Hyponatraemia

Question 1

What are the causes of Hyponatraemia?

Answer 1

Hypovolaemic - Adrenal insufficiency/Addison’s, AKI, Diuretic Use, Loss from elsewhere (e.g. GI/Trauma)
Euvolaemic – SIADH, Drinking too much water
Hypervolaemic – Heart Failure, Nephrotic Syndrome, Liver Failure

Question 2

What will you find in a history taking of Hyponatraemia?

Answer 2

Symptoms: Caused by Cerebral Oedema
Nausea and vomiting
Altered mental status
Seizures and/or brain herniation and death.

Risk Factors:
Underlying organ failure/disease - Heart/Liver/Kidney
Diuretic Use

Specific Questions to ask:
Recent excessive fluid losses - e.g. severe diarrhoea or vomiting which may point to hypovolaemic hyponatraemia.
Excessive fluid intake, as might occur during high-intensity physical exercise or alcoholism which may point to hypervolaemic hyponatraemia
Respiratory symptoms - SIADH is associated with many lung diseases e.g. pneumonia or small cell lung cancer, as well as GI cancer

Question 3

What will you find on examination of a patient with Hyponatraemia?

Answer 3

To assess fluid status to help differentiate between hypovolemic, hypervolemia or euvolemic causes

End of the bed:
Reduced Skin turgidity 
Hands:
Tachycardia
Hypo-tension with Postural Drop 
Increased Capillary refill time 
Cool peripheries
Face:
Dry Mucous Membranes
Sunken Eyes 
Abdomen:
Reduced urine output
Legs:
Cool peripheries

Examination findings of fluid overload 
Neck:
Raised JVP
Chest:
Tachypnoea
Bibasil Crepitation’s
Pulmonary Oedema on CXR
Legs:
Pitting oedema in sacrum/ankles/legs

Question 4

What investigations will you order in Hyponatraemia ?

Answer 4

Bedside:
Urine osmolality/Urinary Sodium:
Hypovolaemic – Raised Urinary Osmolarity/Sodium indicates renal sodium loss (e.g. Diuretics, Renal failure, Addison’s) and reduced Urinary Osmolarity/Sodium indicates non-renal sodium loss (e.g. gastrointestinal losses)
Euvolaemic - Raised Urinary Osmolarity/Sodium indicates SIADH or high fluid intake
Hypervolaemic - Raised Urinary Osmolarity/Sodium indicates renal Na loss (e.g. CKD or diuretic use) and reduced Urinary Osmolarity/Sodium indicates Oedematous causes (heart failure, cirrhosis, or nephrotic syndrome)
Urine Dipstick – TO assess renal impairment looking for any blood, protein etc

Bloods:
U&E - Serum sodium concentration of <135 mmol/L. Can also assess renal function
Serum osmolality – Can be used to assess fluid levels if unable to from clinical examination (Raised Serum Osmolarity = Dehydration) while (Reduced serum osmolarity = Fluid Overload)
TFT’s - Hypothyroidism can cause Hyponatraemia
LFT’s – Liver Failure can be a cause of hyponatraemia
BNP – Heart Failure can be a cause of hyponatraemia
Serum cortisol/ACTH levels or short Synachten test - To exclude adrenal insufficiency
Lipid Profile - Raised serum lipids can cause false positive hyponatraemia
Glucose - To rule out hyperglycaemia-associated hyponatraemia

Imaging:
CT Brain/Chest/Abdo/Pelvis - Looking for cause of SIADH if found to be cause

Question 5

What is the treatment of Hyponatraemia?

Answer 5

Resuscitation:
A-E approach
Get IV Access/Give O2 to maintain sats of 94+-98
Assessment with AMPLE history and brief examination
Get help - Consider ITU referral
Frequent Observations - Constant or 15 minutely

Medical:
Treat/Manage any underlying cause e.g. Heart Failure, Cirrhosis, SIADH
Asymptomatic and Chronic – Fluid Restriction to 1L/day (for first day, then 500 mL less than daily urine volume from then on)
Symptomatic or Acute – Cautious rehydration with normal Saline (Maximum Na increase 15mmol/day in chronic and 1mmol/hour in acute). May require furosemide if patient is not hypovolaemic to stop fluid overload
In either of the above, if patient is not improving and is Hypervolaemic/Euvolaemic consider Vaptans - Cause fluid loss without any change in electrolyte levels, but expensive
Severe (Seizures/Coma)- Refer to ITU for hypertonic (3%) saline infusion

Question 6

What is hyponatraemia?

Answer 6

Normal sodium levels are between 135 and 145. Any value below 135 is hyponatraemic.
During treatment patients with hyponatraemia are art risk of Central Pontine Myelinosis (Rapid changes in osmolarity cause water loss from Pons cells, damaging myelin sheaths) if Na levels are raised too quickly. This can cause Nausea, Vomiting, Confusion, Headaches and seizures