Hypo and hypernatraemia

Question 1

What are categories of causes of hyponatraemia?

Answer 1

Either occurs in setting of hypo, eu, or hypervolaemia

Question 2

What are causes of hyponatraemia with hypovolaemia?

Answer 2

Renal loss of water: diuretics, RTA, osmotic diuresis, mineralocorticoid deficiency

Extra-renal: vomiting, diarrhoea, third spacing e.g. pancreatitis and burns

Question 3

What are causes of hyponatraemia with euvolaemia?

Answer 3

SIADH
Hypothyroidism

Glucocorticoid deficiency

Question 4

What are causes of hyponatraemia with hypervolaemia?

Answer 4

Nephrotic syndrome

Secondary hyperaldosternonism e.g. HD, liver cirrhosis

Question 5

What is SIADH?

Answer 5

Most common cause of hyponatraemia

Excess production of ADH or inappropriate ADH for plasma osmolality, causing hyponatraemia with inappropriate low plasma osmolality

Question 6

What are causes of SIADH

Answer 6

Cancer: lung/lymphoma/leukaemia

Chest disease: pneumonia

CNS disorders: infections, injury

Drugs: opiates, thiazides, anti-convulsants, proton pump inhibitors, anti-depressants

Question 7

What are Sx of hyponatraemia?

Answer 7

Depend if hypo or hypervolaemic

Weight change, orthostatic hypotension, poor skin turgor, irritability, confusion, weakness, decreased GCS, seizures

Question 8

What are risk factors for hyponatraemia?

Answer 8

• Older age
  
  • Hospitalisation
  • SSRI
  • Thiazides
  • MDMA

May also be artefactual when blood is taken from a drip arm.

Question 9

What Ix in hyponatraemia?

Answer 9

Serum osmolality: will be low.

Urine osmolality: high suggests SIADH or medication, low suggests primary polydispia e.g. just drinking more

Urine Na: will confirm hypo or euvolaemia.

To find out cause: TFTs, cortisol/ACTH to exclude adrenal insufficiency, CT to look for causes of SIADH

Question 10

What urine Na findings in hypovolaemic hyponatraemia?

Answer 10

urine sodium concentration >20 mmol/L indicates renal sodium loss (e.g., diuretics), and ≤20 mmol/L indicates non-renal sodium loss (e.g., gastrointestinal losses).

Question 11

What urine Na findings in hypervolaemic hyponatraemia?

Answer 11

urine sodium concentration >20 mmol/L indicates acute kidney injury/chronic kidney disease or diuretic use, and ≤20 mmol/L indicates congestive heart failure, cirrhosis, or nephrotic syndrome.

Question 12

What is Rx for hyponatraemia

Answer 12

Treat the cause

If acute onset (<48 hours) and/or symptomatic
• Hypertonic %3 saline infusion

If chronic or asymptomatic
• Isotonic fluid infusion
• Fluid restriction to 1L per day
• Furosemide or spironolactone if hypervolaemia

2nd line: vasopressin receptor antagonist and stop fluid restriction

Question 13

What are complications of hyponatraemia?

Answer 13

Cerebral oedema

Central pontine myelinolysis

Question 14

What is function of ADH?

Answer 14

Acts on renal collecting duct to insert aquaporins to reabsorb water

Question 15

What are causes of hypernatraemia?

Answer 15

Free water losses e.g. GI, insensible, renal concentrating defect (DI)

Lack of water intake e.g. inability to access or impaired thirst mechanism

Sodium overload e.g. hypertonic fluids, slat, mineralocorticoid excess

Question 16

What Ix in hypernatraemia?

Answer 16

Serum electrolytes
glucose
Serum osmolality (always high)

Urine osmolality: low = DI, 200-500 = renal concentrating deficit, high = pure volume depletion

• Desmopressin challenge test
• Serum AVP (vasopressin) level
	○ Both for DI MRI or CT brain (DI)

Question 17

What is Rx for hypernatraemia?

Answer 17

• Treat underlying cause
• Give water orally if possible
• If not, give dextrose 5% IV slowly
0.9% saline if hypovolaemic

Question 18

How is diabetes insipidus treated?

Answer 18

Central: desmopressin

Nephrogenic: thiazide

Question 19

What are Sx of hypernatraemia?

Answer 19

• Impaired thirst
	• Diarrhoea and vomiting
	• Oliguria
	• Orthostatic hypotension
	• Decreased JVP
Signs of hypovolaemia: tachycardia, dry mucous membranes

Question 20

What are risk factors for hypervolaemia?

Answer 20

diabetes insipidus
hospital stay
care home resident

Question 21

What are causes of central diabetes insipidus?

Answer 21

Head injury
pituitary surgery
craniopharyngioma

Question 22

What are causes of nephrogenic DI?

Answer 22

genetic e.g. ADH receptor mutation
drugs e.g. lithium
tubulo-interstitial disease

Question 23

What Ix findings suggest DI?

Answer 23

high plasma osmolality, low urine osmolality
water deprivation test still results in dilute urine being made. once desmopressin is given, in nephrogenic DI urine osmolality will stay dilute and in central it will increase