Sodium haemostasis and osmolality

Question 1

What is normal serum osmolality?

Answer 1

282-295mOsm/L

Question 2

Difference between CSW and SIADH

Answer 2

CSW volume depletion with Na loss, SIADH - euvolaemic or hypervolaemic
Note both can have high urinary Na

Question 3

SIADH seen in particular with which disease?

Answer 3

Small cell lung Ca

Question 4

What percentage of head injuries affected by SIADH?

Answer 4

4.6%

Question 5

Drugs used in neurosurgery that cause SIADH

Answer 5

Carbemazepine/oxycarbemazepine
NSAIDS
antipsychotics
DDAVP

Question 6

What is the risk of over rapid correction of Na?

Answer 6

Osmotic demyelination (including cerebral pontine myelinolysis)

Question 7

2 causes of acute hyponatraemia outside of hospital

Answer 7

ecstasy

marathoners

Question 8

What type of hyponatraemia does mannitol cause?

Answer 8

Hypertonic hyponatraemia (pseudohyponatraemia)

Question 9

Addisons gives what picture of hyponatraemia?

Answer 9

same as CSW - Low Na, Low Serum osmo, volume depleted, high urinary Na

Question 10

What is Schwartz-Bartter syndrome?

Answer 10

SIADH first described with small cell lung Ca

Question 11

Essential features of diagnosing SIADH?

Answer 11

Low Na, paired serum (low) and urinary (high) osmos
clinically euvolaemic
Normal thyroid function and no diuretic use

Question 12

Definitive test for SIADH?

Answer 12

Water load test - consume 20ml/kg water up to 1.5L, 65% should be excreted within 4 hours

Note this should not be done in patients with severe or symptomatic hyponatraemia!

Question 13

What is Conivaptan?

Answer 13

Type V1A and V2 vasopressin receptor blocker used in severe hyponatraemia

Question 14

What is the treatment of CSW?

Answer 14

Postive salt balance

fluid replacement

Question 15

What medications can be used to help treat CSW?

Answer 15

Fludrocortisone

Urea can be used in CSW and SIADH

Question 16

What is the definitive test for DI?

Answer 16

Water deprivation test