Causes and interpretation of electrolyte disturbances

Disturbances in electrolyte concentrations have diverse clinical presentations. They may be asymptomatic and detected incidentally. Measuring serum sodium, potassium, calcium, magnesium and phosphate concentrations is usually warranted in patients who present with:

  • symptoms suggestive of electrolyte abnormalities (eg tetany)
  • circulation, cardiac rhythm, hydration, conscious state, urine output or neuromuscular function disturbances
  • bowel, kidney, respiratory or liver function abnormalities.

Identifying an electrolyte abnormality can give a clear lead to the correct diagnosis. Although severe electrolyte abnormalities require prompt empirical treatment, the cause must be identified and corrected.

Rapid complete correction of a severe abnormality can be dangerous—gradual correction is preferred.

The extracellular concentration of a solute may change rapidly in response to:

  • hydration
  • changes in acid–base status
  • fluid shifts in and out of cells (eg with marked changes in plasma glucose concentration).

The following questions should be considered in the management of any electrolyte abnormality:

  • Does the measured abnormality fit the clinical context?
    • If the abnormality does not fit the clinical context, is it confirmed by analysing a fresh sample? (Do not re-analyse the original sample.)
  • Is the patient hypovolaemic, euvolaemic or hypervolaemic?
  • From the clinical context, is the disturbance likely to be acute or chronic? (Chronic electrolyte disturbance is generally better tolerated than acute change.)
  • Could a drug be causing the abnormality?
  • Is the abnormality likely to be transient (eg anticipated to change in the course of other treatment)?
  • Is there an associated acid–base abnormality?
  • Is organ system failure (eg kidney, lung, liver, heart) likely to be responsible for the abnormality?
  • Does failure of an organ system require a modified approach to treatment or monitoring?
  • What is the best way to monitor the response to treatment?

This discussion is limited to managing electrolyte abnormalities in adults. For significant electrolyte abnormalities in children, seek expert advice.