Hyper/hyponatraemia Flashcards
What is the definition of hypernatraemia?
serum sodium concentration >145 mmol/L
What are 6 clinical features of hypernatraemia?
- Lethargy
- Weakness
- Confusion
- Agitation
- Seizures
- Coma
What are 3 groups of causes of hypernatraemia?
- Excess water loss
- Excessive hypertonic fluid
- Decreased thirst
What are 7 causes of excess water loss that can lead to hypernatraemia?
- Diabetes insipidus
- Diretics
- Osmtic diuresis (E.g. DKA and HHS)
- Diarrhoea
- Vomiting and NG suction
- Sweating
- Burns
What are 3 causes of excessive hypertonic fluid that can lead to hypernatraemia?
- IV infusions
- Total parental nutrition
- Enteral feeds
What are 2 causes of excessive decreased thirst that can lead to hypernatraemia?
- acute illness
- old age
What is the most common cause of hypernatraemia in the elderly?
dehydration - either due to decreased intake or increased GI loss (nausea or vomiting)
What are the 4 commonest causes of hypernatraemia?
- Dehydration
- Osmotic diuresis - HHS, DKA
- Diabetic insipidus
- Excess IV saline
Why must hypernatraemia be corrected with great caution?
although brain tissue can lose sodium and potassium rapidly, lowering of other osmolytes, and importantly water, occurs at a slower rate, predispoing to cerebral oedema, resulting in seizures, coma and death
What is the generally accepted rate of correction of sodium in hypernatraemia?
no greater than 0.5 mmol/hour
What does correction of hypernatraemia involve?
fluids - oral or IV (if IV be careful of overcorrection and cerebral oedema)
What is the definition of hyponatraemia?
serum sodium concentration <135 mmol/L
What are 2 ways that hyponatraemia can be categorised?
- Based on urinary sodium: > or < 20mmol/L
- Based on fluid status: hypovolaemic, euvolaemic or hypervolaemic hyponatraemia
What are 2 causes of pseudohyponatraemia?
- Hyperlipidaemia (increase in serum volume)
- Taking blood from a drip arm
Whatare 5 examples of causes of hyponatraemia when urinary sodium is >20 mmol/L?
- Diuretics: thiazides, loop diuretics
- Addison’s disease
- Diuretic stage of renal failure
- SIADH (urine osmolality > 500 mmol/kg)
- Hypothyroidism
What are 6 causes of hyponatraemia when urinary sodium is <20 mmol/L?
- diarrhoea, vomiting, swaetig
- burns, adenoma of rectum
- secondary hyperaldosteronism: heart failure, liver cirrhosis
- nephrotic syndrome
- IV dextrose
- psychogenic polydipsia
What are 6 causes of hypovolaemic hyponatraemia?
- Burns
- Sweating
- Diarrhoea
- Vomiting
- Fistulae
- Addison’s disease
What are 2 causes of euvolaemic hyponatraemia?
- Syndrome of Inappropriate ADH release (SIADH)
- Hypothyroidism
What are 4 hypervolaemic hyponatraemia?
- Renal failure
- Heart failure
- Liver failure
- Nephrotic syndrome
What determines which tests are performed in hyponatraemia?
if clear cause of hyponatraemia may not be necessary; when cause is not well-defined a number of tests required to confirm/exclude SIADH
What are 5 investigations to perform in hyponatraemia?
- U+Es to confirm
- Urine and plasma paired osmolalities
- Urine sodium
- Urine dip
- TSH and cortisol
Why is it important to measure urea and electrolytes and what condition should be met, when investigating hyponatraemia?
- to confirm hyponatraemia and exclude mixed electrolyte abnormalities which are not seen in SIADH
- patient should not be on diuretics
Why should urine and plasma paired osmolalities be measured in hyponatraemia?
to demonstrate the inappropriate concentration of the urine - occurs in SIADH
Why should urine sodium be measured in hyponatraemia and under what condition?
- to demonstrate sodium wasting in the kidneys
- while not on diuretics
Why should a urine dip be performed in hyponatraemia?
to screen for infection and glomerular pathology
Why should TSH and cortisol be measured in hyponatraemia?
to exclude hypothyroidism (rare caus eof euvolaemia hyponatraemia) and Addison’s disease
What type of hyponatraemia can be caused by hypothyroidism?
euvolaemic hyponatraemia
What are 4 parameters that must be considered when deciding how to treat hyponatraemia?
- Duration of hyponatraemia: acute or chronic
- Severity of hyponatraemia: what is the sodium level
- Symptoms: is the patient symptomatic
- hypovolaemia, euvolaemia, hypervolaemia
What is the difference in duration between acute and chronic hyponatraemia?
acute hyponatraemia is < 48h, chronic is >48h
What usually causes acute hyponatraemia?
excessive fluid intake, parenteral or oral e.g. post-op parenteral fluids and athletes
What is the difference in severity of acute vs chronic hyponatraemia?
acute more likely to be severe
What is the serum Na+ for mild vs moderate vs severe hyponatraemia?
- mild: 130-134 mmol/L
- moderate: 120-129 mmol/L
- severe: <120 mmolL
What are the symptoms of mild, moderate and severe hyponatraemia?
- mild: non-specific symptoms such as headache, lethargy, nausea, vomiting, dizziness, confusion and muscle cramps
- moderate: same as mild
- severe: seizures, coma and respiratory arrest
What is the management of mild hyponatraemia? 2 aspects
- fluid restriction: <800 ml/day
- loop diuretics (furosemide/ bumetanide)
What is the management of moderate hyponatraemia? 3 aspects
- Hypertonic saline in first 3-4 hours to increase sodium >120 mmol/L
- Fluid restriction <800 ml/day
- Loop diuretics
What are 2 aspects of management of severe hyponatraemia?
- bolus of hypertonic saline until symptom resolution
- with or without conivaptan (vasporessin/ADH receptor antagonist)
What are 4 patients in whom fluid intake should be less than urine output in the following patients?
- Oedematous states like heart failure and cirrhosis
- SIADH
- Renal failure
- Psychogenic polydipsia
What is the mechanism of action of conivaptan?
- vasopressin/ ADH receptor antagonist
- acts on V1 and V2 receptors
- V1 receptors cause vasoconstriction while V2 receptors reult in selective water diuresis, sparing the electrolytes
In which patients should vasopressin antagonists such as conivaptan be avoided? 2 key groups
- patients with hypovolaemia hyponatraemia (burns, sweating, diarrhoea, vomiting etc.)
- can be hepatotoxic in patients with underlying liver disease
What is a key side effect of vasopressin/ADH receptor antagonists such as conivaptan?
can stimulate the thirst receptors leading to the desire to drink free water
What are 3 aspects of the management of SIADH?
- fluid restriction
- ADH receptor antagonists (conivaptan, tolvaptan, deomeclocycline)
- Oral sodium and furosemide
- Hypothyroidism
- Levothyroxine
How does the treatment of hypovolaemic vs hypervolaemic hyponatraemia differ?
fluid restriction if hypervolaemic vs IV normal saline if hypovolaemic
What fluids can be given in patients who are unwell with hyponatraemia e.g. having seizures or comatose?
3% saline (but with great care - central pontine myelinosis)
In what setting should 3% NaCl be given for severe hyponatraemia?
critical care
What is the key risk when correcting hyponatraemia?
central pontine myelinosis due to over-correction of severe hyponatraemia
At what rate should hyponatraemia be corrected to avoid central pontine myelinosis?
raise by 4-6 mmol/L in 24hrs (maximum 12 mmol/L)
When do symptoms of central pontine myelinosis occur?
after 2 days, usually irreversible
What are 7 features of central pontine myelinosis?
- Dysarthria
- Dysphagia
- Paraparesis or quadriparesis
- Seizures
- Confusion
- Coma
- Locked-in syndrome
