As already mentioned, the commonest setting for the development of acute hyponatraemia is in the post-operative period. The cause is administration of EFW as:
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5% Dextrose or hypotonic saline
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Sips of water
- The generation of EFW by desalination of isotonic saline solutions. If excessive amounts of fluids are given in the face of ADH release, then hypertonic urine is produced leaving EFW.
The problem is often that too much fluid is given rather than the wrong type of fluid. Any patient on i.v. fluids should have their serum electrolytes checked at least daily.
To avoid hyponatraemia:
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Give fluids which are isotonic to the urine if polyuria present and isotonic to the body fluids if the patient is oliguric. Hypotonic intravenous solutions have now been removed from wards because of concerns regarding hyponatraemia.
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Give fluids only to balance ongoing losses and maintain haemodynamic stability. If input = output the levels will remain the same.
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If urine output good, be mindful of conditions which may lead to ADH release:
- ECF volume depletion
- Blood loss
- Hypoalbuminaemia
- Low cardiac output
- Excessive pain, nausea, vomiting or anxiety
- CNS or lung lesions
- Neoplasms or granulomas
- Drugs that enhance the actions of ADH on the kidney by increasing cAMP activity
The most common cause of hyponatraemia in young children is loss of sodium in conditions such as acute gastroenteritis. Loss of fluid leads to a decrease in ECF volume and production of ADH. Commonly hypo-osmolar fluids are given orally and this leads to retention of EFW.
Treatment of the hyponatraemia depends on rapid reexpansion of the ECF volume and a more gradual restoration of ICF volume.
Treatment