Hypo and hypernatraemia Flashcards
What are categories of causes of hyponatraemia?
Either occurs in setting of hypo, eu, or hypervolaemia
What are causes of hyponatraemia with hypovolaemia?
Renal loss of water: diuretics, RTA, osmotic diuresis, mineralocorticoid deficiency
Extra-renal: vomiting, diarrhoea, third spacing e.g. pancreatitis and burns
What are causes of hyponatraemia with euvolaemia?
SIADH
Hypothyroidism
Glucocorticoid deficiency
What are causes of hyponatraemia with hypervolaemia?
Nephrotic syndrome
Secondary hyperaldosternonism e.g. HD, liver cirrhosis
What is SIADH?
Most common cause of hyponatraemia
Excess production of ADH or inappropriate ADH for plasma osmolality, causing hyponatraemia with inappropriate low plasma osmolality
What are causes of SIADH
Cancer: lung/lymphoma/leukaemia
Chest disease: pneumonia
CNS disorders: infections, injury
Drugs: opiates, thiazides, anti-convulsants, proton pump inhibitors, anti-depressants
What are Sx of hyponatraemia?
Depend if hypo or hypervolaemic
Weight change, orthostatic hypotension, poor skin turgor, irritability, confusion, weakness, decreased GCS, seizures
What are risk factors for hyponatraemia?
- Older age
- Hospitalisation
- SSRI
- Thiazides
- MDMA
May also be artefactual when blood is taken from a drip arm.
What Ix in hyponatraemia?
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
What urine Na findings in hypovolaemic hyponatraemia?
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).
What urine Na findings in hypervolaemic hyponatraemia?
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.
What is Rx for hyponatraemia
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
What are complications of hyponatraemia?
Cerebral oedema
Central pontine myelinolysis
What is function of ADH?
Acts on renal collecting duct to insert aquaporins to reabsorb water
What are causes of hypernatraemia?
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
What Ix in hypernatraemia?
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)
What is Rx for hypernatraemia?
• Treat underlying cause
• Give water orally if possible
• If not, give dextrose 5% IV slowly
0.9% saline if hypovolaemic
How is diabetes insipidus treated?
Central: desmopressin
Nephrogenic: thiazide
What are Sx of hypernatraemia?
• Impaired thirst • Diarrhoea and vomiting • Oliguria • Orthostatic hypotension • Decreased JVP Signs of hypovolaemia: tachycardia, dry mucous membranes
What are risk factors for hypervolaemia?
diabetes insipidus
hospital stay
care home resident
What are causes of central diabetes insipidus?
Head injury
pituitary surgery
craniopharyngioma
What are causes of nephrogenic DI?
genetic e.g. ADH receptor mutation
drugs e.g. lithium
tubulo-interstitial disease
What Ix findings suggest DI?
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
