Hyponatraemia 

With Associate Professor Darren Roberts discusses hyponatraemia, a common yet confusing topic for junior doctors on the wards

Introduction

Hyponatraemia is generally a disorder of water and not salt. It can be generally broken up into hypovolaemic, euvolaemic and hypovolaemic causes. Its management very much depends on its aetiology and its consequences while often are taken lightly can sometimes be quite severe.

Case 1

You are a junior doctor checking blood results before your registrar arrives. You are startled by one patient, an 85-year-old gentleman with community-acquired pneumonia who has a sodium level of 125 mEq/L.

Case 1 – Part 2

After ordering all of the tests and completing your round you go to review the same patient later on in the day. Usually quite a chatty patient, they now seem fatigued and disinterested in your questions, they do however complain of nausea and a headache. Could this be related to their sodium levels?

This indeed could be and is a worrying sign as it may suggest that there is increasing toxicity to the brain and cerebral oedema. Acute hyponatreamia leads to a volume shift from the hypo-osmolar systemic circulation to the higher sodium concentration in the brain which may lead to headaches, confusion, seizures, coma, even herniation and death.