Sodium

Question 1

What is pseudohyponatremia?

Answer 1

In some patients with very high plasma protein (myeloma) or high lipid levels there is a discrepancy between the low measured plasma sodium and the normal plasma osmolarity.

Normal osmolality and low Na+
Normally, a fall in sodium should cause a decrease in plasma osmolarity

Question 2

What are the symptoms of hyponatraemia?

Answer 2

o Headache
o Nausea
o Dizziness
o Severe = coma

Question 3

What are the signs of hypovolaemia?

Answer 3

• Cool peripheries/prolonged CRT
• Tachycardia/weak, thready pulse
• Postural hypotension
• Confusion
• Dry mucous membranes
• Reduced skin turgor

Question 4

What are the signs of hypervolaemia?

Answer 4

• Tachycardia/bounding pulse
• Raised JVP
• Pulmonary oedema or pleural effusions
• Ascites
• Peripheral oedema

Question 5

After hydration status what can you measure to aid with diagnosis?

Answer 5

Urinary sodium and osmolality

Question 6

What is osmolality?

Answer 6

The number of particles of solute per litre of solution

Question 7

How is serum osmolality calculated?

Answer 7

2(Na + K) + urea + glucose

Question 8

What is hypertonic hyponatraemia, and what does it indicate?

Answer 8

• Serum osmolality > 295 mmol/kg

Hyperglycaemia
Hypertonic fluids

Question 9

What is hypotonic hyponatraemia, and what does it indicate?

Answer 9

• Serum osmolality < 275 mmol/kg

Thiazide diuretics
Primary adrenal insufficiency
GI losses
Third-space losses

Question 10

What is pseudohyponatraemia, and what does it indicate?

Answer 10

• Serum osmolality 275-295 mmol/kg

Falsely low Na+ due to hyperproteinaemia or hypertriglyceridemia

Question 11

If urine osmolality is ≤100 mOsm/kg, what does it indicate?

Answer 11

Lots of water in urine, as ADH is not acting

• Primary water overload due to polydipsia
• Low solute intake
• High beer intake

Question 12

If urine osmolality is >100 mOsm/kg, what does it indicate?

Answer 12

ADH is acting

Question 13

How is urinary sodium measured?

Answer 13

Concentration of Na+ in 1 litre of urine

Question 14

What does it indicate if a patient is:
• Hypovolaemic
• Urine osmolarity >100 mOsm/kg
• Urine Na+ ≤30 mmol/L

Answer 14

• Vomiting
• Diarrhoea
• Burns
• Third space losses
• Sweating
• Recent diuretic use

Question 15

What does it indicate if a patient is:
• Hypervolaemic
• Urine osmolarity >100 mOsm/kg
• Urine Na+ ≤30 mmol/L

Answer 15

• HF
• Liver cirrhosis
• Renal failure

Question 16

What does it indicate if a patient is:
• Hypovolaemic
• Urine osmolarity >100 mOsm/kg
• Urine Na+ >30 mmol/L

Answer 16

• Vomiting
• Addison’s disease,
• Renal-salt wasting
• Cerebral-salt wasting
• Non-prescribed diuretics

Question 17

What does it indicate if a patient is:
• Euvolaemic
• Urine osmolarity >100 mOsm/kg
• Urine Na+ >30 mmol/L

Answer 17

• SIADH
• Secondary adrenal insufficiency,
• Hypothyroid
• Non-prescribed diuretics

Question 18

In hypernatraemia with euvolaemia, what indicates extrarenal loss?

Answer 18

Extrarenal loss: urine:plasma osmolarity >1
• Inadequate water intake (CVA, confusion)
• Skin loss and low intake (fever, burns)

Question 19

In hypernatraemia with euvolaemia, what indicates renal loss?

Answer 19

Renal loss: urine:plasma <1
• Cranial diabetes insipidus
• Nephrogenic diabetes insipidus

Question 20

What causes hypernatraemia with hypervolaemia?

Answer 20

• Iatrogenic – IV sodium bicarbonate infusion
• Salt ingestion – accidental, sea water drowning
• Mineralocorticoid excess – usually only mild hypernatremia

Question 21

In hypernatraemia with hypovolaemia, what indicates extrarenal loss?

Answer 21

Extrarenal loss: urine:plasma osmolarity >1
• GI (vomiting, diarrhoea, fistula)
• Excessive sweating

Question 22

In hypernatraemia with hypovolaemia, what indicates extrarenal loss?

Answer 22

Renal loss: urine:plasma osmolarity approx. 1
• Hyperosmolar diabetic coma
• Renal failure