Hypernatraemia

Question 1

What is Central Pontine Myelinolysis?

Answer 1

Devastating / fatal condition associated with rapid correction of hyponatraemia
-related to water fluxes into & out of brain
-commoner in alcoholism & malnutrition (and young women)
=mostly iatrogenic causes

Question 2

What is the recommended rate of correction for Central Pontine Myelinolysis?

Answer 2

• 4-10 mmol/l/day if asymptomatic
• 8-12 mmol/l/day if symptomatic
• with careful monitoring / observation

Question 3

Describe hypernatraemia

Answer 3

• Hypovolaemia is almost always the case (concentration)
• The list of potential aetiologies is very similar to that for hypovolaemic hyponatraemia:
• The difference is the sodium : water balance

Question 4

Why does hypernatremia occur in a case with colostomy and gastroenteritis?

Answer 4

-Colonic secretions are water&raquo_space; salt
-Salt is already absorbed in small bowel
-Water loss causes hypernatraemia
-Osmotic and hydrostatic forces favour shifts from cells to ECF (extra-cellular)
( but not enough to concentrate sodium back up )

Question 5

What are the causes of hypernatraemia?

Answer 5

-Water loss:
=fever
=hyperventilation
=diabetes insipidus
-Reduced water intake:
=iatrogenic
=psychosocial - elderly, infants, apathetic etc.
=stroke, coma, confusion etc.
-High sodium intake:
=iatrogenic
=concentrated feeds
=emetics
=uncommon

Question 6

What is Diabetes insipidus?

Answer 6

-ADH is insufficient / inactive
=diuresis continues unabated
=free water loss occurs
=sodium is concentrated
=hypernatraemia occurs
=no / failed feedback mechanism

Question 7

What are the causes of diabetes insipidus?

Answer 7

-Cranial/ central: non/ reduced synthesis
=pituitary tumour
=head injury
=meningitis
=genetic
=idiopathic
-Nephrogenic: reduced tubular response
=inherited
=drugs (lithium- BPD)

Question 8

What is the treatment for diabetes insipidus?

Answer 8

-Can be very difficult
-Hydration tends to simply cause polyuria
-Synthetic ADH ( DDAVP ) exists
=works in central / cranial DI
=supranormal doses might work in nephrogenic DI
=NSAIDs might help

Question 9

What needs to be investigated in hypernatraemia?

Answer 9

-Thorough history:
=recent events (hospital/ meningitis...)
=new prescriptions
=what’s in the drip ?
-Examination:
=assessment of volume state ( can be difficult )
=cardiac / respiratory / neurological disease
=examine the drug Kardex and IV chart

Question 10

What tests are used to investigate hypernatraemia?

Answer 10

=Other electrolytes
=Infection screen
=Chest X-ray
=Serum cortisol / =Synacthen test
=CT brain

=Urinary sodium concentration
=Serum and urine osmolalities