Hyponatraemia

Serum sodium below <130mmol/L occurs in up to 30% of hospital inpatients and many older patients. However, sudden and dramatic falls in sodium to <120mmol/L can be life-threatening and requires evaluation of fluid status to determine emergency management.

General examination  

Thorough general examination is mandatory in the assessment of any acutely unwell patient.

Pulse, blood pressure and postural blood pressure  

Tachycardia, hypotension and a drop in blood pressure on sitting or standing (>30mmHg) are all indicators of hypovolaemia, although none are highly specific.

Skin turgor and mucous membranes

Reduced skin turgor and dry mucous membranes also support a clinical diagnosis of hypovolaemia.

Mouth breathing and oxygen therapy make the membranes more difficult to assess though, so again these should be considered as supportive evidence of, not confirmation of hypovolaemia.

Respiratory status  

Respiratory signs may indicate a cause for SIADH.

Cardiovascular examination  

Elevation of the JVP, peripheral oedema and pulmonary oedema all indicate hypervolaemia.

Weight

Where possible, it is useful to document a baseline weight particularly if fluid overload is suspected.

Full neurological examination    

This is mandatory in a patient with hyponatreamia. Doctors should look for signs of the severity of hyponatraemia e.g. from mild confusion to agitation to fitting, as well as for possible causes e.g. an acute stroke.

In the very unwell or uncooperative patient this can be difficult but GCS and mini mental state assessment must be documented as a bare minimum.