Hyponatraemia

Question 1

What regulates the amount of sodium in the blood?

Under what level is classed as hyponatraemia?

Answer 1

Fluid balance

<135 mol/L

Question 2

What is the main cause?

Answer 2

Impaired water excretion

Question 3

IT IS COMMON IN HOSPITAL AND PREDICTS A POORER PROGNOSIS!

Answer 3

IT IS COMMON IN HOSPITAL AND PREDICTS A POORER PROGNOSIS!

Question 4

Classification:

Hypotonic (hypoosmotic) - commonest:
- How is this subtyped? - 3

Hypertonic - what causes fluid to be pulled into the extracellular space?

Answer 4

Hypovolaemic
Euvolaemic
Hypervolaemia

Hyperglycaemia
Mannitol

Question 5

Causes of hypotonic hyponatraemia:

For each type of hypotonic hyponatraemia, they can be furhter divided into renal and non-renal causes!

Renal causes:

• Will sodium be high/low in the urine?
• Are sodium urine levels >/<20mmol/L?

Non-renal causes

• Will sodium be high/low in the serum?
• Are sodium urine levels >/<20mmol/L?

Answer 5

High sodium in the urine, therefore, low in serum therefore hypotonic

> 20mmol/L - shows sodium is high in urine which drags water out of the body making sodium in the blood low.

Low sodium in serum therefore low sodium in the urine therefore hypotonic

<20mmol/L

Question 6

Causes of hypotonic hyponatraemia:

Hypovolaemic (Dry) causes:

• What GI pathology could cause extra-renal sodium loss?
• Excess diuretics can cause this. What type of diuretic particularly?
• Kidneys may be losing salt in the urine. What could cause kidney disease?

Answer 6

D&V
Burns 
Pancreatitis 
Peritonitis 
Reduced oral fluid intake 

Thiazide diuretics

Interstitial nephritis
PCKD

Question 7

Causes of hypotonic hyponatraemia:

Euvolaemia causes:

• What does euvolemia mean?
• What Rx for resus could, therefore, cause this?
• Polydipsia could cause this. What drug could cause this?
• SIADH is a renal cause for failure to excrete H2O. What does it stand for?

Answer 7

Normal body fluid levels but there is excess H2O intake or it is greater than what the kidneys can handle if there is a disease

IV fluids - COMMON CAUSE

Ecstasy - MDMA

Syndrome of inappropriate ADH secretion

Question 8

Causes of hypotonic hyponatraemia:

Hypervolaemia (oedematous):
- There is organ failure. What organs are failing

Answer 8

Heart failure
Cirrhosis
Nephrotic syndrome
Renal failure - only renal cause

Question 9

S+S:

What flu-like symptoms will they have?

What are some end stage symptoms? - 3

What are some signs of altered volume?

Answer 9

Headache
N&V
Muscle cramps 
Anorexia 
Tired 
Dizzy 
Disorientated 

Seizures
Coma
Cerebral oedema

Low BP
Peripheral oedema

Question 10

Symptoms with gradual onset:

The levels of sodium fall slowly due to cerebral adaption. What is this?

Answer 10

Neurons release inorganic (Na, Cl, K) and organic osmolytes to preserve osmolality

Question 11

Investigations:

Once low sodium is confirmed, what needs to be done to help determine the cause?

Answer 11

Urine sodium

Labs measure osmolality but the difference between osmolality and osmolarity is not clinically important!

Question 12

Management:

Unless hypovolaemic, what should the patient be instructed to do?

What fluid can be given if they are in shock?

THERE IS FURTHER RX!

Answer 12

Fluid restriction - to prevent diluting ECF and causing a further drop-in hypovolaemia

Hypertonic saline