Hyponatraemia
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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