Hypo and hypernatraemia

Question 1

What is the definition of hypernatremia?

Answer 1

• Plasma [Na+] is >146mmol/L
• There is increased solute: water ratio in body fluids
• Increased serum osmolality

Question 2

What are the causes of hypernatremia?

Answer 2

• More commonly caused due to water volume changing rather than mass of Na+ changing
• Osmotic diuresis (e.g. uncontrolled diabetes)
• Fluid loss without replacement (sweating, burns, vomiting)
• Diabetes insipidus (lots of dilute urine produced)
• Incorrect intravenous fluid replacement
• Primary aldosteronism

Question 3

Where is hyponatraemia most common?

Answer 3

• In hospital patients (affects around 10% of patients in hospital)
• Associated mortality of up to 20%

Question 4

What is the definition of hyponatraemia?

Answer 4

• Serum concentration of Na+ lower than 130/135mmol/L
• Usually due to an increase in wate/error in water balance

Question 5

What are the symptoms of hyponatraemia?

Answer 5

• Correlates to severity and rate of onset
• Neurological: agitation, nausea, focal neurology, coma

Question 6

What are the main causes of hyponatraemia?

Answer 6

• Diuretics (mainly thiazides)
• Water overload or retention
• Increased ADH secretion
• Increased plasma osmolality (mannitol, glucose)

Question 7

What are the main causes of hyponatraemia due to true Na+ loss?

Answer 7

• Diarrhoea and vomiting
• Diuretics/renal failure
• Peritonitis
• Burns/CF

Question 8

What are the causes of hyponatraemia due to changes/imbalance in ADH secretion?

Answer 8

• Heart failure
• Kidney disease
• Liver disease
• Tumours (small cell lung cancer)
• SIADH

Question 9

Which medications can cause hyponatraemia?

Answer 9

• Thiazide diuretics
• Selective serotonin reuptake inhibitors
• Proton pump inhibitors
• ACE inhibitors
• Loop diuretics

Question 10

What is the reference range of serum osmolality?

Answer 10

• Serum osmolality is 275-295 mosm/kg

Question 11

What is calculated osmolarity?

Answer 11

• 2Na + glucose + urea (all in mmol/L)

Question 12

What other signs/symptoms would you see in someone who is fluid depleted?

Answer 12

• Pale
• Clammy
• Sweaty
• JVP
• Mucous membranes
• Skin turgor

Question 13

What other signs/symptoms would you see in someone who is oedematous?

Answer 13

• Oedema of lungs
• Ascites
• Extremities affected
• Cough
• SOB

Question 14

What are the causes of hypovolaemic hyponatraemia?

Answer 14

• Vomiting, diarrhoea, fistulas, pancreatitis
• Excessive sweating
• Ascites, peritonitis, burns
• Cerebral salt-wasting syndrome (traumatic brain injury, aneurysmal subarachnoid haemorrhage, intracranial surgery)
• Must distinguish from SIADH

Question 15

What is the treatment for hyponatraemia?

Answer 15

• Depends on the cause
• Fluid restriction nearly always works
• Want to avoid pontine demyelination (occurs with rapid correction of hyponatraemia)
• Infusion of hypertonic saline and furosemide can be used in symptomatic patients