Hyponatraemia: Difference between revisions
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===Investigations=== | ===Investigations=== | ||
====Dehydration==== | |||
*'''[[U+Es]]''' are useful for sodium (obviously) but also assessing dehydration (urea and creatinine). | |||
====Further diagnosis==== | |||
Firstly determine their hydration status. Then the most important things are: | Firstly determine their hydration status. Then the most important things are: | ||
*Urinary sodium | *Urinary sodium | ||
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In '''normovolaemia''': | In '''normovolaemia''': | ||
*Urine osmolality >100mOsmol/kg - [[SIADH]] | *Urine osmolality >100mOsmol/kg - [[SIADH]] | ||
Otherwise, it must be something else. | Otherwise, it must be something else. See [[#Pathophysiology|pathophysiology]]. | ||
===Management=== | ===Management=== | ||
===Prognosis=== | ===Prognosis=== |
Revision as of 15:19, 21 December 2009
Definition
Serum sodium<135mmol/L (<120mmol/L is severe).
Epidemiology
It is the most common electrolyte abnormality. 4.4% of postoperative patient have it. Almost 100% will have had an operation.
Pathophysiology
Broadly speaking there are four groups that the causes of hyponatraemia fall into.
Hypovolaemic
- Kidney problems - Addison's, renal failure, acute tubular necrosis, chronic pyelonephritis, diuretics and others
- Non-renal - diarrhoea and/or vomiting, burns, pancreatitis, trauma, fistula, small bowel obstruction, endurace sport event, heat exposure
Not hypovolaemic
- Oedmatous - nephrotic syndrome, heart failure, cirrhosis, renal failure
- Normovolaemic - SIADH, water overload, severe hypothyroidism, glucocorticoid deficiency
Clinical Features
- Neuro - headache, decreased level of consciouness, cognitive impairment, personality change seizure, brain stem herniation (fixed unilateral dilated pupil, decorticate or decerebrate postuiring, respiratory arrest)
- GI - nausea, vomiting
- General - lethargy, muscle cramps and weakness
- If hypovolaemia - dry mucous membranes, tachycardia, reduced skin turgor
- If hypervolaemia - crackles, third heart sound, raised JVP, peripheral oedema, ascites
Investigations
Dehydration
- U+Es are useful for sodium (obviously) but also assessing dehydration (urea and creatinine).
Further diagnosis
Firstly determine their hydration status. Then the most important things are:
- Urinary sodium
- Urine osmolaLity
The reason being the help to determine which of the causes is most likely. In hypovolaemia:
- Urinary sodium >20mmol/L - renal cause
- Urinary sodium <20mmol/L - non-renal cause
In normovolaemia:
- Urine osmolality >100mOsmol/kg - SIADH
Otherwise, it must be something else. See pathophysiology.