Hyponatraemia Flashcards
Define Hyponatraemia
Serum Na+ level
< 135mmol/L
3 types of hyponatraemia
- Hypovolaemic (Dehydrated)
- Euvolaemic
- Hypervolaemic (Oedematous)
Hypovolaemic causes of hyponatraemia
Diarrhoea
Vomiting
Medications (e.g. thiazide diuretics)
Adrenal insufficiency
Hyperhidrosis (excess sweating)
3rd space losses (e.g. sepsis, pancreatitis, bowel obstruction)
Define euvolaemic (dilutional) hyponatraemia
No loss of sodium but total body water increases causing a dilutional effect
Euvolaemic hyponatraemia causes
Syndrome of Inappropriate ADH release (SIADH)
Primary polydipsia - water intoxication
Hypothyroidism
Secondary adrenal insufficiency
Exercise-induced hyponatraemia
Hypotonic intravenous fluids
Define Hypervolaemic (Oedematous) hyponatraemia
Both total body water and sodium increase, with a greater increase in water resulting in oedema
Hypervolaemic (oedematous) causes of hyponatraemia
Heart failure
Chronic liver disease
Renal disease (nephrotic syndrome, chronic kidney disease or acute kidney injury)
low albumin –> oedema –> low CO –> more ADH –> more reabsorp H2O
Osmolality formula
2Na + glucose + urea
why is osmolality important
controls distribution of fluid in the body
Define osmosis
when H2O is moving from low osmolality to high osmolality
Define Hypovolaemia (loss of Na+) hyponatraemia
Loss of water and Na+ from the body - more Na+ than water
Hyponatraemia Sx
Lethargy
Anorexia
Headache
Nausea and vomiting
Muscle cramps
Drowsiness
Confusion
Seizures
Hyponatraemia Ix
- Serum osmolality
- Fluid status
- Urine osmolality / Urine sodium
- BT - UEs, TFTs (hypothyroid), 9am cortisol (adrenal insuff.), NT-proBNP (HF), LFTs (ascites; cirrhosis)
what does a high urine osmolality in hypovolaemic hyponatraemia indicates
Renal causes (diurectics / adrenal insuff.) of hyponatraemia
what does a low urine osmolality in hypovolaemic hyponatraemia indicates
Dehydration causes sweating, diarrhoea, vomiting, burns
what does a high urine osmolality in euvolaemic hyponatraemia indicates
Renal reabsorption causes - SIADH
what does a low urine osmolality in hypovolaemic hyponatraemia indicates
Consumption causes - primary polydipsia (H2O intoxication)
Define Pseudohyponatraemia
A falsely low serum sodium level due to an increase in serum lipid or protein content
hyperlipidaemia, cholesterolaemia, glycaemia
Pseudohyponatraemia serum osmolality level
Normal serum osmolality
low for true hyponatraemia
what condition does a low Na+ and high serum osmolality indicate
Hypermolar Hyperglycaemic state (HHS)
2Na + glucose + urea (glucose >40)
Na+ correction max. rate
No faster than 8-10 mmol/L per 24 hours
1st line Mx in SIADH (euvolaemic) / hypervolaemic hyponatraemia
Fluid restriction
Hyponatraemia conservative Mx
- Identifying underlying cause
- Stopping offensive meds (diurectics)
- Fluid restriction
Severe hyponatraemia Mx
Hypertonic (3 - 5%) saline
Hypovolaemia hyponatraemia Mx
IV normal saline
hypovolaemic + urine osmolality >100 mOsm/kg + urine sodium < 30 indications
Consider
- vomiting
- diarrhoea
- burns
- heat exposure (sweating)
- third spacing
Oedema
hypervolaemic + urine osmolality >100 mOsm/kg + urine sodium < 30 indications
Consider
- HF
- liver cirrhosis
- nephrotic syndrome.
hypovolaemic + urine osmolality >100 mOsm/kg + urine sodium >30 in the absence of diuretics or kidney disease indications
Consider
vomiting, primary adrenal insufficiency (Addison’s disease), renal-salt wasting, cerebral salt wasting, or non-prescribed diuretics.
urine osmolality >100 mOsm/kg + urine sodium >30 in the presence of diuretics or kidney disease indications
Consider
- Renal causes
- diurectics
