (10% w/v solution) by slow IV injection over 3 minutes

Question 11

What is the single biggest cause of neonatal mortality and morbidity in the UK?

Answer 11

Preterm birth (<37 weeks)

Question 12

What is prevented using MgSO4 in preterm infants?

Answer 12

Cerebral palsy and motor deficits

Question 13

At what gestation should MgSO4 be offered for babies who are in established preterm labour or having a planned preterm birth within 24 hours?

Answer 13

24+0 - 29+6

Question 14

What gestation babies should be CONSIDERED for MgSO4 who are in established preterm labour or having a planned preterm birth within 24 hours?

Answer 14

30+0 - 33+6

Question 15

When should MgSO4 be administered before delivery?

Answer 15

4 hours prior

Question 16

What is the closest it can be given where benefits have been seen?

Answer 16

15 minutes prior to delivery

Question 17

What is MgSO4 mode of action for fetal neuroprotection?

Answer 17

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.

Question 18

What benefits are reported to happen with administration of MgSO4 in relation to neuroprotection?

Answer 18

• 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

Question 19

What is the dosing regime of MgSO4 for fetal neuroprotection?

Answer 19

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)

Question 20

What monitoring should be done on MgSO4?

Answer 20

Continuous:

• O2 sats (>95%)
• Void (>100ml/4 hours)

Intermittent:

• RR (>12/min)
• BP and Pulse

Question 21

When should the observations be monitored?

Answer 21

• prior to loading dose
• 10 mins after loading dose
• at the end of loading dose
• hourly during infusion

Question 22

When should the infusion be stopped?

Answer 22

• RR decrease more than 4 breaths per min below baseline
• RR <12
• DS BP decreases more than 15mmHg below baseline level

Question 23

What is an indication for receiving half the loading and maintenance dose?

Answer 23

• 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

Question 24

What can babies with hypermagnesemia experience?

Answer 24

• Hypotonia

- Apnoea

Question 25

What needs to happen if a mother has been given repeated courses of MgSO4? (5-7 days cumulatively)

Answer 25

A serum bone profile needs to be taken from the baby - neonatal team to be informed at this level of exposure

Question 26

What level of Mg is excreted in urine?

Answer 26

97% - oliguria can lead to toxic levels

Question 27

In the event of severe toxicity leading to cardiorespiratory arrest, what is the procedure?

Answer 27

• stop infusion
• dial 2222 and declare maternal cardiac arrest
• Initiate CPR
• Administer 10ml Calcium Gluconate IV
• Intubate immediately and manage with assisted ventilation

Question 28

In what sequence are vital functions lost in the event of Mg overdose?

Answer 28

1. Loss of tendon reflexes (5mmol/L)
2. Sleepy/drowsy/confusion/altered mental state (5mmol/L)
3. Respiratory depression
4. Paralysis (6-7.5mmol/L)
5. Cardiac arrest (>12mmol/L)

Question 29

What are common maternal side effects of MgSO4?

Answer 29

• Flushing, sweating
• Vomiting
• Headaches
• Palpitations

Question 30

What are serious adverse effects of MgSO4?

Answer 30

• Respiratory depression
• Respiratory or cardiac arrest
• Death