Hyponatraemia

Question 1

Concentration of serum sodium is determined by

Answer 1

The total body water

Question 2

Which electrolyte is a main determinants of effective osmolality within the extracellular fluid

Answer 2

Sodium

Question 3

Define osmolality

Answer 3

The concentration of a solute dissolved in a solution

Question 4

What is the formula to calculate osmolality

Answer 4

2Na + Urea + Glucose

Question 5

What is the key hormone involved in osmoregulation

Answer 5

Antidiuretic hormone (ADH)

Question 6

What is the other name for Antidiuretic hormone (ADH)

Answer 6

Vasopressin

Question 7

How does ADH reduce the plasma osmolality

Answer 7

It stimulates the insertion of aquaporin-2 channels onto the luminal membrane of the distal convoluted tubule and collecting duct of the kidney to increase water reabsorption (independent of sodium)

Question 8

The causes of hyponatraemia can be split into 3 categories: Hypovolaemic hyponatraemia, Euvolaemic hyponatraemia, hypervolaemic hyponataemia.

Define Hypovolaemic hyponatraemia

Answer 8

Reduction in extracellular fluid state with a greater loss of sodium relative to total body water

Question 9

The causes of hyponatraemia can be split into 3 categories: Hypovolaemic hyponatraemia, Euvolaemic hyponatraemia, hypervolaemic hyponataemia.

Define Euvolaemic hyponatraemia

Answer 9

Hyponatraemia with normal extracellular fluid status

Question 10

The causes of hyponatraemia can be split into 3 categories: Hypovolaemic hyponatraemia, Euvolaemic hyponatraemia, hypervolaemic hyponataemia.

Define Hypervolaemic hyponataemia

Answer 10

Increase in extracellular fluid status with an increase in total body water relative to sodium

Question 11

Give examples of causes that causes hyponatraemia secondary to hypovolaemic hyponatraemia

Answer 11

Reduction in extracellular fluid state with a greater loss of sodium relative to total body water

GI losses e.g. severe diarrhoea, vomiting

Skin losses e.g., sweating, burns

Addison’s disease

Third space losses in sepsis

Question 12

Give examples of causes that causes hyponatraemia secondary to euvolaemic hyponatraemia

Answer 12

Hyponatraemia with normal extracellular fluid status

Syndrome of inappropriate ADH release (SIADH) – most common cause

Hypothyroidism

Question 13

What is the most common cause of hyponatraemia

Answer 13

SIADH

Question 14

Give examples of causes that causes hyponatraemia secondary to hypervolaemic hyponatraemia

Answer 14

increase in extracellular fluid status with an increase in total body water relative to sodium

• Renal failure
• Heart failure
• Liver failure
• Nephrotic syndrome

Question 15

What kind of symptoms do the majority of patients with hyponatraemia have

Answer 15

Majority are asymptomatic

Question 16

The majority of hyponatraemia cases are asymptomatic.

If there are symptoms, give examples of them

Answer 16

• Headache
• Confusion
• Nausea and vomiting
• Lethargy
• Irritability
• Seizures
• Loss of consciousness
• Coma

Question 17

Neurological symptoms are suggestive of what level of hyponatraemia

Answer 17

Severe hyponatraemia

Question 18

Name some signs of hypovolaemia

Answer 18

Dry mucous membranes

Capillary refill time > 2 seconds

Dizziness

Thirst

Postural drop in systolic blood pressure

Tachycardia

Question 19

Name some signs of hypervolaemia

Answer 19

Raised JVP

Bibasal crackles

Gallop rhythm

Peripheral oedema

Hypertensive

Question 20

How is hyponatraemia diagnosed

Answer 20

Diagnosed based on the finding, often incidental, of a low serum sodium concentration on blood testing

Urinary sodium and osmolarity levels aid making a diagnosis

Question 21

How is hyponatraemia managed

Answer 21

Depends on the cause – majority is treat the underlying pathology

Question 22

In general, how is hypovolaemic hyponatraemia managed

Answer 22

IV normal saline

Question 23

In general, how is hypervolaemic hyponatraemia managed

Answer 23

Fluid restrict + diuretics

Question 24

What are two potential complications of hyponatraemia

Answer 24

Osmotic demyelination syndrome – if corrected too fast

Cerebral oedema