Hyponatraemia: assessment and management

Published on 02/03/2015 by admin

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Last modified 02/03/2015

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Hyponatraemia

assessment and management

Severity

In assessing the risk of serious morbidity or mortality in the patient with hyponatraemia, several pieces of information should be used:

The serum sodium concentration itself gives some indication of dangerous or life-threatening hyponatraemia. Many experienced clinicians use a concentration of 120 mmol/L as a threshold in trying to assess risk (the risk declines at concentrations significantly greater than 120 mmol/L, and rises steeply at concentrations less than 120 mmol/L). However, this arbitrary cut-off should be applied with caution, particularly if it is not known how quickly the sodium concentration has fallen from normal to its current level. A patient whose serum sodium falls from 145 to 125 mmol/L in 24 hours may be at great risk.

Often, the clinician must rely exclusively on history and, especially, clinical examination to assess the risk to the patient. Symptoms due to hyponatraemia reflect neurological dysfunction resulting from cerebral overhydration induced by hypo-osmolality. They are non-specific and include nausea, malaise, headache, lethargy and a reduced level of consciousness. Seizures, coma and focal neurological signs are not usually seen until the sodium concentration is less than about 115 mmol/L.

If there is clinical evidence of sodium depletion (see below), there is a high risk of mortality if treatment is not instituted quickly.

Mechanism

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