Hyponatraemia Flashcards
Concentration of serum sodium is determined by
The total body water
Which electrolyte is a main determinants of effective osmolality within the extracellular fluid
Sodium
Define osmolality
The concentration of a solute dissolved in a solution
What is the formula to calculate osmolality
2Na + Urea + Glucose
What is the key hormone involved in osmoregulation
Antidiuretic hormone (ADH)
What is the other name for Antidiuretic hormone (ADH)
Vasopressin
How does ADH reduce the plasma osmolality
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)
The causes of hyponatraemia can be split into 3 categories: Hypovolaemic hyponatraemia, Euvolaemic hyponatraemia, hypervolaemic hyponataemia.
Define Hypovolaemic hyponatraemia
Reduction in extracellular fluid state with a greater loss of sodium relative to total body water
The causes of hyponatraemia can be split into 3 categories: Hypovolaemic hyponatraemia, Euvolaemic hyponatraemia, hypervolaemic hyponataemia.
Define Euvolaemic hyponatraemia
Hyponatraemia with normal extracellular fluid status
The causes of hyponatraemia can be split into 3 categories: Hypovolaemic hyponatraemia, Euvolaemic hyponatraemia, hypervolaemic hyponataemia.
Define Hypervolaemic hyponataemia
Increase in extracellular fluid status with an increase in total body water relative to sodium
Give examples of causes that causes hyponatraemia secondary to hypovolaemic hyponatraemia
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
Give examples of causes that causes hyponatraemia secondary to euvolaemic hyponatraemia
Hyponatraemia with normal extracellular fluid status
Syndrome of inappropriate ADH release (SIADH) – most common cause
Hypothyroidism
What is the most common cause of hyponatraemia
SIADH
Give examples of causes that causes hyponatraemia secondary to hypervolaemic hyponatraemia
increase in extracellular fluid status with an increase in total body water relative to sodium
- Renal failure
- Heart failure
- Liver failure
- Nephrotic syndrome
What kind of symptoms do the majority of patients with hyponatraemia have
Majority are asymptomatic
The majority of hyponatraemia cases are asymptomatic.
If there are symptoms, give examples of them
- Headache
- Confusion
- Nausea and vomiting
- Lethargy
- Irritability
- Seizures
- Loss of consciousness
- Coma
Neurological symptoms are suggestive of what level of hyponatraemia
Severe hyponatraemia
Name some signs of hypovolaemia
Dry mucous membranes
Capillary refill time > 2 seconds
Dizziness
Thirst
Postural drop in systolic blood pressure
Tachycardia
Name some signs of hypervolaemia
Raised JVP
Bibasal crackles
Gallop rhythm
Peripheral oedema
Hypertensive
How is hyponatraemia diagnosed
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
How is hyponatraemia managed
Depends on the cause – majority is treat the underlying pathology
In general, how is hypovolaemic hyponatraemia managed
IV normal saline
In general, how is hypervolaemic hyponatraemia managed
Fluid restrict + diuretics
What are two potential complications of hyponatraemia
Osmotic demyelination syndrome – if corrected too fast
Cerebral oedema
