Hyponatraemia Flashcards
Definition of hyponatraemia
serum sodium < 135 mmol/l
Biochemical Severe: serum sodium < 125 mmol/l
Normal serum sodium:
135-144mmol
What are the moderate symptoms of hyponatraemia?
Most patients have very few signs and symptoms initially
Headache
Irritability
Nausea / vomiting
Mental slowing
Unstable gait / falls
Confusion / delirium
Disorientation
What are the more severe symptoms of hyponatraemia (acute or chronic)?
Stupor / coma
Convulsions
Respiratory arrest
What happens to the brain in hyponatraemia?
Normal brain (immediate effect of hypotonic state)> Water gain (low osmolality) brain gains water gets bigger causes headaches and causes symptoms (Rapid adaptation) > loss of Na, K, Cl (low osmolality) (Slow adaptation) > Loss of organic osmolytes (low osmolality)
What are the biochemical classifications of Hyponatraemia?
Mild 130-135mmol/l
Moderate 125-129mmol/l
Severe <125mmol/l
What is aetiology of Hyponatraemia?
Hypovolaemic
Euvolaemic
Hypervolaemic
What is the acuity of onset for hyponatraemia?
Acute < 48 hours
Chronic > 48 hours
What is the general treatment for hyponatraemia?
Stop hypotonic fluids
Review drug card/ chart – long list - PPI etc.
What are the specific tests you need to do for hyponatraemia?
Plasma and Urine Osmolality
Urinary Na+
glucose
TFT’s
+/- Assessment of Cortisol
Assessment of underlying causes eg chest imaging
What can happen with fluid overloaded hyponatraemia and how can we treat it?
Cirrhosis of liver/liver failure
Congestive Cardiac failure
Fluid Restrict 500 - 1000ml / 24hrs
What can happen with normovolaemic hyponatraemia and how do we treat it?
Fluid Restrict 500 - 1000ml / 24hrs
What happens if you have low urine Na?
Vomiting and diarrhoea
Burns
Pancreatitis
Sodium depletion after diuretics
What happens if you have urine Na >40mmol/L?
Diuretics
Addison’s (or occasionally pituitary failure)
Cerebral salt wasting
Salt wasting nephropathy
What treatment do you have for low urine Na or Urine Na >40mmol/L?
Saline replacement
What is SIAD?
syndrome of antidiuresis
Features of SIAD?
Too much AVP, when it should not be being secreted
Low osmolality
Plasma sodium is low
Urine is inappropriately concentrated
Water retention - ECF volume increased mildly
Increase GRF - less Na reabsorption in PCT
thus - urine Na+ usually >30mmol/l
normal thyroid and adrenal function
Causes of SIAD:
CNS disorders: Meningitis, Brain tumour, encephalitis etc
Tumours: Carcinomas, lymphomas, leukaemia etc
Respiratory causes: Pneuomonia, Tuberculosis, Severe asthmas
Drugs: Thiazides, PPI’s, oxytocin etc
What are the treatment goals of SIAD?
ensure correct diagnosis
facilitate increase in serum Na+
treat any underlying condition
identify and stop any causative drug (if possible)
in acute setting - daily U+E - hospital
in chronic setting - weekly to monthly U+E - hospital/GP
frequent co-morbidity
Na+>130 mmol/l - usually no need for urgent intervention
What is the management of SIAD?
Diagnose and treat underlying condition
fluid restriction <1L/24 hour
sometimes demeclocycline/ vaptan – acts on collecting duct
if Na+ <115 mmol/l AND fitting hypertonic N/Saline on ITU
<8mmol/l increase in Na+ per 24 hour if chronic
Potential risk of central pontine myelinolysis
Brain and hyponatremia: Treatment after loss of organic osmolytes
Improper therapy: Rapid correction of the hypotonic state - Leads to osmotic demyelination
Proper therapy: Slow correction of the hypotonic state - Normal brain normal osmolality
What is osmotic demyelination syndrome?
White areas in the middle of the pons
Massive demyelination of descending axons
May take up to 2 weeks to manifest
What are the risk factors for Osmotic Demyelination Syndrome (ODS)?
Serum Na+ <105mmol/L
Hypokalaemia
Chronic excess alcohol
Malnutrition
Advanced Liver disease
>18mmol/L Na+ increase in 48 hour
