Hyponatraemia Flashcards
How common is hyponatraemia in hospitals?
30% of in-patients.
Early symptoms of hyponatraemia.
Headache
Nausea
Vomiting
General malaise
Late signs of hyponatraemia.
Confusion
Agitation
Drowsiness
Complications of acute severe hyponatraemia.
Seizures
Respiratory depression
Death
Treatment of acute severe hyponatraemia.
Usually IV saline
Important history of hyponatraemia.
Full history and examination requried.
Drug history and hydration status are of particular importance.
Why is drug history important in hyponatraemia?
Thiazide diuretics can commonly cause hyponatraemia.
Give examples of biochemical investigations done in hyponatraemia.
Serum osmolality
Urine osmolality
Urine sodium
Thyroid function
Assessment of cortisol reserve (0900 cortisol or synacthen test)
What should be given in acute severe hyponatraemia with neurological compromise, regardless of cause?
Hypertonic saline.
This is however a senior decision and should only be done under close supervision.
Complication of untreated acute severe hyponatraemia with neurological compromise.
Cerebral oedema
What should be followed in mild or moderate hyponatraemia?
Diagnostic algorithm.
Explain the diagnostic algorithm.
First off you confirm low serum osmolality.
Once this is confirmed the urine osmolality is checked.
Urine osmolality puts the next step into categories of < 100 mosmol/Kkg or > 100 mosmol/kg.
If > 100 mosmol/kg you need to check urine sodium
Why is it important to confirm low serum osmolality?
To exclude non-hypo-osmolar hyponatraemia
Give an examples of a non-hypo-osmolar hyponatraemia.
Hyperglycaemia
What does a urine osmolality of <100 mosmol/kg suggest?
Primary polydipsia
Inappropriate administration of IV fluid
Low solute intake
What does a urine sodium < 30 mmol/l suggest?
A low effective arterial volume.
When is urine sodium < 30 mmol/l with a low effective arterial volume and hyponatraemia seen?
True dehydration where there is GI salt loss.
When patients are clinically overloaded but have intra-vascular depletion such as congestive heart failure, cirrhosis or nephrotic syndrome.
What should be considered if urine sodium is > 30 mmol/l and the patient is euvolaemic?
SIADH
AVP-like drugs
NSIAD
What is NSIAD?
Nephrogenic syndrome of inappropriate antidiuresis
What must be excluded before confirming SIADH?
ACTH deficiency
What diagnosis is suggested if urine sodium is >30 mmol/l and the patient is dehydrated (low effective arterial volume)?
Addisons
Renal and cerebral salt-wasting
History of vomiting
Why might vomiting cause hyponatraemia with urine sodium >30 mmol/l and dehydration?
Loss of hydrogen ions leading to metabolic alkalosis.
This is then corrected by renal excretion of sodium bicarbonate.
What else might cause hyponatraemia?
Severe hypothyroidism
Mechanism is unclear.
What is SIADH characterised by? (hallmarks)
Low serum osmolality (<275 mosmol/kg)
Urine osmolality > 100 mosmol/kg
Urine sodium > 30 mmol/l
What needs to be excluded before confirming SIADH?
Hypothyroidism
Total salt depletion
ACTH deficiency
ACTH deficiency can look identical to SIADH.
Why?
Because it causes reduced excretion of free water.
This is because cortisol deficiency leads to increased vasopressin activity.
This is not to be confused with hyponatraemia caused by mineralcorticoid deficiency in Addisons disease.
Causes of SIADH.
Malignancy
Respiratory and CNS pathology
Drugs
What malignancy most commonly causes SIADH?
Lung cancer
Drugs that can cause SIADH
Anticonvulsants
If no cause for SIADH is found, what should be done?
Cross-sectional maging or bowel investigation to search for an underlying malignancy.
Idiopathic SIADH is a diagnosis of exclusion.
Management of hypovolaemic hyponatraemia.
Normal saline
Management of hypervolaemic hyponatraemia.
Specialist treatment of cirrhosis, nephrotic syndrome or CCF is indicated.
Management of SIADH.
Fluid restriction (1-1.5 litres a day)
Why is the management of SIADH difficult?
Compliance to drink low amounts of water when you are thirsty is poorly tolerated.
What can be given in SIADH instead?
Demeclocycline
ADH antagonists such as tolvaptan
Treatment of asymptomatic chronic hyponatraemia.
Fluid restriction is often sufficient if they are asymptomatic.
Demeclocycline (ADH antagonist) can be used if required.
If hypervolaemic as well such as in cirrhosis or CCF the underlying disorder should be treated.
Treatment of acute or symptomatic hyponatraemia or if dehydrated.
Cautious rehydration with 0.9% saline but do not correct too quickly because of central pontine myelinolysis.
Maximum rise in serum Na+ should be 15mmol/L per day if chronic, or 1 mmol/L per hour if acute.
Consider using furosemide as well if not hypovolaemic in order to avoid fluid overload.
Be aware of heart failure as well.
When might tolvaptan be used?
It promote water excretion without the loss of electrolytes.
It can be effective in treating hypervolaemic and euvolaemic hyponatraemia but they are expensive
Treatment of emergency hyponatraemia.
Seek expert help.
COnsider hypertonic saline like 1.8% saline at 70 mmol Na+/h and add furosemide as well.
Aim for a gradual increase in plasma Na+ to around 125 mmol/l.
You need to beware of heart failure and central pontine myelinolysis.
