Hyponatraemia

Question 1

What is the definition of hyponatraemia?

Answer 1

Serum Na+ less than 135 meq/L

Question 2

What is a common reason of hyponatraemia?

Answer 2

Increased intake and retention of water

Question 3

How can the cause of hyponatraemia be determined?

Answer 3

Based on the level of:

• ADH
• Serum osmolality

Question 4

What could be the causes of hyponatraemia with a high ADH?

Answer 4

Hypovolaemia - D&V, thiazide diuretics

Hypervolaemia - Heart failure, Liver cirrhosis

Other - SIADH, Exercise-induced, MDMA, hypothyroid, pregnancy

Question 5

How can heart and liver failure cause a hypervolaemic hyponatraemia?

Answer 5

Since reduced perfusion pressure causes increased ADH causing increased water reabsorption

Question 6

What are some of the causes of SIADH?

Answer 6

CVA
Infections
Neoplasia - small cell lung Ca, pancreatic
Drugs - antiepileptics, antimitotics, ABX, Amiodorone
Surgery
Pulmonary - pneumonia, TB, sarcoidosis
HIV
Endocrine - hypoadrenal, hypothyroid

Question 7

What could be the causes of hyponatraemia with a low ADH?

Answer 7

Renal failure - impairment in free water excretion

Polydipsia

Question 8

What could be the causes of hyponatraemia with if a normal/high serum osmolality?

Answer 8

Renal failure
Marked hyperglycaemia / DKA
Mannitol therapy
Noncondutive irrigation solutions
Pseudohyponatraemia

Question 9

Common symptoms of hyponatraemia?

Answer 9

Nausea and Confusion
Headache and Lethargy
Convulsions, coma

Question 10

What are the signs of hyponatraemia?

Answer 10

Fluid loss => skin turgor, postural hypotension

Oedema, ascites, additional sounds, liver disease

SIADH - pulmonary, CNS, drugs etc.

Adrenal insufficiency / hypothyroidism

Question 11

What is the normal serum osmolality range?

Answer 11

275-290 mosmol/kg

• normally low in hyponatraemic patients

Question 12

Describe the urine osmolality in hyponatraemic patients?

Answer 12

Usually high in most patients ~ 300 mosmol/kg

Question 13

Describe the urinary Na+ concetration in hyponatraemic patients

Answer 13

40 mmol/L) in SIADH

Question 14

Describe the investigation results of a hyponatraemia due to SIADH

Answer 14

Low serum osmolality
Low serum Na+
Low blood urea
High urine osmolality
High urinary Na+
Normal acid base balance
Normal adrenal and thyroid function

Question 15

How should hyponatraemia be treated?

Answer 15

Treat cause

Fluid restriction if: heart failure, nephrotic syndrome, SIADH, primary polydipsia, CKD

Salt replacement - oral tablets, isotonic saline in volume deplete patients

Loop diuretics may be useful in SIADH

Vaspopressin (ADH)-receptor antagonist - in refractory heart failure, liver cirrhosis, oedema, SIADH

Question 16

What is osmotic demyelination syndrome?

Answer 16

A complication of rapid correction of severe hyponatraemia

Sx usually develop 2-6 days after correction

• dysarthria
• dysphagia
• paraparesis/quadraparesis
• behavioural disturbance
• lethargy, confusion, disorientation
• obtundation
• coma
• seizures
• locked in syndrome

Question 17

How does treatment change based on severity of hyponatraemia?

Answer 17

Mild => fluid restriction
Moderate => fluid restriction + salt replacement
Severe => hypertonic saline +/- vasopressin blocker