Clincial Lect Salt

Question 1

What’s the main cause for serum osmolarity being low (hyponatraemia)?

Answer 1

Too much H20 in blood (almost always the cause)

Question 2

What’s the much rarer reason for hyponatraemia and what are some causes?

Answer 2

True deficits in Na

Causes:

• severe diarrhoea
• diuretics/ renal failure
• peritonitis
• severe burns
• cystic fibrosis

Question 3

What is SIADH and what are some Symptoms and causes for it?

Answer 3

Symptom of inappropriate ADH secretion -> hyponatraemia

Symptoms:

• normal/ mild
• acute neurological
• nausea
• coma
• seizures
• agitation

Causes: 
-primary Brain injury 
(Meningitis/ subarachnoid haemorrhage)
- infective (pneumonia)
-hypothyroidism 
- kidneys 
-malignancy (small cell lung cancer) 
- drugs (epileptic meds carbamazepine + valproate, PPIs, ACE inhibitors or some SSRIS) 
- heart failure

Question 4

How serious is hyponatraemia?

Answer 4

Very serious

20% mortality if due to H20 homeostasis

Question 5

How can you tell if hyponatraemia has a pathological cause?

Answer 5

Urine osmolarity will be much higher (inappropriate reabsorption of H2O)

Question 6

What are the stages done to test the reason for hyponatraemia?

Answer 6

1. Calculate blood osmolarity - if true loss or not (if another solute balancing blood e.g. high serum glucose then normal)
   If hypertonic…
2. Fluid assessment ECF - jugular venous pressure, skin turgor
   (If not true Na loss)
   If fluid-overloaded…
3. Urine Na - if high acute/ chronic renal failure, SIADH (if low polydsipsia, if oedematous and low heart failure)

Slide 30

Question 7

How do you treat hyponatraemia?

Answer 7

• fluid restriction
• hypertonic salt H2P IV
• diuretics (often not used)

Question 8

Why are diuretics often not used to treat hyponatraemia?

Answer 8

Cerebral compensates for low Na over chronic period so quick correction -> neurones exposed to hypertonic solution and H2O leaves neurones -> irreversible demyelination -> paralysis
‘Central pontine myelinolysis’