Endocrinology: Acute Hyponatraemia

Question 1

Outline the pathophysiology of hyponatraemia, including Post-op pathophysiology

Answer 1

Mild 130-135, moderate 125-130, severe <125mmol/l

Na is a large contributor to plasma osmolarity

Low plasma osmolarity = water moves intracellularly = cerebral oedema, RICP, reduced cerebral blood flow, tissue oedema (impaired tissue healing)

Post-op: - Stress response = increased cortisol and ADH = Free water reabsorption in excess of Na.

Question 2

Outline the aetiology of hyponatraemia.

Answer 2

Question 3

Outline the signs and symptoms of hyponatraemia.

Answer 3

Asymptomatic

Malaise

Headache

Confusion

Reduced consciousness

Seizures

Question 4

How would you investigate hyponatraemia?

Answer 4

Urine osmolality = <100 ADH normal, >100 impaired diluting SIADH

Urine [Na]

Serum osmolality = <280

Serum Na

Question 5

How would you manage hyponatraemia?

Answer 5

Close fluid monitoring

Catheter

IV fluids

Monitor U+E regularly

Question 6

What are the potential complications of rapid correction of hyponatraemia?

Answer 6

Rapid Na correction = central pontine myelinolysis (quadrantinopia, respiratory paralysis, mental status changes, fatal in 3-5 weeks) – large change in extracellular osmolarity causes damage to the myelin sheaths

DO NOT CORRECT MORE THAN 12mmol/L PER DAY!

Question 7

Why can a pt with hyponatraemia have seizures?

Answer 7

Severe hyponatraemia <125 = low plasma osmolarity, water moves intracellularly, cerebral oedema, RICP, reduced cerebral blood flow