Friday, 1 October 2010

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

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...