Hypomagnesaemia

Question 1

Normal Mg level

Answer 1

0.7 to 1 mmol/L

Question 2

Cause of hypomagnesaemia

Answer 2

• Diuretics:
  
  • Loop diuretics: Furosemide/Frusemide
  • Thiazide
• TPN (Total parenteral nutrition)
• NG feeding
• Diarrhoea
• Alcohol
• Hypokalaemia
• IBD (Inflammatory bowel disease)
• Gitleman’s syndrome
• Bartter’s syndrome
• Cisplatin

Question 3

Hypomagnesaemia: Features

Answer 3

• Neurological:
  
  • Paraesthesia
  • Tetany
  • Seizures
• Cardiac:
  
  • Arrhythmias
  • ECG abnormal
  • Exacerbates digoxin toxicity
• Hormonal:
  
  • Lowers PTH secretion → hypocalcaemia
    
    • ​Mainly low Mg → low Ca; First correct “low Mg” to reverse “low Ca”

Question 4

Hypomagnesaemia: ECG changes

Answer 4

• PR >>> Prolonged PR
• QT >>> Long QT
• ST >>> ST depression
• T >>> Small/absent T (maybe inversion)

​Above findings are also common to hypokalaemia (but hypokalaemia has U wave, which is absent in hypomagnesaemia)

Question 5

Hypomagnesaemia: Treatment

Answer 5

Normal Mg level: 0.7 to 1 mmol/L

• <0.4 mmol/L → TOC: IV MgSO₄ 40mmol over 24hours
• 0.4 to 0.7 mmol/L → TOC: Oral MgSO₄ 10-20mmol per day

​S/E: Diarrhoea

Question 6

MgSO₄: Indications

Answer 6

• Polymorphic VT (Torsades de pointes)
• Severe asthma
• Prev. and treatment of eclampsia (also used in severe pre-eclampsia)
• Hypomagnesaemia

Question 7

MgSO₄: side effect

Answer 7

Diarrhoea

Question 8

Chronic hypermagnesaemia: Features

Answer 8

• Nausea
• Dirrhoea
• Confusion
• Coma
• Hypertension
• Reduced deep tendon reflex