Hyponatraemia

Question 1

What is the most important physiological role of sodium?

Answer 1

Maintaining the volume of the ECF compartment (ECF>volume>circulation)

Question 2

What should you do when you have confirmed hyponataemia?

Answer 2

• Exclude pseudohyponatraemia

* Measure serum osmolality

Question 3

If serum osmolality is normal or high then what should you exclude?

Answer 3

• Hyperglycaemia
• Hypertonic infusion
• Hyperlipidaemia
• Hyperproteinaemia

Question 4

If serum osmolality is low, what should you do?

Answer 4

• Assess the volume status
• Ask to check BP, JVP, oedema
• Look for ascites

Question 5

What are the causes of a hypervolaemic hyponatraemia?

Answer 5

• cirrhosis
• Congestive heart failure
• Nephrotic syndrome

Question 6

What are the causes of hypovolaemic hyponatraemia?

Answer 6

•Extrarenal causes 
 - vomiting 
 - diarrhoea 
 - fluid shift 
•Renal causes 
 - diuretics 
 - salt wasting 
 - nephropathy 
 - adrenal insufficiency

Question 7

How do you exclude pseudohyponatraemia?

Answer 7

• Measure serum osmolality
• Compare to calculated osmolarity: [2 x Na] + Urea + glucose
• If measured = calculated then true hyponatraemia

Question 8

How do you measure corrected Na in the context of extracellular hypertonicity?

Answer 8

[Glucose/4] + measured Na

Question 9

What is the treatment of extracellular hypertonicity?

Answer 9

bring the glucose level down and Na will correct itself

Question 10

What is extacellular hypertonicity?

Answer 10

More water is being drawn into theintravascular space due to the osmotic effect of hyperglycaemia

Question 11

How do you assess the volume status of a patient?

Answer 11

Assess: 
•Volume 
•BP 
•Urine output/fluid status 
•JVP 
•Ascites 
• Oedema

Question 12

What causes a hypovolaemic hyponatraemia (not specific cause)

Answer 12

Na+ depletion

Question 13

What causes a euvolaemic hyponatraemia? (not specific)

Answer 13

• H2O excess
• Excessive intake
• Impaired excretion

Question 14

What are the causes of a hypervolaemic hyponatraemia (not specific)

Answer 14

• Na+ excesss
• H2O excess
• Hypotonic

Question 15

What are the further investigations once you have established someone has a true hypovolaemia?

Answer 15

• Check the urine
• Urine sodium (are they losing or retaining?)
• Urine osmolality (is the urine concentrated or not?)

Question 16

What should you do if you suspect SIADH?

Answer 16

•TFTs to rule out hypothyroidism 
•Short synacthen test to rule out adrenal insufficiency
•Need to ensure: 
  - normal renal function 
  - normal thyroid function 
  - normal adrenal function 
  - not on diuretics

Question 17

What is the aetiology of SIADH?

Answer 17

• Excessive ADH release

* Intracellular and extracellular compartments become expanded but there is no oedema

Question 18

What are the causes of SIADH?

Answer 18

•Pulmonary infections and lesions
•Carcinoma 
•CNS disorders
•AIDS 
•Post op pain or stress
•Vomiting
•Drugs 
- amitriptyline and other tricyclic antidepressants 
- fluoxetine

Question 19

What is the treatment if hypovolaemic?

Answer 19

Isotonic saline

Question 20

What is the treatment if hypervolaemic?

Answer 20

• Salt and fluid restriction
• Loop diuretics
• Advice of a senior

Question 21

What is the treatment if euvolaemic

Answer 21

• Free water restriction

* try 1l/24 hours, may need to go to 500ml/24 hours

Question 22

What is the aim of the treatment of hyponatraemia?

Answer 22

• Increase [Na] gradually: <1mmol/l/hr, <12mmol/l/day, or if asymptotic then <0.5mmol/l/hr
• If symptomatic, may use hypertonic saline but this is consultant led
• Achieve >120mmol/l, then conservative management
• Frequent serum measurement every 2-4 hours
• If reduced GCS then move to high dependency or intensive care

Question 23

What is the pharmacological treatment of hyponatraemia?

Answer 23

• Demeclocycline for 3-4 days, it has a vaspopressin antagonism, functional diabetes insipidus
• Aquaretics - AVP receptor antagonist inducing both a H2O and Na diuresis