MRCP revision battle 24.6: Hyponatraemia

Hyponatraemia is low blood sodium.  The effect of this will depend on how low and for how long.

Possible signs and symptoms include:

• confusion
• seizures
• hypertension
• cardiac failrue
• anorexia
• nausea
• muscle weakness
• oedema

(=CASH MON)


My personal way of dealing with hyponatraemia is to begin by asking 2 cynical questions:

1. is it actually just dilutional? - ?hyperglycaemia 
2. is it actually just pseudo? - ?high protein ?high triglycerides

Once I've got negatives to my cynicism, I move on to ask:

1. are they dehydrated or not?

The divisions from this question onwards are summarised in the diagram below:

If the low sodium is chronic, you treat by:

• treating cause
• giving cautious N.saline if dehydrated
• fluid restricting if not dehydrated.

Occasionally demeclocycline might be needed; this is an antibiotic which has the side effect of inducing nephrogenic diabetes inspidus and hence helps treat SIADH.


Now on to neutrophils...